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373 articles found.
Effect of aft wall slope on cavity pressure oscillations in supersonic flows
01/05/2009
N. S. Vikramaditya and J. Kurian
An experimental study of supersonic flow over wall mounted cavities with different aft wall angles is carried out. Unsteady pressure measurements were made on the walls and floor of the cavity. Data analysis was performed on the experimental results using statistical methods. In the case of higher angled cavities, the presence of an upstream traveling acoustic wave could be confirmed. For lower angled cavities (60 degrees and less) where the acoustic wave could not be identified, the flow inside the cavity was more or less stable. Mode switching occurring in higher angled cavities was confirmed by spectrogram studies.
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A new model for optimal TF/TA flight path design problem
01/05/2009
R. Zardashti and M. Bagherian
This paper focuses on the three dimensional flight path planning for a UAV on a low altitude terrain following/terrain avoidance mission. Using an approximate grid-based discretisation scheme, we transform the continuous optimisation problem into a search problem over a finite network, and apply a variant of the shortest-path algorithm to this problem. In other words using the three dimensional terrain information, three dimensional flight path from a starting point to an end point, minimising a cost function and regarding the kinematics constraints of the UAV is calculated. A network flow model is constructed based on the digital terrain elevation data (DTED) and a layered network is obtained. The cost function for each arc is defined as the length of the arc, then a constrained shortest path algorithm which considers the kinematics and the altitude constraints of the UAV is used to obtain the best route. Moreover the important performance parameters of the UAV are discussed. Finally a new algorithm is proposed to smooth the path in order to reduce the workload of the autopilot and control system of the UAV. The numeric results are presented to verify the capability of the procedure to generate admissible route in minimum possible time in comparison to the previous procedures. So this algorithm is potentially suited for using in online systems.
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Effects of boundary-layers bleeding on unstart/restart characteristics of hypersonic inlets
01/05/2009
J. Chang, D. Yu, W. Bao, Y. Fan and Y. Shen
A series of mixed-compression hypersonic inlets at different bleeding rates were simulated at different freestream conditions in this paper. The unstart/restart characteristics of hypersonic inlets were analysed and the reasons why the unstart/restart phenomenon is in existence is presented. The unstart/restart characteristics of hypersonic inlets at different bleeding rates were given. The effects of boundary-layer bleeding on the performance parameter (mass-captured coefficient, total-pressure recovery coefficient), starting and restarting Mach number of hypersonic inlets were discussed. In conclusion, boundary-layer bleeding can improve the performance parameter of hypersonic inlets, and can reduce the starting and restarting Mach number, and can broad the operation range of the hypersonic inlet.
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Predicting the response of low-aspect ratio, flexible aircraft
01/04/2009
L. Meirovitch, I. Tuzcu and W.D. McGrory
Accurate prediction of the response of low-aspect ratio, flexible aircraft requires correspondingly accurate modeling of the aircraft itself and of the aerodynamic forces, both respectable problems. Assuming that the wing can be modeled as a nonuniform plate, the discretisation process of choice is the finite element method (FEM), which demands a very large number of degrees of freedom for good accuracy. Moreover, accurate modeling of the aerodynamic forces acting on the aircraft suggests the use of computational fluid dynamics (CFD), which requires the use of an extremely large number of variables. On the other hand, feedback control design for the aircraft demands an aircraft model of relatively small order, so that the dimension of the FEM and CFD models must be reduced drastically. Based on physical considerations, reasonably accurate model reductions can be achieved, but a problem remains because the FEM and CFD grids are likely to differ from one another. It is shown in this paper how to achieve desirable model reductions for both the FEM and CFD and how to integrate the aerodynamic forces into the aircraft state equations. A numerical example demonstrates how the theory can be applied to the flight of a flexible aircraft. The analytical/computational approach developed here should permit parametric studies ultimately resulting in a reduction in the time required for aircraft design and flight testing.
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A CFD assessment of classifications for hypersonic inlet start/unstart phenomena
01/04/2009
J. Chang, D. Yu, W. Bao, Z. Xie and Y. Fan
Inlet start/unstart detection is one of the most important issues of hypersonic inlets and is also the foundation of protection controls of scramjets. In ground and flight tests, it is inevitably to introduce the sensor noises to the measurement system. How to overcome or weaken the influence of the sensor noises and the outer disturbances is an important issue to the control system of the engine. To solve this problem, the 2D inner steady flow of hypersonic inlets was numerically simulated in different freestream conditions and backpressures, and two different inlet unstart phenomena were analysed. The membership function for hypersonic inlet start/unstart can be obtained by using probabilistic output support vector machine, and the algorithm of multiple classifiers fusion is introduced. The variations of the classification accuracy with the intensity of the sensor noises and the number of the classifier were discussed respectively. In conclusion, it is useful to introduce the algorithm of support vector machine and multiple classifiers fusion to overcome or weaken the influence of the sensor noises on the classification accuracy of hypersonic inlet start/unstart. The number of the practical fusion classifiers needs a tradeoff between the fusion classification accuracy and the complexity of the classification system.
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Aircraft parameter estimation using a new filtering technique based upon a neural network and Gauss-Newton method
01/04/2009
N. K. Peyada and A. K. Ghosh
A new parameter estimation method based upon neural network is proposed. The method proposed here uses feed forward neural networks to establish a neural model that could be used to predict subsequent time histories given the suitable measured initial conditions. The proposed neural model would not represent a generic flight dynamic model. The neural model in this case develops point to point fitting of the input and the output data. Thus, it could at best be referred to as flight dynamic model in restricted sense. Gauss-Newton method is then used to obtain optimal values of the aerodynamic parameters by minimising a suitable defined error cost function. The method has been validated using longitudinal and lateral-directional flight data of various test aircraft. The results thus obtained were compared with those obtained through wind tunnel test, or those obtained using Maximum likelihood and/or Filter error methods. Unlike, most of the parameter estimation methods, the proposed method does not require a prior description of the model. It also bypasses the requirement of solving equations of motion. This feature of the proposed method may have special significance in handling flight data of an unstable aircraft.
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Downward pointing winglet design and assessment within the M-DAW research project
01/04/2009
J.-L. Hantrais-Gervois, R. Grenon, A. Mann and A. Büscher
The design and performance analysis of a wing tip device proposed within the M-DAW project by ONERA is presented. A proto-design process is described and the device was thoroughly assessed (mainly with Reynolds-Averaged Navier-Stokes simulations). The process was further explained through wind-tunnel tests at both low speed and high speed in the pressurised and cryogenic European transonic wind tunnel in Cologne. The device is a downward pointing winglet designed for a retrofit scenario (the wing could be modified only within the 96% – 100% bounds of the span). It was designed to keep the wing root bending moment of the clean wing at cruise unchanged so that the aerodynamic gains are the net gains provided by the device that can be directly installed without structural modifications of the wing.
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Control of separation in the concave portion of contraction to improve the flow quality
01/03/2009
K. Ghorbanian, M. R. Soltani, M. D. Manshadi and M. Mirzaei
Subsonic wind tunnel experiments were conducted to study the effect of forced transition on the pressure distribution in the concave portion of contraction. Further more, the effect of early transition on the turbulence level in the test section of the wind tunnel is studied. Measurements were performed by installing several trip strips at two different positions in the concave portion of the contraction. The results show that installation of the trip strips, have significant effects on both turbulence intensity and on the pressure distribution. The reduction in the free stream turbulence as well as the wall static pressure distribution varied significantly with the location of the trip strip. The results confirm the significant impact of the tripped boundary layer on the control of adverse pressure gradient. The trip strip at X/L = 0.115 improves pressure distribution in contraction and reduces turbulence intensity in the test section, considerably.
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Numerical and experimental investigation of tip leakage flow and heat transfer using idealised rotor-tip models at transonic conditions
01/03/2009
S.K. Krishnababu, H.P. Hodson, W.N. Dawes, P.J. Newton and G.D. Lock
The effect of tip geometry on discharge coefficient and heat transfer is investigated both experimentally and numerically using idealised models of an unshrouded rotor blade. A flat tip was compared with two squealer-type geometries (a cavity and suction-side squealer) under the transonic conditions expected in the gas turbine engine. Heat transfer measurements were performed using a transient liquid crystal technique while a duplicate test section was used for measuring the pressure field. Computations were carried out using an unstructured, fully compressible, three-dimensional RANS (Reynolds averaged Navier Stokes) solver. Initial computations performed using a low Reynolds number k- model demonstrated the inability of the model to predict the Nusselt number with reasonable accuracy. Further computations performed using a low Reynolds number k- model improved the predictions dramatically. The computed discharge coefficient and the average Nusselt number over the blade tip agreed well with the experiments. Three upstream-total to exit-static pressure ratios were used to create a range of engine-representative Mach numbers. Both experimental and numerical studies at the lower pressure ratio of 1×3 (exit Mach number ~ 0×65) established the cavity geometry as the best performer from an aerodynamic perspective by reducing the discharge through the tip. However, from the heat transfer perspective, both the peak Nusselt number and the average heat transfer to the tip were higher than the flat tip. At the higher pressure ratios of 1×85 and 2×27 (corresponding to exit Mach numbers ~ 0×98 and 1×12) the discharge coefficient and heat transfer to the tip increases. This paper explores the fluid dynamics associated with these flows and shows that the highest heat transfer is caused by reattachment and flow impingement. The fluid dynamic computations provide insight into the experimental measurements and were successfully compared with simple analytical models.
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Identification of a MIMO state space model of an F/A-18 aircraft using a subspace method
01/03/2009
Identification of a MIMO state space model of an F/A-18 aircraft using a subspace method
The aim of this paper is to determine the mathematical relationship (model) between control deflections and structural deflections of the F/A-18 modified aircraft in the active aeroelastic wing technology program. Five sets of signals from flight flutter tests corresponding to the excited sources were measured by NASA Dryden Flight Research Center. These excitation inputs are: differential ailerons, collective ailerons, collective stabilisers, differential stabilisers, and rudders. The signals to be used by the model are of two types: control deflection time histories and corresponding structural deflections on the wing and trailing-edge flaps. We choose to use the subspace identification method based on reconstructing the observability matrix in order to identify the nonlinear multi-input, linear-in-the-states, multi-output system. We identify models (input/output characteristics) by applying this method for a number of sixteen flight conditions for which the Mach number varies from 0·85 to 1·30 and the altitudes vary from 5,000ft to 25,000ft. Very good results are obtained with a fit between the estimated and the measured signals and a correlation coefficient higher than 90%.
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The optimum aeroplane and beyond
01/03/2009
D. I. A. Poll
A summary of the ways in which aviation impacts the environment is presented and the ratio of the energy liberated during a flight to the revenue work done (ETRW) is identified as a key indicator in the assessment of environmental impact. Using the ‘Breguet’ range equation, a number of theorems relating to ETRW are derived and discussed. This is followed by an approximate analysis to produce estimates for the ETRW of aircraft currently in service. It is found that the global fleet average value for ETRW is much higher than those estimated for existing individual aircraft. An explanation of the difference is presented, with the contributions from airline operations and air traffic management identified and quantified. Consideration is then given to the potential for future reduction in ETRW through advances in materials, alternative fuels, structures, aerodynamics and propulsion technologies and the likely benefits are quantified. The improvement in ETRW that could be achieved if this parameter was minimised in the design process with the current level of technology is also considered. Finally, the likelihood of performance improvements being introduced in the short, medium and long term is briefly discussed.
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Numerical simulation of fluid-structure interaction in the opening process of conical parachute
01/03/2009
Y. Cao, Z. Wu, Q. Song and J. Sheridan
According to multi-node model, the dynamics equations of conical parachute system for simulating shape deformation process of the flexible canopy in the opening process were established. With the combination of dynamics equations code and computational fluid dynamics (CFD) software, the fluid-structure interaction investigation of the conical parachute was carried out. Also the change of parachute shape and flow field, inflation time, the rate of descent, the distance of descent, and other relevant data were achieved. This paper has focused on analysing vortex structure of the flow field in the opening process of conical parachute, and laid the foundation for studying mechanics mechanism of flow field variation of conical parachute in future.
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Large Eddy Simulation of a complete Harrier aircraft in ground effect
01/02/2009
G.J. Page and J.J. McGuirk
This paper aims to demonstrate the viability of using the large eddy simulation (LES) CFD methodology to model a representative, complete STOVL aircraft geometry at touch down. The flowfield beneath such a jet-borne vertical landing aircraft is inherently unsteady. Hence, it is argued in the present work that the LES technique is the most suitable tool to predict both the mean flow and unsteady fluctuations, and, with further development and validation testing, this approach could be a replacement, and certainly a complementary aid, to expensive rig programmes. The numerical method uses a compressible solver on a mixed element unstructured mesh. Examination of instantaneous flowfield predictions from these LES calculations indicate close similarity with many flow features identified from ground effect flow visualisations, which are well known to be difficult to model using RANS-based CFD. Whilst significant further work needs to be carried out, these calculations show that LES could be a practical tool to model , for example, Hot Gas Ingestion for the Joint Strike Fighter aircraft.
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On the characteristics of a twin-jet STOVL fountain
01/02/2009
A. J. Saddington, K. Knowles and P. M. Cabrita
The interaction of multiple jets with the ground is of great importance for the design and operation of short take-off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry and laser Doppler velocimetry. Measurements were made with nozzle pressure ratios of between 1.05 and 4, nozzle height-to-diameter ratios of between 2.4 and 8.4, nozzle splay angles of between ±15 degrees and a nozzle spacing-to-diameter ratio of seven. The effect of varying these parameters on the fountain velocity decay, spreading rate and momentum flux ratio are discussed. Mean fountain upwash velocity profiles were found to be self-similar for all test conditions. A distinct frequency of fountain oscillation was identified but only at a nozzle height of 4.4 diameters.
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VSTOL Aircraft market analysis
01/02/2009
D. K. Howarth
This paper describes the market for air vehicles that offer Very Short Take Off and Landing (VSTOL) capabilities, also known as VSTOL aircraft. A commercial VSTOL aircraft will only succeed if it provides profits to both manufacturers and airlines. Being able to operate out of shorter fields offers airlines greater flexibility and therefore provides a benefit to the airline. However, adding VSTOL performance also adds cost. Successful VSTOL aircraft designs must balance the added cost against the additional benefits VSTOL performance will provide.
The first problem in any new VSTOL design is determining what field length provides the maximum benefit relative to cost. In order to be able to determine this one needs to know not only what it will cost to design and build the new aircraft, but its value to the airlines, as reflected by the demand for it and the price they are willing to pay. Only then is it possible to design the aeroplane the market wants at a sustainable price and in sufficient quantities to optimise the manufacturer’s return on investment.
This paper is a comprehensive parametric analysis of helicopters and aeroplanes that shows how much the market values short field performance by determining how much airline customers have been paying for it and how the market reacts to changes in its price. The analysis simultaneously considers over 230 currently produced models of fixed wing and rotary commercial aircraft, ranging in size from a Cessna 172 to an Airbus A380 and with balanced field lengths ranging from less than 150 to over 10,500ft.
The data show that a single, statistically significant demand curve exists for all of these vehicles, with prices that range across several orders of magnitude. This curve consists of several segments or sub-markets including those for regional and rotary wing aircraft. Both of those markets offer vehicles over a wide range of prices. The analysis shows that VSTOL price is a function of the balanced field length provided by the vehicles within these market segments. Comparing demand and sustained price against cost reveals particular field lengths for which it will be possible to make a profit building VSTOL aircraft.
Because the sustained price for a VSTOL aircraft is a function of its field length performance, and the quantity of a model sold is a function of its price, it follows that it is possible to predict the profit potential for a given VSTOL design in advance of its development. A thorough study of potential configurations therefore offers manufacturers the ability to design VSTOL aircraft that provide the maximum possible profit while fully satisfying the requirements of their airline customers.
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The optimum aeroplane and beyond
01/02/2009
D. I. A. Poll
A summary of the ways in which aviation impacts the environment is presented and the ratio of the energy liberated during a flight to the revenue work done (ETRW) is identified as a key indicator in the assessment of environmental impact. Using the ‘Breguet’ range equation, a number of theorems relating to ETRW are derived and discussed. This is followed by an approximate analysis to produce estimates for the ETRW of aircraft currently in service. It is found that the global fleet average value for ETRW is much higher than those estimated for existing individual aircraft. An explanation of the difference is presented, with the contributions from airline operations and air traffic management identified and quantified. Consideration is then given to the potential for future reduction in ETRW through advances in materials, alternative fuels, structures, aerodynamics and propulsion technologies and the likely benefits are quantified. The improvement in ETRW that could be achieved if this parameter was minimised in the design process with the current level of technology is also considered. Finally, the likelihood of performance improvements being introduced in the short, medium and long term is briefly discussed.
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Wind tunnel testing of powered lift, all-wing STOL model
01/02/2009
S.W. Collins, B.W. Westra, J.C. Lin, G.S. Jones and C.H. Zeune
Short take-off and landing (STOL) systems can offer significant capabilities to warfighters and, for civil operators thriving on maximising efficiencies they can improve airspace use while containing noise within airport environments. In order to provide data for next generation systems, a wind tunnel test of an all-wing cruise efficient, short take-off and landing (CE STOL) configuration was conducted in the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) 14ft by 22ft Subsonic Wind Tunnel. The test’s purpose was to mature the aerodynamic aspects of an integrated powered lift system within an advanced mobility configuration capable of CE STOL. The full-span model made use of steady flap blowing and a lifting centerbody to achieve high lift coefficients. The test occurred during April through June of 2007 and included objectives for advancing the state-of-the-art of powered lift testing through gathering force and moment data, on-body pressure data, and off-body flow field measurements during automatically controlled blowing conditions. Data were obtained for variations in model configuration, angles of attack and sideslip, blowing coefficient, and height above ground. The database produced by this effort is being used to advance design techniques and computational tools for developing systems with integrated powered lift technologies.
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Highlights of the Lockheed Martin F-35 STOVL jet effects programme
01/02/2009
R. Hoggarth and R. Mange
This paper presents the highlights of the F-35 STOVL Jet Effects (SJE) test effort during the complete four years of the System Development and Demonstration phase. A new 12%-scale F-35 SJE model was tested in the German-Dutch wind-tunnels Large Low Speed Facility in order to gather STOVL jet-induced Forces and Moments. Ten separate test entries were conducted, covering all STOVL flight regimes from pure hover in ground effect through transition to wing borne flight. This paper will present an overview of this programme, including a detailed description of the wind-tunnel model, testing techniques, test conditions, and accomplishments.
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Development of a VTOL mini UAV for multi-tasking missions
01/02/2009
B. Bataillé, J.-M. Moschetta, D. Poinsot, C. Bérard and A. Piquereau
Recent developments in the field of Mini-UAVs lead to successful designs in both hovering rotorcraft and fixed wing aircraft. However, a polyvalent MAV capable of stable hovering and fast forward flight is still expected. A promising candidate for such versatile missions consists of a tilt-body tail-sitter configuration. That concept is studied in this paper both from the flight mechanics and control points of view. Developments are based on an existing prototype called Vertigo. It consists of a tail sitter fixed-wing mini-UAV equipped with a contra-rotating pair of propellers in tractor configuration.
A wind-tunnel campaign was carried out to extract experimental results from the Vertigo aerodynamic characteristics. A 6-component sting balance was fitted in the powered model enabling excursion in angles of attack and sideslip angles up to 90°. Thus, a detailed understanding of the transition mechanism could be obtained. An analytical model including propwash effects was derived from experimental results.
The analytical model was used to compute stability modes for specific flight conditions. This allowed an appropriate design of the autopilot capable of stabilisation and control over the whole flight envelope. A gain sequencing technique was chosen to ensure stability while minimising control loop execution time. A MATLAB-based flight simulator including an analytical model for the propeller slipstream has been developed in order to test the validity of airborne control loops.
Simulation results are presented in the paper including hover flight, forward flight and transitions. Flight tests lead to successful inbound and outbound transitions of the Vertigo.
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Interactional aerodynamics and acoustics of a hingeless coaxial helicopter with an auxiliary propeller in forward flight
01/02/2009
H.W. Kim, A.R. Kenyon, R.E. Brown and K. Duraisamy
The aerodynamics and acoustics of a generic coaxial helicopter with a stiff main rotor system and a tail-mounted propulsor are investigated using Brown’s Vorticity Transport Model. In particular, the model is used to capture the aerodynamic interactions that arise between the various components of the configuration. By comparing the aerodynamics of the full configuration of the helicopter to the aerodynamics of various combinations of its sub-components, the influence of these aerodynamic interactions on the behaviour of the system can be isolated. Many of the interactions follow a simple relationship between cause and effect. For instance, ingestion of the main rotor wake produces a direct effect on the unsteadiness in the thrust produced by the propulsor. The causal relationship for other interdependencies within the system is found to be more obscure. For instance, a dependence of the acoustic signature of the aircraft on the tailplane design originates in the changes in loading on the main rotor that arise from the requirement to trim the load on the tailplane that is induced by its interaction with the main rotor wake. The traditional approach to the analysis of interactional effects on the performance of the helicopter relies on characterising the system in terms of a network of possible interactions between the separate components of its configuration. This approach, although conceptually appealing, may obscure the closed-loop nature of some of the aerodynamic interactions within the helicopter system. It is suggested that modern numerical simulation techniques may be ready to supplant any overt reliance on this reductionist type approach and hence may help to forestall future repetition of the long history of unforeseen, interaction-induced dynamic problems that have arisen in various new helicopter designs.
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CVF ski-jump ramp profile optimisation for F-35B
01/02/2009
A. Fry, R. Cook and N. Revill
This paper presents a summary of the principles and processes used to design a ski-jump ramp profile for the UK’s Future Aircraft Carrier (CVF) optimised for the Joint Strike Fighter (JSF).
The paper includes an overview of the CVF and JSF programs, a history and summary of the ski-jump ramp and the principles of its use in the shipborne Short Take-Off (STO) manoeuvre.
The paper discusses the importance of defining optimisation boundaries including specified objectives, aircraft configurations and environmental conditions. It then demonstrates the process of balancing the design drivers of air vehicle performance and landing gear loads to achieve an optimum profile. Comparisons are made between the proposed candidate CVF ramp profile and the current in service ski-jump design as designed for the Harrier family of aircraft.
The paper briefly covers some of the important issues and factors that have been experienced when a theoretical profile is translated into a physical ramp fitted to a ship, principally the effects on aircraft operations due to build and in-service variation from the nominal profile.
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Air power and the future battlespace
01/01/2009
C. J. M. Goulter
The aim of this paper is to consider the role of air power in the future, within the wider security environment and across the full spectrum of conflict. The key is to make some reasonable assumptions about the future strategic environment for the next ten to fifteen years, extrapolating from our experience since the end of the cold war and our existing knowledge of potential state threats and sub-state threats and challenges. One of our failings since the end of the cold war has been to focus on the operational level of war at the expense of thinking hard about national strategy. The formulation of national strategy is supposed to be directed by government, but if that government fails to provide strategic direction, as it has done over recent years, the result is short-termist perspectives, and a ‘hand to mouth’ approach to crisis management. This has been reinforced further by financial constraint and the electoral cycle. Ideally, a strategic perspective helps us not only to set our current age in a much wider context, thus preventing or making us less inclined to ‘knee-jerk’ reactions to single events, but it also assists in the making of correct judgements about the nature of a conflict or scenario, thus enabling us to apply the appropriate type of tool (air power or otherwise). History is littered with instances of the inappropriate use of military force, and air power is no exception, and we cannot afford nugatory manpower and material expenditure. The challenge is, therefore, enormous: to meet current commitments, while preparing for future possibilities.
The paper’s principle contention is that we will be committed to counter-insurgency scenarios for the foreseeable future, which, it should be emphasised, represents a continuum of COIN commitment since the end of the Second World War, and that these commitments will consume a major proportion of defence resources(1). Indeed, it is a stated air force planning assumption that it will continue to support land operations in Iraq and Afghanistan, in essence, for as long as it takes(2). However, it is also the paper’s contention that we should not focus on counter-insurgency operations to the exclusion of other possible commitments. This paper is intended, in part, to be a corrective to the dangerous line of argumentation appearing after 9/11 which advocated our completely reconfiguring our armed services to meet the terrorist threat. The danger posed by rogue states has not evaporated, and there is still a requirement for strategic effect operations, or at the very least deterrence, against nations which pose a threat to our national security. The paper also aims to redress the balance after a decade of viewing air power very largely as a supporting component in the joint environment. The paper also seeks to challenge the accepted wisdom that joint means land supported by maritime and air. The nature of a conflict or whatever the scenario determines which Service environment is dominant, and this can change over time. In short, we must be able to operate effectively across the full military spectrum, from peace support operations (PSO), through to counter-insurgency (COIN), to ‘high end’ war-fighting.
Given Britain’s financial constraints, we cannot afford to recapitalise the RAF in the foreseeable future, and so we must think harder about how we utilise what assets we have. This does not mean purely thinking about which platforms can perform what variety of roles, but it entails a fundamental step change in air power conceptualisation in this country and, in particular, invigorating the RAF so that it becomes a far more thoughtful organisation. Good doctrinal and conceptual work is, in itself, a vital force multiplier, especially in financially constrained times. The effects based approach (EBA) will play a major part in this. An emphasis on second and third order effects analysis has already replaced the one-dimensional ‘weapons effect’ focus common during the 20th Century. This new emphasis is particularly important in wars of choice, during which the application of any type of military force is problematic because of the multitude of political constraints, but also because of the politicians’ penchant for using air power as a ‘quick win’, limited footprint option. In the immediate term, additional work urgently needs to be done on counter-insurgency warfare and air power effect, especially non-kinetic effect and the psychological impact of air power. We must also, necessarily, continue to develop our relationship with the Americans, who will provide an essential insurance policy against big state and conventional threats in the future. Concurrently, we must encourage qualitative and quantitative capability development within NATO and the EU. This is vital, both to protect Europe from any potential big state threats, and also to foster greater capability burden sharing across NATO and the EU in current and future expeditionary operations.
This paper will consider a variety of issues: air power for strategic effect and UK current and near-term air power capability. The second half of the paper will address air power in COIN, including its limitations and measuring effect in COIN, and air power innovation in COIN.
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Experimental investigation of the aerodynamic characteristics of generic fan-in-wing configurations
01/01/2009
N. Thouault, C. Breitsamter, N. A. Adams, C. Gologan and J. Seifert
This experimental investigation concentrates on the aerodynamic behaviour of a generic fan-in-wing configuration. The effects of the fan(s) on the flow circulation in a short take-off and landing or a transition flight condition without ground effect are evaluated. A wind-tunnel model has been constructed and tested to quantify the aerodynamic effects. Force measurements, surface pressure measurements, stereo-particle image velocimetry and wool tufts flow visualisation are performed. Different fan-in-wing configurations with the fans rotating in the wing plane, one fan either at the rear or front part of the wing and two fans are compared to the closed wing without fans set as reference. A fan placed near the trailing edge improves significantly the lift coefficient due to a jet flap effect on the wing lower side combined with enhanced suction on the wing upper side. The jet exiting the nozzle rolls up in a counter rotating pair of vortices affecting significantly the wing behaviour.
This experimental investigation constitutes also a useful database for further CFD comparison.
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Trajectory optimisation of an aerobatic air race
01/01/2009
H. van der Plas and H. G. Vasser
This paper deals with the synthesis of optimal trajectories for aerobatic air races. A typical example of an air race event is the Red Bull Air Race World Series, where high-performance aerobatic aircraft fly a prescribed slalom course consisting of specially designed inflatable pylons, known as ‘air gates’, in the fastest possible time. The trajectory that we seek to optimise is based on such a course. The air race problem is formulated as a minimum-time optimal control problem and solved in open-loop form using a direct numerical multi-phase trajectory optimisation approach based on collocation and non-linear programming. The multiphase feature of the employed collocation algorithm is used to enable a Receding-Horizon optimisation approach, in which only a limited number of manoeuvres in sequence is considered. It is shown that the Receding-Horizon control approach provides a near-optimal solution at a significantly reduced computational cost relative to trajectory optimisation over the entire course. To avoid the path inclination singularity in the equations of motion based on Euler angles, a point-mass model formulation is used that is based on quaternions. Numerical results are presented for an Extra 300S, a purpose-designed aerobatic aircraft.
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Contrail avoidance in the aircraft design process
01/12/2008
F. Noppel and R. Singh
As aviation is one of the fastest growing industrial sectors world wide, air-traffic emissions are projected to increase their stake in the contribution to global warming. According to studies, both carbon dioxide and contrails are the principal air-traffic pollutants, whereas the impact from contrails in terms of radiative forcing is possibly larger than that of all other air-traffic pollutants combined. New regulations with the objective of mitigating contrail occurrences might cause a change in the design requirements of aircraft. In light of this, a method considering contrail formation during the aircraft design process is presented in this paper. Aircraft performance and optimisation is carried out with NASA’s flight optimisation system. Combining historical meteorological data with air-traffic data enables an assessment regarding contrail formation. As an example, a particular aircraft type in terms of range, speed and payload is optimised for minimum block fuel consumption considering different altitudes. The change in contrail formation in terms of contrail-km formed is calculated. The results suggest that if aircraft of the considered class were designed for higher altitudes, contrail occurrences would diminish slightly at a non-negligible fuel burn penalty.
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Effect of amplitude and mean angle-of-attack on the boundary layer of an oscillating aerofoil
01/12/2008
M. R. Soltani and A. Bakhshalipour
Extensive experiments were conducted to study the effect of various parameters on the surface pressure distribution and transition point of an aerofoil section used in a wind turbine blade. In this paper details of the variation of transition point on the aforementioned aerofoil are presented. The aerofoil spanned the wind-tunnel test section and was oscillated sinusoidally in pitch about the quarter chord. The imposed variables of the experiments were free stream velocity, amplitude of motion, mean angle-of-attack, and oscillation frequency.
The spatial-temporal progressions of the leading-edge transition point and the state of the unsteady boundary-layer were measured using eight closely-spaced, hot-film sensors (HFS). The measurements show that:
(i) Reduced frequency has a pronounced effect on the variations of the transition point.
(ii) There exists a hysteresis loop in the dynamic transition location and its shape varies with the reduced frequency and mean angle-of-attack.
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Solid propellants burning enhancement using foil embedding method
01/12/2008
H. G. Darabkhanid and N. S. Mehdizadeh
The method of metal embedding is widely employed in solid propellant motors with end-burning configuration, thereby significantly improving the burning rate of the propellants. In this study, the cylindrical foil embedding method is applied to double-base solid propellant, as a new method, and the effects of the type and thickness of the foil on the burning surface, as well as the burning rate, are experimentally investigated. It is shown that by using the foil embedding method, the burning characteristics of solid propellants can be improved. Results have been compared to some available data. To the best of the author’s knowledge there are no published data available on this method.
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Comparison between blade-element models of propellers
01/12/2008
O. Gur and A. Rosen
Blade-element models are the most common models for the analysis of propeller aerodynamics, performance calculations and propeller design. In spite of their simplicity these models are very efficient and accurate. Blade-element models use the local induced velocities as an input thus they should be combined with another model in order to calculate these induced velocities. Various models are used for the calculation of the induced velocity, where the most popular ones include: momentum, simplified-momentum, lifting-line (prescribed and free wake), and vortex (McCormick and Theodorsen) models. The paper describes the various models, compares their results and discusses the advantages and disadvantages of each one. The results indicate that the Blade-element/simplified-momentum model offers very good accuracy together with high efficiency. For propeller performance calculations during steady axial flight, where most of the cross-sections do not experience stall, detailed and complicated models for calculating the induced velocities do not show advantages over the simple blade-element/simplified-momentum model,
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Dither-based compensating strategy for radome boresight error and gimbal friction
01/12/2008
Y.-C. Lin, C.-L. Lin, W.-C. Shi and S.-W. Huang
This paper proposes an effective missile radome error compensator by incorporating a nondestructive dither on the missile guidance loop to improve tracking accuracy. The compensation strategy predicts the radome slope error by introducing the dithering techniques along with band-pass filtering mechanism. A new condition is derived to ensure the guidance and control system stability while there is in the presence of the compensation error. As an application, the design methodology is extended to deal with the gimbal friction compensation problem. Simulation study confirms efficacy of our proposed approach.
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Helicopter load alleviation using active control
01/11/2008
M. Voskuijl, D. J. Walker and B. J. Manimala
This paper discusses how structural load objectives can be included in a rotorcraft flight control system design in an efficient and straightforward way using multivariable control techniques. Several research studies have indicated that pitch link loads for various rotorcraft types can reach high or even unacceptable values, both in steady state and maneuvering flight. This is especially the case for high-speed aggressive maneouvers. Pitch link loads at high-speed flight are therefore taken as a case study. A novel longitudinal control system is presented, designed to reduce helicopter pitch-link loads during high-speed longitudinal manoeuvres whilst providing a pitch attitude command attitude hold response type. The design is based on a high-order model of a helicopter representative of the UH-60 Black Hawk. New metrics are presented for the analysis of structural loads that can be used in combination with ADS-33 handling qualities requirements.
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Toward an intelligent, deterioration accommodating controller for aging turbofan engines
01/11/2008
J. A. Turso and J. S. Litt
A method for accommodating engine deterioration via a scheduled linear parameter varying quadratic Lyapunov function (LPVQLF)-based controller is presented. The LPVQLF design methodology provides a means for developing unconditionally stable, robust control of linear parameter varying (LPV) systems. The controller is scheduled on the engine deterioration index, a function of estimated parameters that relate to engine health, and is computed using a multilayer feedforward neural network. Acceptable thrust response and tight control of exhaust gas temperature (EGT) is accomplished by adjusting the performance weighting on these parameters for different levels of engine degradation. Nonlinear simulations demonstrate that the controller achieves specified performance objectives while being robust to engine deterioration as well as engine-to-engine variations.
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Performance simulation of a high-bypass turbofan with a 2D representation of the intake and fan components
01/11/2008
F. C. Mund and P. Pilidis
In conventional gas turbine performance simulation, engine components are represented by characteristics where the 3D properties of the flow fields are averaged providing key flow properties at the component interfaces. Even though a very efficient method, the simplification of 3D flows to an averaged value is not always desirable. In particular for high-bypass turbofan aero-engines, the fan generates significant pressure variations from hub to tip. These profiles are affected by the flow profile resulting from the intake where boundary layers introduce radial distortion patterns.
This study investigates a performance simulation method where the intake and fan component of a two-shaft high-bypass turbofan are represented in an axi-symmetric 2D fashion. The intake was modelled using a commercial computational fluid dynamics tool. The remaining engine components were modelled using an in-house conventional gas turbine simulation tool with a radial representation of the fan. The coordinated application of both tools required an iterative data exchange, which is described in detail.
The inclusion of the radial representation of fan and intake showed twice the effect on thrust per inlet loss at cruise conditions. It was therefore worth considering despite the significant numerical effort.
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Effect of counterflow argon plasma jet on aerodynamic drag of a blunt body at hypersonic Mach numbers
01/11/2008
D. Mahapatra, R. Sriram and G. Jagadeesh
An experimental investigation of aerodynamic drag reduction by counter flow plasma jet injection from the stagnation region of a hemispherical blunt cylinder model flying at hypersonic Mach numbers are presented. Experiments are carried out in a hypersonic shock tunnel at four different jet-to-pitot pressure ratios namely 15.3, 24.52, 72.5 and 96.67 and three supply powers, namely 1.8KW, 2.7KW and 3.6KW. The flow fields around the test model are visualised using high speed schlieren technique. Direct force measurement is also performed using a single component accelerometer balance. The weakly ionised argon plasma jet has an electron temperature around 6,400K and electron number density ~1.64 ´ 1015cm–3. With plasma jet at pressure ratio 72.5 and 1.8KW supply power the reduction in drag is found to be ~28% (more than its cold jet counter part) although the plasma jet momentum is less than its cold jet counter part.
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Conceptual design of UAV using Kriging based multi-objective genetic algorithm
01/11/2008
S. Rajagopal and R. Ganguli
This paper highlights unmanned aerial vehicle (UAV) conceptual design using the multi-objective genetic algorithm (MOGA). The design problem is formulated as a multidisciplinary design optimisation (MDO) problem by coupling aerodynamic and structural analysis. The UAV considered in this paper is a low speed, long endurance aircraft. The optimisation problem uses endurance maximization and wing weight minimisation as dual objective functions. In this multi-objective optimisation, aspect ratio, wing loading, taper ratio, thickness-to-chord ratio, loiter velocity and loiter altitude are considered as design variables with stall speed, maximum speed and rate of climb as constraints. The MDO system integrates the aircraft design code, RDS and an empirical relation for objective function evaluation. In this study, the optimisation problem is solved in two approaches. In the first approach, the RDS code is directly integrated in the optimisation loop. In the second approach, Kriging model is employed. The second approach is fast and efficient as the meta-model reduces the time of computation. A relatively new multi-objective evolutionary algorithm named NSGA-II (non-dominated sorting genetic algorithm) is used to capture the full Pareto front for the dual objective problem. As a result of optimisation using multi-objective genetic algorithm, several non-dominated solutions indicating number of useful Pareto optimal designs is identified.
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Experimental investigation on spiked body in hypersonic flow
01/10/2008
R. C. Mehta, R. Kalimuthu and E. Rathakrishnan
A spike attached to a hemispherical body drastically changes its flowfield and influences aerodynamic drag in a hypersonic flow. It is, therefore, a potential candidate for drag reduction of a future high-speed vehicle. The effect of the spike length, shape, spike nose configuration and angle-of-attack on the reduction of the drag is experimentally studied with use of hypersonic wind-tunnel at Mach 6. The effects of geometrical parameters of the spike and angle-of-attack on the aerodynamic coefficient are analysed using schlieren picture and measuring aerodynamic forces. These experiments show that the aerodisk is superior to the aerospike. The aerodisk of appropriate length, diameter and nose configuration may have the capability for the drag reduction. The inclusion of an aero disk at the leading edge of the spike has an advantage for the drag reduction mechanism if it is at an angle-of-attack, however consideration to be given for increased moment resulting from the spike is required.
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2D and 3D low frequency aerodynamics
01/10/2008
L. H. van Zyl
Unsteady aerodynamic loads on aircraft configurations are used for aeroelastic or flight dynamic analyses. The sources for deriving these loads include strip theory aerodynamics and three-dimensional panel methods. In some applications the behaviour of the unsteady air loads as the frequency approaches zero is important, and it is well known that the behaviour of strip theory aerodynamics employing the exact circulation function differs qualitatively from that of the three-dimensional panel methods such as the subsonic doublet lattice method (DLM). Theoretical results from an earlier study of the low frequency behaviour of the DLM are used here to show the relationship between the DLM and strip theory and the relationship is verified by a numerical example.
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Cold flow analysis of trapped vortex combustor using two equation turbulence models
01/10/2008
P. Selvaganesh and S. Vengadesan
A new combustor concept referred as the trapped vortex combustor (TVC) employs a vortex that is trapped inside a cavity to stabilise the flame. The cavity is formed between two axisymmetric disks mounted in tandem. TVC offers many advantages when compared to conventional swirl stabilisers. In the present work, numerical investigation of cold flow (non-reacting) through trapped vortex combustor is performed. The numerical simulation involves passive flow through TVC to obtain an optimum cavity size to trap stable vortices inside the cavity and to observe the important characteristics of TVC. One of the main objectives is to evaluate various two equation turbulence models for the aerodynamic predictions of TVC. Commercial CFD software Fluent is used for the present study. In addition to many models available, Non-linear k-w and modified k-w models are incorporated through user defined functions. Results obtained include streamlines, residence time and entrainments for all models. The reattachment length obtained by non-linear k-w model closely matches with that obtained by DNS in the case of forebody-spindle alone. Non-linear k-w model alone captures the corner vortices while all the other models failed to capture. From the entrainment characteristics study, it is inferred that the primary air needs to be injected for accommodating the decrease in oxidizer inside the cavity to obtain better performance from the TVC.
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Flight mechanics of a free-wing tilt-body aircraft
01/10/2008
K. Ro, J. W. Kamman and J. B. Barlow
The free-wing tilt-body aircraft refers to a vehicle configuration in which the wing, fuselage, and empennage are in a longitudinally articulated connection. This allows the main wing to freely rotate relative to the body, while the empennage, which is in the form of a long twin boom connected to the rear of the body, changes its incidence angle relative to the body in response to external commands. The principal advantages claimed for the configuration are short takeoff and landing capability, and reduced gust sensitivity. The aerodynamics of the free-wing tilt-body configuration has been previously studied, but analysis of its flight mechanics is limited. In this paper we present derivations of the flight dynamic equations of motion using multi-body dynamic modelling techniques, and combine the resulting equations of motion with experimental aerodynamic data to achieve a nonlinear mathematical model for flight simulation of a generic free-wing tilt-body vehicle. The mathematical model is suitable for the study of detailed dynamic characteristics as well as for model based control law synthesis. Key flight performance, and stability and control characteristics of a generic configuration are obtained from the mathematical model.
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Convergence: Commodity flight simulation and the future
01/10/2008
K. Takeda, S. J. Newman, J. Kenny and M. Zyskowski
The development of commodity flight simulation, in the form of PC game technology, continues to advance at a rapid pace. Indeed, the software industry is now being driven primarily by the requirements of gaming, digital media, and other entertainment applications. This has largely been due to the commoditisation of computer hardware, which is apparent when considering recent trends in central processing unit and graphics processor development.
The flight simulation industry has benefited from this trend of hardware commoditisation, and will continue to do so for the foreseeable future. It is, however, yet to fully realise the potential for leveraging commodity-off-the-shelf (COTS) software. In this paper the opportunities presenting themselves for the next 25 years of flight simulation are discussed, as the aviation and games software industry’s requirements converge. A SWOT (strengths-weaknesses-opportunities-threats) analysis of the commodity flight simulation software industry is presented, including flight modelling, scenery generation, multiplayer technology, artificial intelligence, mission planning, and event handling. Issues such as data portability, economics, licensing, intellectualproperty, interoperability, developer extensibility, robustness, qualification, and maintainability are addressed.
Microsoft Flight Simulator is used as a case study of how commodity flight simulation has been extended to include extensive programmatic access to its core engine. Examples are given on how the base platform of this application can be extended by third-party developers and the power this extensibility model provides to the industry.
This paper is presented to highlight particular technology trends in the commodity flight simulation industry, the fidelity that commodity flight simulations can provide, and to provide a high-level overview of the strengths and weaknesses thereof.
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An investigation into supersonic shallow swept cavity flows
01/10/2008
B. Reim, C. Panetta, E. Samanes, S. Gai, J. Milthorpe and H. Kleine
An experimental investigation was conducted to determine the flow characteristics of shallow swept cavities at a free-stream Mach number of 2. The investigation described herein focused on obtaining information on both time-averaged and time-dependent flow features. The data consisted of steady and unsteady pressure measurements as well as some surface oil and schlieren flow visualisation. The effective length-to-depth ratios l/d of cavities investigated ranged between 5·65 and 8 for shallow ‘open’ cavities and between 11·31 and 16 for ‘closed’ cavities. The cavity sweep angles were 0°, 15° and 45°. The results of the swept cavities, when compared to the datum cases of the straight (0°) cavities, showed some distinct differences. With regard to time-averaged flow characteristics, in an open swept cavity (5·65 < l/d < 8), the flow displayed quasi-open flow behaviour, distorted by the spanwise cross flow within the cavity. In the case of the closed swept cavity (11·31 < l/d < 16), flow features resembling the ‘closed’ to ‘transitional closed’ cavity flow types were seen to exist simultaneously across the span. Unsteady pressure data indicated that for an open cavity at 15° sweep angle, the discrete frequencies observed were similar to those of a straight open cavity. In contrast to this, at 45° sweep angle, the frequencies were broadband with no discrete frequency across the cavity length. For the closed cavity, the frequencies were all broadband irrespective of the sweep angle. The investigation also showed that the influence of the sweep angle on the pressure drag of the cavity strongly depends on the type of cavity flow: a sweep angle increase from 0° to 45° approximately doubled the pressure drag for an open cavity, while it led to a drag reduction of about 37% for the closed cavity.
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A timed method for the estimation of aeroplane take-off and landing distances
01/10/2008
G. B. Gratton
This paper describes a method by which, without the use of external personnel or equipment, take-off and landing distances of an aeroplane may be estimated. An error analysis for the method, allowing determination of outcome accuracy, is also shown. The method is validated through use of flight test results from two certification programmes, one on a light aeroplane, and one on a microlight aeroplane.
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Dimensionless analysis of the unstart boundary for 2D mixed hypersonic inlets
01/09/2008
J. Chang , D. Yu , W. Bao and L. Qu
Inlet unstart boundary is one of the most important issues of the hypersonic inlet and is also the foundation of the protection control of a scramjet. To solve this problem, the 2D internal steady flow of a 2D mixed internal/external compression hypersonic inlet was numerically simulated at different freestream conditions and backpressures with a RANS (Reynolds-Averaged Navier-Stokes) solver using a RNG (Renormalisation Group) k-ε turbulence model, and two different inlet unstart phenomena were analysed. The dimensional analysis method was introduced to find the essence variables describing the inlet unstart boundary based on “numerical experimental” data in this paper. The dimensionless pressure ratios of the forebody and isolator were analysed respectively. The results show that the unstart boundary of the 2D mixed hypersonic inlet is determined by M0, α and Re0. Pressure ratio π increases with M0 increasing, and it increases firstly and decreases then with α increasing. Pressure ratio π increases with Re0 increasing. Re0 (Re0 < 2 × 107) has a major effect on π and Re0 (Re0 > 2×107) has little effect on π.
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Distributed parameter control arithmetic for an axisymmetrical dual-mode scramjet
01/09/2008
C. Tao, Y. Daren and B. Wen
Dual-mode scramjet is one of the candidates for hypersonic flight propulsion system which will be used in wide range of flight Mach numbers from 4 to 12 or higher, wherein dual-mode scramjet should be well designed to be suitable for subsonic/supersonic combustion operation according to the flight conditions. Therefore this system is required to operate in a finite number of operational modes that necessitate robust, stable, and smooth transitions between them by which selective operability of supersonic/subsonic combustion modes and efficient combustor operation in these modes may be realised. A key issue in making mode transition efficient and stable is mode transition control. The major problem in mode transition control is the handling of the various flow and combustion coupling effects of dual-mode scramjet whose physical states are spatially coupled and whose governing equations are partial differential equations. Involving these distributed parameter issues, our basic idea is using the shape control theory to study the control problems of mode transition for dual-mode scramjet with the aim of achieving the desirable design properties and increasing control reliabilities. This specific approach is motivated by the promise of novel techniques in control theory developed in recent years. Concrete control arithmetic of this approach, such as shape control model, sensitivity analysis and gradient-based optimisation procedure, are given in this paper. Simulation results for an axisymmetric, wall-injection dual-mode scramjet show the feasibility and validity of the method.
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Conceptual design assessment of a suborbital tourist space access vehicle
01/09/2008
B. Chudoba, G. Coleman, X. Huang and P. A. Czysz
Space transportation remains in the pioneering stages. What might this century bring if we had a ‘railroad to space’ that embodied the characteristics of the transcontinental undertaking? The X-33 and Venture Star projects were one attempt to achieve the characteristics of that transcontinental railroad. There are others, here and in other countries, but perhaps we need to begin with a smaller first step, a small, commercial reusable rocket with ballistic ascent to space altitude with a hypersonic glider return? Our challenge in space today is to develop vehicles that are in continuous use, maintained and operated on a fixed schedule despite weather or environmental hazards, which move payloads not only into space but back again. The X PRIZE was a $10 million prize awarded to Scaled Composites as the first privately financed spaceship that launched the equivalent of three persons to an altitude of at least 100 kilometers on two consecutive flights within two weeks. What about an analogous vehicle that flies two or three times a week, every week for a number of years? A major difference is that this challenge is to be accomplished without government support or government developed vehicles. The aerospace vehicle design (AVD) Laboratory team at the University of Texas at Arlington is developing a generic space access vehicle (SAV) design synthesis environment with focus on the conceptual design phase. The AVD Lab has applied elements of this toolbox to the study of a tourist aerospace vehicle under a grant from Rocketplane Limited, Inc. The development of a low-cost tourist vehicle based on the adaptation of a Learjet 25/35/45 series aircraft is the focus of this paper.
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Systematic review of the impact of emissions from aviation on current and future climate
01/09/2008
K. Takeda, A. L. Takeda, J. Bryant and A. J. Clegg
Aviation emissions have an impact on the global climate, and this is consequently an active area of research worldwide. By adapting replicable and transparent systematic review methods from the field of evidence-based medicine, we aim to synthesise available data on the effects of aviation emissions on climate. From these data, we aim to calculate lower and upper bounds for estimates of the effect of aviation on climate in an objective manner.
For the systematic review an appropriate protocol was developed and applied by two independent reviewers, to identify research that met the inclusion criteria. These included all aviation types, original research studies, climate models with aviation as a specific component, with outcomes for emissions, radiative forcing, global warming potential and/or surface temperature changes. These studies were prioritised and data extracted using a standard process. The 35 studies reviewed here reported radiative forcing, global warming potential and/or temperature changes as outcomes, allowing direct comparisons to be made.
Tabulated results and a narrative commentary were provided for overall effects on climate, and the individual effects of carbon dioxide, water, contrails, cirrus clouds, ozone, nitrogen oxides, methane, soot and sulphur oxides. Lower and upper bounds for these effects, and their relative contributions compared to overall radiative forcing and surface temperature changes, have been described.
This review shows that the most recent estimates for the contribution of aviation to global climate are highly dependent on the level of scientific understanding and modelling, and predicted scenarios for social and economic growth. Estimates for the future contribution of aviation to global radiative forcing in 2015 range from 5·31% to 8·04%. For 2050 the estimates have a wider spread, from 2·12% to 17·33%, the latter being for the most extreme technology and growth scenario. These global estimates should be considered within the context of uncertainties in accounting for the direct and indirect effects of different contributions. Variations between lower and upper bounds for estimates of radiative forcing are relatively low for carbon dioxide, around 131% to 800% for cirrus clouds effects, and 1,044% for soot. Advances in climate research, particularly in the area of contrail and cloud effects, has led to some revision of the 1999 IPCC estimates(1), and demonstrates that the research community is actively working to further understand the underlying science.
The approaches assumptions, limitations and future work were discussed in detail. We have demonstrated how the systematic review methodology can be applied to climate science, in a replicable and transparent manner.
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Experimental study of overexpanded co-flowing jets
01/09/2008
H. Sharma, A. Vashishtha E. Rathakrishnan and P. Lovaraju
An experimental investigation was carried out to find the effect of an annular co-flow jet on the primary supersonic jet from Mach 2 nozzle at different levels of overexpansion. In this study, a convergent-divergent circular nozzle of exit Mach number 2, surrounded by an annular convergent circular nozzle with an annular gap of 4.4mm was used. Nozzle pressure ratios (NPRs) 3, 4, 5, 6, 7 are investigated for overexpanded states of the primary jet and NPR 8 is investigated for almost correctly expanded state. The centreline pressure distributions were taken at all NPRs for both with and without co-flow case, to investigate the supersonic core extent and mixing activity in the jet field. In the radial direction pitot pressure at different axial locations at all NPRs for both the cases are measured to find the jet development and shadowgraph visualisation of jet structure was done to visualise the shock structure in near-field. It is found that the co-flow acts as mixing inhibitor at all levels of overexpansion for Mach 2 nozzle.
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System integration of high intensity energy subsystems – a thermal management challenge
01/08/2008
D. M. Pratt and D. Moorhouse
Current and future Air Force weapons systems lack the necessary power and cooling capacity to provide full systems level capability as a result of energy and thermal management limitations. Cooling capacity of fuel is already fully utilised leaving little room for additional cooling needs. Additionally, increasing speed, power, and miniaturisation of future systems continue to stress any thermal management capability that we can now deliver. Thus, the focus of this paper is a conceptual assessment of the key energy and thermal management technologies to meet the future energy challenges. It presents an overview of the current state of the art and also possible future research.
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A circulation control actuator for flapless flight control
01/08/2008
M. V. Cook, A. Buonanno and S. D. Erbslöh
Trailing edge blowing over a Coanda surface has been utilised as a circulation control mechanism for increasing the lift of an aircraft wing. Typically, high energy air is blown from a narrow spanwise slot over the rounded trailing edge of a wing and the air supply is modulated to effect a degree of lift control on the wing. This configuration produces an aerodynamic force in a uni-directional sense only. An alternative novel flow control actuator is described which utilises a simple variable geometry Coanda surface with upper and lower spanwise blowing slots to achieve fully proportional bi-directional control in the manner of a conventional flap. A prototype device has been wind-tunnel tested and is shown to have substantially linear response characteristics and to be as efficient as an equivalent flap surface. The performance of a flow control actuator suitable for small UAV applications is described.
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Capturing requirements for tiltrotor handling qualities – case studies in virtual engineering
01/08/2008
G. D. Padfield
Handling qualities are expressed as requirements at the interface of the pilot and the machine. In this way, the key functionality questions facing the design engineer are seen from the perspective of the interaction of the human pilot with the aircraft system and the environment in which it operates. In this paper, the author takes a ‘virtual engineering’ approach to handling qualities, emphasising the importance of conducting ‘requirements capture’ and preliminary design as an iterative process. When stretched capabilities are required, this approach minimises the risk to finding appropriate technology solutions, through developing explicit relationships between capability and design parameters, thus facilitating fully informed trade studies and predictions. Case studies from the development of a civil tiltrotor aircraft are presented that show how the difficult challenges facing the designer first need to be structured in terms of HQ predictions and assignments. This then provides the basis on which handling qualities improvements can be constructed within the multidisciplinary context of rotorcraft engineering.
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Prediction of laminar, transitional and turbulent flow regimes, based on three-equation k-w turbulence model
01/08/2008
R. Taghavi-Zenouz, M. Salari and M. Etemadi
A recently developed transitional model for boundary-layer flows has been examined on a flat plate and the well-known S809 wind turbine blade. Proposed numerical model tries to simulate streamwise fluctuations, induced by freestream turbulence, in pre-transitional boundary-layer flows by introducing an additional transport equation for laminar kinetic energy term. This new approach can be used for modeling of transitional flows which are exposed to both the freestream turbulence intensity and streamwise pressure gradient, which are known as the most dominant factors in occurrence of transition. Computational method of this model is based on the solution of the Reynolds averaged Navier-Stokes (RANS) equations and the eddy-viscosity concept. The model includes three transport equations of laminar kinetic energy, turbulent kinetic energy and dissipation rate frequency. The present model is capable of predicting either natural or bypass transitional mechanisms, which may occur in attached boundary-layer flows. In addition, the model can simulate transition in the separated free shear layers and the subsequent turbulent re-attachment to form a laminar separation bubble. Flat plate was exposed to different freestream turbulence intensities and streamwise pressure gradients. Wind turbine blade was examined under two different Reynolds numbers, with one of them suitable for the occurrence of laminar separation bubbles on its surfaces. To evaluate the performance of this new model in resolving transitional boundary-layer flows, final results have been compared to those obtained through application of conventional turbulence models. Comparison of final results for the flat plate and the S809 aerofoil with available experimental data show very close agreements.
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Technological aspects of gas turbine and fuel cell hybrid systems for aircraft: a review
01/08/2008
M. Santin, A. Traverso and A. Massardo
The objective of this work is to make an overview of opportunities and issues related to the aeronautical application of solid oxide fuel cell hybrid systems. The great interest on fuel cells comes from their capacity of producing electric energy with high efficiency at low pollutant production. The application of these systems as full-time auxiliary power units is an interesting alternative in a future scenario, which is supposed to include a More Electric Aircraft and more restrictive environmental standards. A review of the technological aspects of this application is presented. The physical models found in literature were investigated and the results were compared and discussed.
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A study of various energy- and exergy-based optimisation metrics for the design of high performance aircraft systems
01/08/2008
V. Periannan, M. R. von Spakovsky and D. J. Moorhouse
This paper shows the advantages of applying exergy-based analysis and optimisation methods to the synthesis/design and operation of aircraft systems. In particular, an Advanced Aircraft Fighter (AAF) with three subsystems: a Propulsion Subsystem (PS), an Environmental Control Subsystem (ECS), and an Airframe Subsystem – Aerodynamics (AFS-A) is used to illustrate these advantages. Thermodynamic (both energy and exergy based), aerodynamic, geometric, and physical models of the components comprising the subsystems are developed and their interactions defined. Off-design performance is considered as well and is used in the analysis and optimisation of system synthesis/design and operation as the aircraft is flown over an entire mission.
An exergy-based parametric study of the PS and its components is first presented in order to show the type of detailed information on internal system losses which an exergy analysis can provide and an energy analysis by its very nature is unable to provide. This is followed by a series of constrained, system synthesis/design optimisations based on five different objective functions, which define energy-based and exergy-based measures of performance. The former involve minimising the gross takeoff weight or maximising the thrust efficiency while the latter involve minimising the rates of exergy destruction plus the rate of exergy fuel loss (with and without AFS-A losses) or maximising the thermodynamic effectiveness.
A first set of optimisations involving four of the objectives (two energy-based and two exergy-based) are performed with only PS and ECS degrees of freedom. Losses for the AFS-A are not incorporated into the two exergy-based objectives. The results show that as expected all four objectives globally produce the same optimum vehicle. A second set of optimisations is then performed with AFS-A degrees of freedom and again with two energy- and exergy-based objectives. However, this time one of the exergy-based objectives incorporates AFS-A losses directly into the objective. The results are that with this latter objective, a significantly better optimum vehicle is produced. Thus, an exergy-based approach is not only able to pinpoint where the greatest inefficiencies in the system occur but appears at least in this case to produce a superior optimum vehicle as well by accounting for irreversibility losses in subsystems (e.g., the AFS-A) only indirectly tied to fuel usage.
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Balloons, airships and kites lighter than air past, present and future
01/07/2008
J. Folkes
One hundred years on from the advent of aeronautics at Queen Mary, University of London, developments in lighter than air technology have progressed at a somewhat slower pace than the technology for heavier than air. Innovations afforded by the ‘discovery’ of helium, the development of the modern day hot air balloon and the application of new materials have all contributed to today s technical innovations. A review is given of the past history of lighter than air, a note is made of the current state of the art and a brief overview of future applications is discussed. The author s personal experience in long distance gas balloon flights is mentioned.
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The generation of sound in turbulent motion
01/07/2008
G. M. Lilley
Abstract
The present paper reviews and discusses the physical mechanisms of noise generation and reduction in turbulent flows with their applications towards aircraft noise reduction at takeoff and on the approach. This work began in 1948 when Lilley undertook an experimental investigation into the source of jet noise as a necessary precursor to finding methods for the reduction of high speed jet engine noise on civil jet airliners. Westley and Lilley completed this experimental programme in 1951, which included the design of a range of devices for high speed jet noise reduction. It was about this time that similar studies on jet noise were being started elsewhere and in particular by Lassiter and Hubbard in USA. The major contribution to the subject of turbulence as a source of noise came from Sir James Lighthill’s remarkable theory in 1952. In spite of the difficulties attached to theoretical and experimental studies on noise from turbulence, it is shown that with the accumulated knowledge on aerodynamic noise over the past 50 years, together with an optimisation of aircraft operations including flight trajectories, we are today on the threshold of approaching the design of commercial aircraft with turbofan propulsion engines that will not be heard above the background noise of the airport at takeoff and landing beyond 1-2km, from the airport boundary fence.
It is evident that in the application of this work, which centres on the physical mechanisms relating to the generation of noise from turbulence and turbulent shear flows, to jet noise, there is not one unique mechanism of jet noise generation for all jet Mach numbers. This author in this publication has concentrated on what appears to be the dominant mechanism of noise generation from turbulence, where the mean convection speeds of the turbulence are subsonic. The noise generated at transonic and supersonic jet speeds invariably involves extra mechanisms, which are only briefly referred to here.
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Computational aeroacoustics: The low speed jet
01/07/2008
E. J. Avital, M. Alonso and V. Supontisky
ABSTRACT
Low speed circular, elliptic and planar jets are investigated computationally for basic sound generation and hydrodynamics. The jets are assumed to be incompressible and are simulated using the large eddy simulation (LES) approach. The emitted sound is calculated using Lighthill’s acoustic analogy. Two formulations are used, Lighthill’s stress tensor formulation and Powell’s vortex sound formulation. A new boundary correction for Powell’s formulation is developed in order to account for the finite size of the computational domain. Low to moderate Reynolds number jets are simulated. Good agreement with known hydrodynamic results is achieved. This includes the nature of the transition process, e.g. enhanced mixing and axis switching in the elliptic jet and in some statistical results. The new boundary correction for Powell’s formulation proves to be vital in order to achieve good agreement with Lighthill’s formulation. Some success in high frequency prediction at least for the circular and elliptic jets is achieved in terms of getting the expected asymptotic behaviour. Both formulations show that the elliptic jet noise level is mildly lower than the circular jet noise level. Good to very good agreement is achieved in terms of directivities and frequency spectra with known results for the various jets.
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Influence of the height of the vortex generators in the control of shock-induced separation of the boundary layers
01/07/2008
G. S. Cohen and F. Motallebi
Abstract
Experiments have been conducted to assess the effects that sub-boundary-layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary-layer separation. The freestream Mach number and Reynolds number were M = 1·45 and 15·9 × 106/m, respectively. Detailed measurements of a fully developed, flat plate turbulent boundary layer were used in order to assess the performance of ten different SBVG configurations. The SBVG performance was assessed by comparing total pressure profiles measured upstream of separation and downstream of reattachment. Static pressure distributions, near surface total pressure distributions, oil flow visualisation and Schlieren photographs were also used. The effect of SBVG height was investigated. The results show the largest SBVGs with height, h = 55%δ, provided the greatest static pressure recovery and maximum mixing. However, the shock pressure rise (wave drag) was highest for this case.
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Transitional separation bubbles and unsteady aspects of aerofoil stall
01/07/2008
N. D. Sandham
Abstract
A time-accurate solution method for the coupled potential flow and integral boundary-layer equations is used to study aerofoils near stall, where laboratory experiments have shown high-amplitude low-frequency oscillations. The laminar-turbulent transition model incorporates an absolute instability formulation, which allows the transition process in separation bubbles to be sustained in the absence of upstream disturbances, in agreement with recent direct numerical simulations. The method is demonstrated to capture large scale flow oscillations with Strouhal numbers and amplitudes comparable to experiments. The success of this particular physical model suggests that bubble bursting is primarily due to a potential-flow/boundary-layer interaction effect, in which relatively simple models of boundary layer transition and turbulence suffice to describe the key phenomena.
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One hundred years of aeronautics in East London
01/07/2008
J. A. D. Ackroyd, L. Bernstein and F. W. Armstrong
1.0 INTRODUCTION
This paper celebrates the centenary of Queen Mary College’s involvement in aeronautics, a celebration with a unique distinction since it was this College’s immediate forebear which was the first British higher education institution to begin teaching and research in this subject. Thus the emphasis is on the early years from 1907 until the 1950s, a period ripe for recording before it recedes beyond living memory, but also the period during which the degree course in aeronautical engineering became firmly established and its parent Department acquired its reputation for research. Section 2.0 gives a brief history of the College’s origins in the East London College. Subsequent sections deal with the foundation of the aeronautical laboratory there, from which the aeronautical department grew, and the activities of the two men who led these developments, A.P. Thurston and N.A.V. Tonnstein who changed his name to Piercy.
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Introduction to the Queen Mary College 100th anniversary of teaching aeronautics special Issue of The Aeronautical Journal
01/07/2008
F. Motallebi
In September 2007 and in memory of Albert Peter Thurston who established
the formal teaching of aeronautics in the United Kingdom, a twoday
conference was held at Queen Mary College. The themes of the
conference were loosely related to the first public lecture given by A.P.
Thurston in 1909: ‘Flying Machines (heavier than air type)’; ‘Balloons,
Airships and Kites’; and ‘The Mechanics Principles of Flight’. This
special issue includes some of the papers presented at this conference.
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On the aerodynamics of the Gloster E28/39 – a historical perspective
01/06/2008
B. J. Brinkworth
ABSTRACT
As commissioned to demonstrate the feasibility of jet propulsion, the E28/39 needed to exceed the performance of contemporary fighters. But Carter, the chief designer, took the opportunity to look further ahead, and devised an aircraft in which the onset of compressibility effects was taken into account from the beginning of the design. Successful operation over a wide speed range required a shrewd synthesis of previous experience and practice with uncertain material emerging from the research domain. The resulting aircraft showed no significant aerodynamic vices, requiring only minor modifications from its first flight to its participation in diving trials, that took it into hitherto unexplored regions of high subsonic speed. It proved to be fully worthy of its pivotal role at the beginning of a new era in aeronautics.
The aerodynamic features of Carter’s design are reviewed in relation to the limited state of knowledge at the time. Drawing upon fragmented material, much not previously published, this study enlarges upon, and in places amends, previous accounts of this notable machine.
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The role of drag prediction in combat aircraft design and development
01/06/2008
J. B. Newton
ABSTRACT
This paper gives an overview of combat aircraft drag prediction in the context of the overall design and development process.
Following a brief summary of the author’s experience in this field, the importance of drag prediction during initial configuration design is discussed, emphasising the need for the drag aerodynamicist to develop a good understanding of the other aerodynamic disciplines involved, as well as an appreciation of the of the total design process encompassing structural design, propulsion integration and systems installation.
A brief description is given of typical simplified prediction methods used in initial design, followed by an example of drag synthesis procedures based on wind-tunnel test and analysis, illustrating the need for good understanding of test techniques and the requirements of other aerodynamic disciplines.
Some future challenges are identified, requiring continual involvement in research and methods development programmes.
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Air traffic safety: Continued evolution or a new paradigm?
01/06/2008
P. Brooker
Abstract
Air traffic management (ATM), covering (e.g.) air traffic control and airspace structures, is the part of the aviation system that is most likely to be developed through new paradigms. ATM safety has improved over the decades for many reasons, from better equipment to additional safety defences. However, ATM safety targets, improving on current performance, are now extremely demanding. What are the past and current methodologies for ATM risk assessment; and will they work effectively for the kinds of future systems that people are now imagining and planning? How will system designers/operators assure safety with traffic growth and operational/technical changes that are more than continued evolution from the current system? What are the design implications for ‘new paradigms’, such as the USA’s ‘Next Generation Air Transportation System’ (NextGen) and Europe’s Single European Sky ATM Research Programme (SESAR)? Achieving and proving safety for NextGen and SESAR is an enormous challenge, and will need to cover system resilience, human and automation issues, software/hardware performance/ground/air protection systems. There will be a need for confidence building programmes regarding system design/resilience, e.g. human-in-the-loop simulations with ‘seeded errors’.
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Linear theory of optimum hot air balloon performance – application to Titan
01/06/2008
R. D. Lorenz
ABSTRACT
We develop a simple theory for hot air balloon performance with fixed
thermal power and linear heat transfer to the environment, applicable to
low-temperature situations such as Titan’s atmosphere. The theory
results in a closed-form solution and it is shown that an optimum
balloon diameter exists – the maximum payload is achieved when the
envelope mass and payload mass are equal. It is also shown simply that
the floating mass for a given power has a stronger sensitivity to heat
transfer coefficient than to the envelope specific mass. A hot air
balloon on Titan with a ~2kW heat source could loft a theoretical
maximum payload of ~195kg or ~100kg with appropriate margins.
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Generic stability and control for aerospace flight vehicle conceptual design
01/06/2008
B. Chudoba, G. Coleman, H. Smith and M. V. Cook
ABSTRACT
The recent period has been filled with exceptionally interesting developments and advances, resulting in high-performance conventional and non-conventional manned and unmanned aircraft. Although those vehicles seem to comply well with specific mission performance requirements, one is still confronted with an apparent weakness to reliably stabilise and control throughout the flight envelope. Since the provision of satisfactory stability and control characteristics invariably compromises flight performance, it becomes essential to identify and integrate performance-optimal stability and control design solutions early during the flight vehicle definition phase. In particular, the conceptual design of integrated control effectors for advanced aircraft is far from being trivial. Never before have we been presented with such tremendous wealth of specialised data and information suitable for detail design of controls. In contrast, never before has it been necessary to approach any one of the primary design disciplines still as entirely ad hoc and inconsistent as in the case of designing controls during the conceptual design phase. This need initiated the development of a configuration independent (generic) stability and control methodology capable of sizing primary control effectors of fixed wing subsonic to hypersonic designs of conventional and unconventional, symmetric and asymmetric configuration layouts. This paper summarises the methodology concept and demonstrates its versatility and validity by analyzing selected stability and control characteristics of the Northrop YB-49 flying wing.
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Aircraft gust load estimation due to atmospheric turbulence under different flight conditions
01/06/2008
E. N. Abdulwahab and C. Hongquan
Based on power spectral technique and Lyapunov approach, methodology to determine the vertical gust load on aircraft encountering atmospheric turbulence under different flight conditions is presented in this paper. Modified longitudinal short period aircraft equations of motion to reflect gust inputs are solved. Family of five linear dynamics models of increasing gust excitation complexity are developed to describe the normal load factor throughout an aircraft due to vertical gust. These models (except Model 2) give a rapid estimation of normal load factor in case complete data are not readily available. Numerical model constructed for a Boeing 747 jet transport is solved to illustrate the results. These results show that Model 5 exhibits higher frequency contents when compared with other models under different flight conditions. The normal load factor of aircraft is estimated at different probabilities of not exceeding the corresponding load factor value based on statistical technique. The Models 1, 3, 4 and 5 predict the load factor with maximum 5% error when compared with Model 2 which considered all gust penetration effects. Finally, the results show a good agreement with the published work in load factor determination, at different probabilities of not exceeding this value when encountering a turbulent vertical gust.
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Whirl flutter analysis of prop-rotors using unsteady aerodynamics reduced-order models
01/05/2008
M. Gennaretti and L. Greco
The prediction of this aeroelastic phenomenon is an urgent need of the designer and requires devoted numerical tools. This work examines the influence of the accuracy of the aerodynamic modelling on whirl flutter analysis, with particular attention to those models that can conveniently be applied to preliminary design and control purposes. Considering a simple pylon/prop-rotor structure, the aeroelastic instability boundaries are identified by 2D quasi-steady and 2D unsteady aerodynamics theories, along with a 3D unsteady, potential flow BEM solver. A methodology for deriving reduced-order models from unsteady aerodynamic solutions is used. The numerical investigation highlights that the accuracy of the aerodynamic solver included in the analysis may be of crucial importance. The use of 2D aerodynamic models does not always guarantee conservative stability predictions, and this is particularly true for three-bladed rotors where a fully 3D unsteady solver coupled with a wake alignment algorithm seems to be necessary.
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Monitoring of aircraft landing gear structure
01/05/2008
R. K. Schmidt
Landing gear structure is developed predominantly using safe life
design criteria. Health monitoring and structural prognosis
techniques for landing gear cannot focus on crack detection;
techniques for determining input loads and calculating damage or
methods for directly measuring material damage must be employed.
This paper will discuss Messier-Dowty’s research into structural
monitoring over the past several years. Principally, direct damage
detection systems and load monitoring systems will be discussed.
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Genetic optimisation of a neural network damage diagnostic
01/05/2008
G. Manson, E. Papatheou and K. Worden
This paper presents an automated optimisation procedure for the feature selection stage of a previously proposed structural health monitoring methodology using a genetic algorithm. The same diagnostic is used in the attempt to progress up the levels of damage detection to location and severity. It was validated experimentally on a Gnat aircraft wing. An artificial neural network is used as a classifier and the work is compared with the previous selection strategy based on engineering judgement.
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Numerical simulation of rime ice accretions on an aerofoil using an Eulerian method
01/05/2008
Y. Cao, Q. Zhang and J. Sheridan
Based on two-phase flow theory, an Eulerian method to simulate rime ice accretions on an aerofoil has been developed. The SIMPLE (semi-implicit method for pressure linked equations) algorithm on a collocated grid is employed to solve the governing equations for the airflow. In order to simulate droplets impinging on an aerofoil, a permeable wall is proposed to solve the governing equations for supercooled droplets. The collection efficiency and impingement limits are obtained from the droplets’ flowfield. The process of ice accretion is simulated using the assumption that ice accumulates layer-by-layer and the ice shape is predicted with the assumption that ice grows in the direction normal to the aerofoil surface. The rime ice accretions on a NACA0012 aerofoil at 0° and 4° angles-of-attack have been investigated and there is agreement between the simulated results and previously published experimental data. The change of the pressure coefficient along the iced aerofoil is also analysed.
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Active sensing of impact damage in composite sandwich panels by low frequency Lamb waves
01/05/2008
C. Soutis and K. Diamanti
ABSTRACT
The development of a robust non-destructive system to detect and monitor the extent of damage in carbon fibre reinforced plastics (CFRP) during service life is a key problem in many practical applications, especially in the aircraft industry. The lack of such technique has severely limited the potentially extensive use of composite materials. In this study a cost and time effective inspection strategy for in-service health monitoring of composites is demonstrated using the fundamental anti-symmetric A0 Lamb mode at frequencies of 15-20kHz. In principle, this method involves analysis of the transmitted and/or reflected wave after interacting with the test-piece boundaries or discontinuities (defects). In the present work, the applicability of the technique to composite sandwich structures is explored and defects of critical size are successfully detected.
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Indirect aircraft structural monitoring using artificial neural networks
01/05/2008
S. C. Reed
ABSTRACT
From necessity, military aircraft often operate in a highly fatigue damaging environment and history has shown in lost lives and aircraft the consequences of failure to appreciate fully the usage environment. The need for robust and cost effective structural usage monitoring of military aircraft to ensure operations are conducted within acceptable levels of risk is paramount. Furthermore, increased economic pressures require ever-inventive methods to be employed to maximise the lives of military fleets; structural usage monitoring will be a key asset in this drive. A highly cost effective indirect structural health and usage neural network (SHAUNN) monitoring system is proposed. A SHAUNN uses regression relationships determined by artificial neural networks to predict stresses, strains, loads, or fatigue damage from flight parameters. Within this paper the development of a SHAUNN monitoring system is described. Flight parametric data, captured during Operational Loads Measurement of the Royal Air Force Dominie TMk1 aircraft have been used to predict stresses at the key structural location in the wing, using mapping relationships determined by artificial neural networks. A framework for the development of the SHAUNN monitoring system is discussed and the basic architecture of the multilayer perceptron artificial neural network is described. It is concluded that this technology could provide the basis for an accurate, cost-effective structural usage monitoring system and further work to investigate the prediction of ground –based stresses in the wing is recommended.
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Structural health monitoring systems – benefits and airworthiness issues
01/05/2008
P. A. Lloyd
In recent years there has been an increasing interest in the application of advanced structural monitoring systems to aircraft structures. A great deal of research effort has, and is being directed towards technologies that can detect damage and estimate its significance. In this paper the benefits of deploying such systems are discussed and illustrated with quantitative estimates where these are available. It is concluded that significant benefits should accrue from their use, but that a number of outstanding technical issues remain which include the realistic verification of performance and reliability. The impact on aircraft airworthiness is also considered and it is suggested that while no significant new issues emerge, considerable work will need to be done to qualify systems, and that this is unlikely to be worthwhile unless the expected benefits can be assured.
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Interchanging simulation databases with third parties using SEDRIS
01/04/2008
R. Harris
Successful, seamless interchange of simulation databases has long proved surprisingly difficult to achieve. Numerous technical difficulties, arising from the different environmental representations used by different simulation systems, have proved to be only one facet of this difficulty. Often such problems are in fact the result of more fundamental underlying issues, such as the mathematical relationships between different co-ordinate systems. Logistical issues, and collaborative aspects of database interchange between different groups or companies, also contribute to the problems.
Thales has encountered many of these issues over the years in generating a range of databases for its simulation systems. These databases are required to correlate closely with other sensor systems, in particular the visual, but it is often the case that these other systems are third party products, using databases modelled by companies other than Thales. In these circumstances, the strategy used by Thales to generate its databases has typically been to derive them directly from the visual database. This has involved directly processing the visual database, extracting relevant geometry and attribution and formatting it for use by the Thales simulation systems. Historically, such visual databases have been provided by third parties using the SIF/HDI interchange format and imported directly into the Thales database generation toolset. While generating such derived databases in this way has been achieved successfully, many interchange issues referred to above were encountered and needed to be addressed.
When the need arose to replace SIF/HDI, the opportunity was taken to seek a replacement that would not only provide better representational capabilities but also address many of the wider, non-technical issues as well. Analysis of a variety of formats was undertaken and SEDRIS emerged as by far the strongest contender. Not only did it provide the best all round support for existing data representation requirements, it also gave good support for addressing wider interchange issues and offered a variety of opportunities to enhance the database generation toolset, both during initial development and over time.
This paper will discuss experiences using SEDRIS in this context. It will examine the basic representational requirements that needed to be met and the interchange problems that were to be overcome. The ways in which SEDRIS was seen to address these problems will be considered, along with the other advantages SEDRIS offered. Experiences developing SEDRIS software and interchanging databases using SEDRIS will also be described, including some lessons learned concerning both the use of SEDRIS and database interchange in general.
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Aerodynamic load characterisation of a low speed aerofoil using particle image velocimetry
01/04/2008
B. W. van Oudheusden, E. W .F. Casimiri and F. Scarano
Particle image velocimetry (PIV) measurements of the flow around a wing section are employed as a basis for non-intrusive aerodynamic mean loads characterisation, providing sectional lift, drag and pitching moment. The technique relies upon the application of control-volume approaches in combination with the deduction of the pressure from the PIV experimental data through application of the momentum equation. The treatment can also be applied when the flow is unsteady; in that case time-mean loads are obtained from velocity statistics, through the use of Reynolds-averaged formulation of the governing equations. The procedure was applied in the experimental investigation of a NACA 642A015 aerofoil, in which the PIV approach is validated against standard pressure-based methods (surface pressure distribution and wake rake). The chord Reynolds number considered in the investigation ranges between 1 - 7 ´ 105. In addition, the consistency and potential performance of the method was assessed by means of synthetic velocity field data obtained from a numerical flow simulation.
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What price supersonic speed? an applied market research case study Part 2
01/04/2008
B. Chudoba, A. Oza, G. Coleman and P. A. Czysz
The first supersonic business jet to enter the market will not face its competition from rival supersonic designs under development. Its true competitors are the then current generation of highly evolved high-subsonic business jets when compared on economic grounds. For a price tag of $1m for the new conception of very light jets, ranging up to $45m for the highest-performing ‘race-horse’-like corporate jets, this breed of aircraft is able to accommodate the needs of most executives, VIPs, officials, from corporate transportation to cargo services of civil to military origin. Understanding the state of modern business class aircraft and their market is essential in gaining base knowledge required for any supersonic business jet endeavor aiming at a prospective market. The key descriptors for this marketplace are market potential, market productivity, and market drivers, altogether being a measure for growth and consumer demand. Such common denominator is used to gain the understanding necessary to ascertain and visualise the top level implications regarding any supersonic business case. Having assembled an understanding of the key descriptors for business aviation, the study first analyses the flight operation of traditional subsonic and high-subsonic business jets. Such perceptive is then complemented with the peculiarities associated with supersonic operation, ultimately defining the supersonic solution space consisting of market viability, efficiency, and overall flight performance. Consequently, a vehicle development strategy and mission specification are suggested for the first generation of supersonic business jets (SSBJ) and supersonic cargo jets (SSCJ).
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Development of mechanical guidance actuators for a supersonic projectile
01/04/2008
K. C. Massey, J. McMichael, T. Warnock and F. Hay
In this paper, the results of a series of experiments funded by DARPA to determine the feasibility of using small actuators to provide directional control for a supersonic projectile are presented. Controlling the flight of the projectile was accomplished by taking advantage of complex shock-boundary-layer interactions produced by mechanical devices. Experimental tests were conducted at GTRI to screen several control concepts and actuator locations. Further experiments were conducted on a scale projectile in a supersonic stream to investigate the rise time of the forces. Several different mechanical actuators were tested which served to provide guidance for future actuator designs. CFD results were also used to predict the results in flight as well as gain insights into the fluid mechanics involved. Flight tests of a Mach 4 round proved the viability of the guidance actuator.
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Lateral-directional controller design using a pilot model and flight simulator experiments
01/04/2008
H. Tokutake, J. Fujinaga and Y. Miura
A new controller design method of lateral-directional dynamics is proposed. This method is based on the formulated pilot model, and the controller is designed so that the pilot-aeroplane system attains the desired requirements. Robust stabilities and handling qualities can be taken into account. The proposed method was applied to B747 dynamics, and flight simulator experiments were performed, and the designed controller was verified.
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Simulation interoperability — where are the challenges?
01/03/2008
B. N. Tomlinson
This paper will discuss and review the nature of simulation interoperability. It will analyse the scope of interoperability in terms of basic intercommunication features (technical interoperability), fitness for purpose (functional interoperability) and suitability for use in distributed training (training interoperability). Only technical interoperability has received close attention, through DIS and HLA standards. Other aspects still present many challenges. The ability to create a common ‘outside world’ database is frequently cited as the dominant component and principal challenge in any discussion of interoperability. While this is often true, this paper identifies how interactions among all participants in the shared operational space (‘battlespace’) should be the starting point in defining interoperability, these interactions of course being dictated by the training requirement. Interactions are accomplished through ‘sensors’, which could be the human eye, night vision goggles (NVGs), radios, data links, radar, FLIR etc. Comprehensive interoperability demands comparable levels of modelling among all participants, including the effect of the environment (whether terrain or meteorology) on the performance of each simulator’s sensor suite. The paper will identify these significant effects and discuss where simulation technology is challenged and needs to advance, particularly in the context of mission simulation of future joint (Air/Land/Maritime) operations. The paper concludes with some discussion of the way ahead, including how guidelines based on experience could augment the use of standards.
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Converging towards synthetic environment interoperability
01/03/2008
B. Lalonde
The evolution of simulators from proprietary hardware platforms to affordable commercial-off-the-shelf (COTS) platforms has gone on for the past 15 years and is now nearly complete. Nevertheless, past efforts to standardise simulator synthetic environments (SE) have only been partially successful and have engendered considerable aggravation for users in need of creating content that can be deployed to distributed full-mission simulators. This paper provides a detailed description of the SE generation pipeline and the reasoning that has modeled its evolution over the past few decades. The arrival of digital multi-spectral high-resolution satellite imagery and highly capable visual systems now requires orders of magnitude more storage and processing than equivalent databases just a few years ago. These factors are threatening the equilibrium of the SE pipeline and are becoming important elements affecting SE interoperability, portability and re-usability. Past design trade-offs and compromises, appropriate at the time, must now be re-examined along with all SE-related processes, starting from ingestion of raw source data right through to the processing by the simulator devices. Clearly, greater standardisation is needed within the simulation community and a comprehensive, open SE representation would palliate to the many challenges we now face. To this end, this paper provides a checklist of the characteristics for a future ‘ideal’ SE representation and evaluates four emerging synthetic environment initiatives against this extensive checklist.
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What price supersonic speed? A design anatomy of supersonic transportation Part 1
01/03/2008
B. Chudoba, G. Coleman, A. Oza and P. A. Czysz
The first generation of supersonic commercial transportation has seen three serious attempts to arrive at an economically and environmentally viable aircraft. The US B2707-200/300 design was cancelled early before a prototype could emerge; the Russian Tu-144 design succeeded to become the first supersonic transport but spanned only a few years of restricted airline service; the Anglo-French Concorde endured more than 27 glamorous airline service years until the last of its species was retired on 30 August 2003. This first generation was followed by a second generation of supersonic commercial transport projects in the time period between 1986 until about 1999, designs which did not proceed towards the production hardware stage. This study critically examines the anatomy of two generations of supersonic commercial transport design failures and successes in order to arrive at lessons learned free of ‘wishful thinking’. The design conditions leading to the identification of the product ‘solution space’ for an economically and environmentally acceptable supersonic commercial transport are discussed. Having assembled an understanding of the product metrics valid for supersonic commercial transports, the paper then provides an outlook for the first generation of supersonic corporate and cargo jet projects. This first generation of supersonic business jet (SSBJ) and supersonic cargo jet (SSCJ) projects spans a period of nearly two decades of development, starting from 1988 until today. The present study identifies that the product development metrics of this class of aircraft is radically different compared to the metrics valid for supersonic commercial transports. The challenges in VIP transportation and dedicated freight transportation at supersonic speeds are portrayed leading to two principal trains of thought targeting the development of the first supersonic business jet and/or supersonic cargo jet hardware: the development based on a new airframe, and alternatively the development based on an existing airframe.
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Dynamic performance investigations of a turbojet engine using a cross-application visual oriented platform
01/03/2008
K. G. Kyprianidis and A. I. Kalfas
This paper presents the development of visual oriented tools for the dynamic performance simulation of a turbojet engine using a cross-application approach. In particular, the study focuses on the feasibility of developing simulation models using different programming environments and linking them together using a popular spreadsheet program. As a result of this effort, a low fidelity cycle program has been created, capable of being integrated with other performance models. The amount of laboratory sessions required for student training during an educational procedure, for example for a course in gas turbine performance simulation, is greatly reduced due to the familiarity of most students with the spreadsheet software. The model results have been validated using commercially available gas turbine simulation software and experimental data from open literature. The most important finding of this study is the capability of the program to link to aircraft performance models and predict the transient working line of the engine for various initial conditions in order to dynamically simulate flight phases including take-off and landing.
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Morphing skins
01/03/2008
C. Thill, J. Etches, I. Bond, K. Potter and P. Weaver
A review of morphing concepts with a strong focus on morphing skins is presented. Morphing technology on aircraft has found increased interest over the last decade because it is likely to enhance performance and efficiency over a wider range of flight conditions. For example, a radical change in configuration, i.e. wing geometry in flight may improve overall flight performance when cruise and dash are important considerations. Although many morphing aircraft concepts have been elaborated only a few deal with the problems relating to a smooth and continuous cover that simultaneously deforms and carries loads. It is found that anisotropic and variable stiffness structures offer potential for shape change and small area increase on aircraft wings. Concepts herein focus on those structures where primary loads are transmitted in the spanwise direction and a morphing function is achieved via chordwise flexibility. To meet desirable shape changes, stiffnesses can either be tailored or actively controlled to guarantee flexibility in the chordwise (or spanwise) direction with tailored actuation forces. Hence, corrugated structures, segmented structures, reinforced elastomers or flexible matrix composite tubes embedded in a low modulus membrane are all possible structures for morphing skins. For large wing area changes a particularly attractive solution could adopt deployable structures as no internal stresses are generated when their surface area is increased.
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Some features of steady separated flow from low speed to hypersonic
01/02/2008
S. L. Gai
Steady non-vortex shedding base flow behind a bluff body is considered. Such a flow is characterised by the flow separation at the trailing edge of the body with an emerging shear layer which reattaches on the axis with strong recompression and recirculating flow bounded by the base, the shear layer, and the axis.
Steady wake flows behind a bluff body at low speeds have been studied for more than a century (for example, Kirchhoff(1); Riabouchinsky(2)). Recently, research on steady bluff body wake flow at low speeds has been reviewed and reinterpreted by Roshko(3,4). Roshko(3) has also commented on some basic aspects of steady supersonic base flow following on from Chapman(5) and Korst(6) analyses.
In the present paper, we examine the steady base flow features both at low speeds and supersonic speeds in the light of Roshko’s model and expand on some further aspects of base flows at supersonic and hypersonic speeds, not covered by Roshko.
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A model for solar powered aircraft preliminary design
01/02/2008
E. Rizzo and A. Frediani
Solar powered aircraft are becoming more and more interesting for future long endurance missions at high altitudes, because they could provide Earth monitoring, telecommunications, etc. without any atmospheric pollution and, hopefully in the near future, with competitive costs compared with satellites. The research activities carried out till now have been mainly focused on flying wings or conventional aircraft configurations, with a great emphasis on the technological aspects. The present paper aims to define a mathematical model for solar powered aircraft preliminary design, valid independently of the aerodynamic configuration. A preliminary analysis is carried out in order to simulate Helios and the results are compared with those available from the flights of this aircraft. The proposed mathematical model is used also to compare four different aircraft configurations, namely: a flying wing, a conventional aircraft, a twin boom aircraft and a biplane aircraft. The results obtained are discussed in the paper and an optimum aircraft is analysed.
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A low-Reynolds-number one-equation model of turbulence
01/02/2008
M. Elkhoury
This work proposes an improved form of Menter’s single-equation eddy viscosity transport model. The new transport equation follows from the transformation of the k-e closure that includes the Yap-correction term, which is known to improve the (k-e) model’s prediction in adverse pressure gradient flows. The damping functions of the (low-Reynolds-number) LRN model are constructed using the ingenious approach of Baldwin and Barth. Hence, the model provides the correct wall-limiting behaviour of turbulence. Furthermore, the destruction term is modified to better account for non-equilibrium anisotropy effects. An assessment of the present proposed model against experiments, as well as Menter and Spalart-Allmaras (SA) turbulence models is provided via several boundary layer computations. Good agreement with experimental data is indicated, which merits the model to be considered for further refinement.
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Flight parameter based fatigue analysis approach for a fighter aircraft
01/02/2008
J. A. Tikka
This paper describes a flight parameter based fatigue life analysis approach, which is developed for the Finnish Air Force F-18 fighters. It produces a flight specific fatigue life estimate for structural details using flight parameter data stored by each aircraft. Artificial neural networks are used to model structural response of analyzed details as a function of flight parameters. The analysis development is based on strain gauge data from 25 flights of an instrumented aircraft. The results show a satisfactory accuracy for the fatigue life estimates and prove the concept level analysis capability. The average difference between measured and modelled fatigue life is 21% for the fuselage bulkhead and 30% for the leading edge flap’s hinge area. The total differences in the Finnish Air Force average usage are extremely small, being –2% for the bulkhead and +2% for the leading edge flap.
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Dynamic inflow modelling for
01/01/2008
Y. Murakami and S.S. Houston
The dynamic inflow model is a powerful tool for predicting the induced velocity distribution over a rotor disc. On account of its closed form and simplicity, the model is especially practical for studying flight mechanics or for designing control systems for helicopters. Scant attention has, however, been paid so far in utilising the dynamic inflow model to analyse an autorotating rotor, which is different from a powered rotor in the geometric relation between the direction of the inflow and the rotor disc. Autorotation is an abnormal condition for helicopters, but for gyroplanes it is the normal mode of operation. Therefore the theoretical discussion on an autorotating rotor is of importance not only to improve the understanding of present gyroplanes, but also in the development of new gyroplanes and to analyse the windmill-brake state of helicopters. Dynamic inflow modelling is reviewed from first principles, and this identifies a modification to the mass flow parameter. A qualitative assessment of this change indicates that it is likely to have a negligible impact on the trim state of rotorcraft in autorotation, but a significant effect on the dynamic inflow modes in certain flight conditions. This is confirmed by numerical simulation, although considerable differences only become apparent for steep descents with low forward speed. It is concluded that while modification of the mass flow parameter is perhaps mathematically accurate, for practical purposes it is required only in a limited area of the flight envelope of autorotating rotorcraft.
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Experimental and computational investigation into the use of co-flow fluidic thrust vectoring on a small gas turbine
01/01/2008
A. Banazadeh, F. Saghafi M. Ghoreyshi and P. Pilidis
This paper presents the application of a relatively new technique of fluidic thrust-vectoring (FTV), named Co-flow, for a small gas-turbines. The performance is obtained via experiment and computational fluid dynamics (CFD). The effects of a few selected parameters including the engine throttle setting, the secondary air mass-flow rate and the secondary slot height upon thrust-vectoring performance are provided. Thrust vectoring performance is characterised by the ability of the system to deflect the engine thrust with respect to the delivered secondary air mass-flow rate. The experimental study was conducted under static conditions in an outdoor environment at Cranfield University workshop that was especially designed for this purpose. As part of this investigation, the system was modelled by CFD techniques, using Pointwise’s Gridgen software and the three-dimensional flow solver, Fluent. Also, Cranfield’s gas-turbine performance code (TurboMatch) was utilised to estimate boundary conditions for the CFD analysis with respect to the integrated nozzle. The presented technique is easy-to-use approach and offers better result for thrust-vectoring problems than previously published works. Experimental results do show the overall viability of the blowing slot mechanism as a means of vectoring the engine thrust, with the current configuration. Computational predictions are shown to be consistent with the experimental observations and make the CFD model a reliable tool for predicting Co-flow fluidic thrust-vectoring performance of similar systems.
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Impacts of low-pressure (LP) compressor’s deterioration of a turbofan engine upon fuel-usage of a military aircraft
01/01/2008
M. Naeem
Some in-service deterioration in any mechanical device, such as an aircraft’s gas-turbine engine, is inevitable. However, its extent and rate depend upon the qualities of design and manufacture, as well as on the maintenance/repair practices followed by the users. Deterioration of an engine normally results in the engine seeking a different steady operating-point relative to that for an engine without any deterioration. The variation in engine’s steady operating point leads to changes in the specific fuel consumption (SFC) and/or fuel flow (FF). Any rise in SFC and/or FF and thereby the increased quantity of fuel required is of prime importance in military aviation.
For a military aircraft’s mission-profiles (consisting of several flight-segments), using a bespoke computer simulations, the consequences of low-pressure compressor’s deterioration of an aero-engine upon the weight of the fuel that has to be carried and consumed are predicted. This will help in making wiser management decisions (such as whether to remove an aero-engine from the aircraft for maintenance or to continue using it with some changes in aircraft’s mission profile). Hence improved engine utilization can be achieved, so resulting in lower overall life-cycle costs.
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Periodic transonic flow and control
01/01/2008
S. Raghunathan, J.M. Early, C. Tulita, E. Benard and J. Quest
The current understanding of periodic transonic flow is reviewed briefly. The effects of boundary-layer transition, non-adiabatic wall conditions and modifications to the aerofoil surface geometry at the shock interactions on periodic transonic flow are discussed. Through the methods presented, it is proposed that the frequency of periodic motion can be predicted with reasonable accuracy, but there are limitations on the prediction of buffet boundaries associated with periodic transonic flows. Several methods have been proposed by which the periodic motion may be virtually eliminated, most relevantly by altering the position of transition fix, contouring the aerofoils surface or adding a porous surface and a cavity in the region of shock interaction. In addition, it has been shown that heat transfer can have a significant effect on buffet.
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Method for aerodynamic unsteady forces time calculations on an F/A-18 aircraft
01/01/2008
D. E. Biskri and R. M. Botez
In this paper, a new original method based on the least squares method is presented for the conversion of unsteady aerodynamic forces from frequency into Laplace domain, in which the error is written in an analytical form as a function of the Laplace variable, similar to the analytical form of the aerodynamic forces calculated by use of the least squares method. This method is applied on an F/A-18 aircraft (14 symmetric and 14 anti-symmetric modes) for one Mach number and for a set of 14 reduced frequencies. Two different types of results are obtained and analysed: aerodynamic force approximations in the Laplace domain and flutter speeds and frequencies values. For a better comparison of these results, different lag term numbers are used. Results obtained by this new method are better in terms of execution speed and precision than the results obtained by use of the least squares method.
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Flight data reduction methodology for performance evaluation and comparison of model-following adaptive control laws
01/12/2007
M. G. Perhinschi and M. R. Napolitano
Even small differences in atmospheric and/or flight conditions can potentially impact significantly the evaluation of the performance of the control laws and prevent a correct comparison, especially in the case of reduced size aircraft (autonomous or remotely piloted). Consistent deterministic control inputs can only be guaranteed through some form of computer-based on-board excitation system. In this paper, a methodology is proposed for flight data reduction with the purpose of accounting for non-homogeneous atmospheric conditions and inconsistent pilot inputs. The method is developed for the specific purpose of comparing model-following adaptive control laws. Performance evaluation parameters based on angular rate tracking errors are defined and used for the comparison. As a result of this approach, an additive correction is applied to the angular rate measurements to compensate for non-homogeneous turbulence effects. A multiplicative correction factor is applied to the angular rate tracking error to take into account non-identical pilot inputs. The procedure is validated with simulation and flight data obtained in the process of designing a set of fault tolerant control laws based on non-linear dynamic inversion with neural network augmentation for the reduced size WVU YF-22 aircraft model.
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A review of supersonic business jet design Issues
01/12/2007
H. Smith
Key issues relating to the Supersonic Business Jet (SBJ) concept are reviewed with the intent to assess the readiness of enabling technologies and hence the concept itself. The multidisciplinary nature of aircraft design precludes an in-depth analysis of each specific aspect, which could individually be the subject of a separate discipline review, hence an overview is presented.
The review looks at the market, environmental issues, with particular reference to the sonic boom phenomenon & solutions, technological issues, including prediction methods, flight testing, systems, certification and interested aerospace companies and design organisations.
It is apparent that the need to reduce the sonic boom signature is vital if the vehicle is to be permitted to operate over land and hence be economically viable. It is clear that sonic boom acceptability requirements must be set if resources are to be effectively focused and designs are to converge. Despite this challenge, considerable investment is aimed at de-risking many of the enabling technologies and raising readiness levels. Many technologies are moving beyond theoretical and numerical analysis into the experimental and flight test domains. Collaboration between the civil and military sectors is increasing.
Clearly, supersonic air travel is not an efficient means of personal conveyance; however, concerns for the environment are difficult to balance against the ‘value of time’ benefits offered by the SBJ concept. Air travel, of which this is a specialised form, is important to the global economy. Continued effort in the areas of human factors, customer demand and certification & requirements would be beneficial.
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An idea of distributed parameter control for scramjet engines
01/12/2007
Y. Daren, C. Tao and B. Wen
Scramjet engines are used under extreme temperatures and with wide range of Mach numbers from 3 to 8 or higher and have shown different control properties from other airbreathing engines. New control problems involving distributed parameter control have been found concerning investigations of the control of scramjet engines whose physical states are spatially interacted and whose governing equations are partial differential equations. The work of this paper is based on the application of distributed parameter control conception to study the control problems of scramjet engines with the aim of achieving the desirable design properties and increasing control reliability. A new control idea based on shape control theory is put forward to realise the distributed parameter control of scramjet engines with the preconditions of proper space dimension and frequency-domain simplification. Simulation results and theoretic analysis for an axisymmetric, wall-injection scramjet engine show the feasibility and validity of the control idea.
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Three-dimensional tensile stress concentration in countersunk rivet holes
01/12/2007
A. Bhargava and K. N. Shivakumar†
A detailed and accurate three-dimensional finite element stress analysis was conducted on countersunk rivet holes in a plate subjected to tension loading. The analysis included a wide range of countersunk depths, plate thicknesses, countersunk angles and plate widths. The study confirmed some of the previous results, addressed their differences, provided many new results, and investigated countersunk angle and width effects. Using the detailed FE results and the limiting conditions, a design equation for stress concentration was developed and verified.
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Flow control with active dimples
01/11/2007
S. Dearing, S. Lambert and J. Morrison
The long-term goal is to design and manufacture optimal ‘on-demand’ vortex generators, ‘dimples’ that can produce vortices of prescribed strength and duration for the real-time control of aerodynamic flows that are either undergoing transition or are fully turbulent, attached or separating. Electro-active polymers (EAP) are ideal for a dimple control surface, offering high strain rate, fast response, and high electromechanical efficiency. EAP can also be used as the basis of a resistanc – or capacitance – change pressure sensor, development of which has just begun. In terms of manufacture, inkjet printing of EAP also offers a paradigm shift such that a monolithic control surface is a very real possibility. Important features for integration into a control system are robustness and a predictable, repeatable motion. With these objectives in mind, the suitability of EAP-based actuators is assessed both mechanically and aerodynamically. The ultimate goal is to integrate these devices, along with shear-stress and pressure sensors and distributed control, also under development, into a flexible ‘smart skin’ which could be incorporated into an airframe structure. The response of a laminar boundary layer to forcing is investiagted using mechanical dimples.
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Large-eddy simulation of separated flow over a swept wing with approximate near-wall modelling
01/11/2007
N. Li and M. A. Leschziner
The paper investigates, by means of a simulation methodology, the flow separating from a 40 degrees backward-swept wing at 9 degrees incidence and Reynolds number of 210,000, based on the wing-root chord length. The Simulation corresponds to LDA, PIV and suction-side-topology measurements for the same geometry, conducted by other investigators specifically to provide validation data. The finest block-structured mesh contains 23·6 million nodes and is organised in 256 blocks to maximise mesh quality and facilitate parallel solution on multi-processor machines. The near-wall layer is resolved, to a thickness of about y+ = 20, by means of parabolised URANS equations that include an algebraic eddy-viscosity model and from which the wall-shear stress is extracted to provide an unsteady boundary condition for the simulation. The numerical solution is in good agreement with the experimental behaviour over the 50-70% inboard portion of the span, but the simulation fails to resolve some complex features close to the wing tip, due to a premature leading-edge vortex breakdown and loss in vortex coherence. The comparisons and their discussion provide useful insight into various physical characteristics of this complex separated wing flow.
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Reducing environmental impacts of aviation with innovative air traffic management technologies
01/11/2007
V. Williams, R. B. Noland, A. Majumdar, R. Toumi†, W. Ochieng and J. Molloy
Commercially-driven air traffic management (ATM) innovations typically aim to increase air space capacity and/or reduce delays. Here, their potential application for environmental mitigation is discussed. Both carbon dioxide (CO2) and non-CO2 climate impacts are considered, as are noise and air quality issues. We outline the technological, scientific and political barriers to an integrated approach to applying ATM technologies to environmental mitigation. These issues highlight the need to improve comparison and prioritisation of the emissions and effects of aviation.
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Experimental and computational study of unsteady hypersonic cavity flows
01/11/2007
S. Creighton and R. Hillier
This paper presents a combined experimental and computational study of annular cavities on a semi-angle cone in a Mach 8·9 flow. A range of cavity length-to-depth ratios has been considered, and a parameter has been determined that distinguishes between ‘weak oscillations’ and ‘strong oscillations’ of the cavity flow. Essentially the work identifies the transition from the case where the flow can be regarded as ‘pure cavity flow’ to that where the flow behaviour is tending towards that of a ‘spiked blunt body’. The CFD simulations also suggest that, for a certain range of cavity scale, the limiting cavity flow state depends upon the flow initialisation process; it may be weak or strongly oscillating.
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Prediction of drag and lift of wings from velocity and vorticity fields
01/11/2007
G. Zhu, P. W. Bearman and J. M. R. Graham
The present paper continues the work of Zhu et al(9). The closed-form expressions for the evaluation of forces on a body in compressible, viscous and rotational flow derived in the previous paper have been extended to different forms. The expressions require only a knowledge of the velocity field (and its derivatives) in a finite and arbitrarily chosen region enclosing the body. The equations are implemented on three-dimensional inviscid flows over wings and wing/body combinations. Further implementation on three-dimensional viscous flows over wings has also been investigated.
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Experimental and computational study of unsteady hypersonic cavity flows
01/11/2007
S. Creighton and R. Hillier
This paper presents a combined experimental and computational study of annular cavities on a semi-angle cone in a Mach 8·9 flow. A range of cavity length-to-depth ratios has been considered, and a parameter has been determined that distinguishes between ‘weak oscillations’ and ‘strong oscillations’ of the cavity flow. Essentially the work identifies the transition from the case where the flow can be regarded as ‘pure cavity flow’ to that where the flow behaviour is tending towards that of a ‘spiked blunt body’. The CFD simulations also suggest that, for a certain range of cavity scale, the limiting cavity flow state depends upon the flow initialisation process; it may be weak or strongly oscillating.
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Remarks on the nonlinear dynamics of a typical aerofoil section in dynamic stall
01/11/2007
U. Galvanetto, J. Peirò and C. Chantharasenawong
We use standard tools of the theory of dynamical systems such as phase plots, bifurcation diagrams and basins of attraction to analyse and understand the dynamic behaviour of a typical aerofoil section under dynamic stall conditions. The structural model is linear and the aerodynamic loading is represented by the Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this model are non-linear and non-smooth, therefore we have integrated the equation of motion using a Runge-Kutta-Fehlberg (RKF45) algorithm equipped with event detection. We perform simulations of the motion for a range of Mach numbers and show that the model is very sensitive to small variations. This is evidenced by the presence in the bifurcation diagram of co-existing attractors or, in other words, by the existence of more than one steady-state motion for a given Mach number. The mechanisms for the appearance and disappearance of the co-existing attractors are elucidated by analysing the evolution of their basins of attraction as the Mach number changes.
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Effect of plunging amplitude on the performance of a wind turbine blade section
01/11/2007
M. R. Soltani and F. Rasi Marzabadi
Extensive low speed wind-tunnel tests were conducted to study the unsteady aerodynamic behaviour of an airfoil sinusoidally oscillating in plunge. The experiments involved measuring the surface pressure distribution over a range of amplitudes, H = ±5 to ±15cm. In addition, steady state data were acquired and were used to furnish a baseline for further analysis and comparison. The model was oscillated with a constant reduced frequency, k = 0·058, at three mean angles of attack of 0º, 10º and 18º.The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. The plunging displacements were transformed into the equivalent angle-of-attack. Variations of the pressure coefficients and aerodynamic loads with the equivalent angle-of-attack showed strong sensitivity to the plunging amplitude and also to the mean angles-of-attack.
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Modelling the interaction of helicopter main rotor and tail rotor wakes
01/10/2007
T. M. Fletcher and R. E. Brown
The mutual interaction between the main rotor and tail rotor wakes is central to some of the most problematic dynamic phenomena experienced by helicopters. Yet achieving the ability to model the growth and propagation of helicopter rotor wakes with sufficient realism to capture the details of this interaction has been a significant challenge to rotorcraft aerodynamicists for many decades. A novel computational fluid dynamics code tailored specifically for rotorcraft applications, the vorticity transport model, has been used to simulate the interaction of the rotors of a helicopter with a single main rotor and tail rotor in both hover and low-speed quartering flight, and with the tail rotor rotating both top-forward and top-aft. The simulations indicate a significant level of unsteadiness in the performance of both main and tail rotors, especially in quartering flight, and a sensitivity to the direction of rotation of the tail rotor. Although the model thus captures behaviour that is similar to that observed in practice, the challenge still remains to integrate the information from high fidelity simulations such as these into routine calculations of the flight dynamics of helicopters.
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Scramjets
01/10/2007
M Smith
The supersonic combustion ramjet, or scramjet, is the engine cycle most suitable for sustained hypersonic flight in the atmosphere. This article describes some of the challenges facing scramjet designers, and the methods currently used for the calculation of scramjet performance. It then reviews the HyShot 2 and Hyper-X flight programs as examples of how sub-scale flights are now being used as important steps towards the development of operational systems. Finally, it describes some recent advances in three-dimensional scramjets with application to hypersonic cruise and multi-stage access-to-space vehicles.
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Survivability of helicopter with individual blade primary control failure
01/10/2007
R. Ganguli, B. Jehnert, J. Wolfram and P. Voersmann
The effect of actuator damage on a helicopter rotor with an IBC based primary control system is studied. Such a system eliminates the swashplate and can be accomplished by trailing-edge flaps, active twist or full authority IBC, especially with smart material actuators. Damage to the collective, longitudinal and lateral cyclic are simulated for one blade, both individually and in combinations ranging from partial damage to complete failure. Numerical results are obtained using a dissimilar blade aeroelastic analysis based on finite elements in space and time for hover and forward speed conditions. It is found that the helicopter can be trimmed for all cases with all three controls having failed on the blade with actuator damage thereby showing that the IBC actuated rotor can survive an actuator failure and can be reconfigured by the pilot using the controls on the other blades. However, in case the collective fails and the longitudinal cyclic is present, there are problems in achieving trim at high damage levels at high forward speeds. Physical explanations of this phenomenon are given. The response (especially flap) for the damaged rotor blades can become high and 1/rev and 2/rev are transmitted by the reconfigured rotor to the hub. Results show that IBC based primary controls provide redundancy which can improve the survivability of a helicopter in case of actuator failure in one blade.
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Estimation of lateral-directional parameters using neural networks based modified delta method
01/10/2007
S. Singh and A. K. Ghosh
The aim of the study described herein was to develop and verify an efficient neural network based method for extracting aircraft stability and control derivatives from real flight data using feed-forward neural networks. The proposed method (Modified Delta method) draws its inspiration from feed forward neural network based the Delta method for estimating stability and control derivatives. The neural network is trained using differential variation of aircraft motion/control variables and coefficients as the network inputs and outputs respectively. For the purpose of parameter estimation, the trained neural network is presented with a suitably modified input file and the corresponding predicted output file of aerodynamic coefficients is obtained. An appropriate interpretation and manipulation of such input-output files yields the estimates of the parameter. The method is validated first on the simulated flight data using various combinations and types of real-flight control inputs and then on real flight data. A new technique is also proposed for validating the estimated parameters using feed-forward neural networks.
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An optimal-fuzzy two-phase CLOS guidance law design using ant colony optimisation
01/10/2007
H. Nobahari and S. H. Pourtakdoust
The well-known ant colony optimisation (ACO) meta-heuristic is applied to optimise the parameters of a new fuzzy command to line-of-sight (CLOS) guidance law. The new guidance scheme includes two phases, a midcourse and a terminal phase. In the first phase, a lead strategy is utilised which reduces the acceleration demands. A proportional derivative (PD) fuzzy sliding mode controller is used as the main tracking controller of the first phase. Moreover, a supervisory controller is coupled with the main tracking controller to guarantee the missile flight within the beam. In the terminal phase, a pure CLOS guidance law without lead angle is utilised. For this phase, a new hybrid fuzzy proportional-integral-derivative (PID) fuzzy sliding mode controller is proposed as a high precision tracking controller. The parameters of the proposed controllers for the first and the second phases are optimised using ACO. In this regard, the recently developed continuous ant colony system (CACS) algorithm is extended to multi-objective optimisation problems and utilised to optimise the parameters of the pre-constructed fuzzy controllers. The performance of the resulting guidance law is evaluated at different engagement scenarios and compared with the well-known feedback linearisation method. The comparison is also made in the presence of measurement noise.
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Some analytical and numerical solutions for the safe turn manoeuvres of agricultural aircraft – an overview
01/09/2007
B. Rasuo
In this paper, a theoretical study of the turn manoeuvre of an agricultural aircraft is presented. The manoeuvre with changeable altitude is analyzed, together with the, effect of the load factors on the turn manoeuvre characteristics during the field-treating flights. The mathematical model used describes the procedure for the correct climb and descent turn manoeuvre. For a typical agricultural aircraft, the numerical results and limitations of the climb, horizontal and descending turn manoeuvre are given. The problem of turning flight with changeable altitude is described by the system of differential equations which describe the influence of the normal and tangential load factors on velocity, the path angle in the vertical plane and the rate of turn, as a function of the bank angle during turning flight. The system of differential equations of motion was solved on a personal computer with the Runge-Kutta-Merson numerical method. Some analytical and numerical results of this calculation are presented in this paper.
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‘Greener’ civil aviation using air-to-air refuelling – relating aircraft design efficiency and tanker offload efficiency
01/09/2007
R. K. Nangia
The aircraft industry, as a whole, is striving to limit its impact on the environment. Improved engine design and operation may offer a reduction in emissions of a few percent. More efficient air traffic control (ATC) may offer a limited reduction in overall fuel burn. Improvements in aerodynamic design and materials available (e.g. on A350XWB, B787) might achieve a few percent increases in efficiencies. The use of alternative fuels is some way off. The ACARE objectives present a stiff challenge.
Our recent studies have shown that air-to-air-refuelling (AAR), well established in military circles, introduced to civil aircraft operations would provide fuel savings of the order of 30% – 40%. AAR will allow smaller (3,000nm range), more efficient (greener) aircraft, operating from shorter runways, to fulfil long-range route requirements. In addition, the ‘safety-net’ afforded by the availability of AAR will enable a host of hitherto borderline technologies to be accepted and utilised in future aircraft designs. Laminar flow will provide fuel savings and increased efficiency in its own right provided it is enabled within a civil AAR environment. Similarly, supersonic transport becomes an acceptable economic option.
As a result of our previous publication in the RAeS The Aeronautical Journal, November 2006(1), a few more interesting aspects have emerged with regard to tanker design and operation and the magnitude of the fuel off-loads available and relating them to overall fuel savings and gains in payload range efficiency (PRE).
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Developments in RF simulator technology
01/09/2007
M. Pywell
Technology developments in radar frequency simulators of the type used to verify the performance of complex electronic warfare systems are described. The successful verification of this performance prior to combat use is a necessary pre-requisite of military platform survivability and mission success. These simulators and associated modelling and analysis tools have enabled a major shift during the last 15 years from expensive and limited flight trials to repeatable laboratory and anechoic chamber tests, although they will never totally supplant those trials. Most limitations of the early days of many-channel simulators, 25 years ago, have been resolved or adequately and – as importantly – affordably mitigated, largely enabled by computing power increases. Limitations remain that will, within affordability constraints driven by Defence Ministries world-wide, prevent perfect simulation (‘emulation’) and the attendant, tantalising but utopian goal of laboratory and chamber test results that precisely match those from flight test and combat.
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On the benefits of lower Mach number aircraft cruise
01/08/2007
A. Filippone
The paper reviews the issue of cruise Mach number and addresses the benefits of operating subsonic commercial aircraft at speeds below the long-range cruise speed. The case considered is the flight of transport aircraft for flight segments up to 1,000nm. It is shown that the fuel burned is decreased by as much as 1×8% on a nominal 1,000nm stage length for operation around the long-range cruise Mach number, or below. This is achieved at a cost of a marginal delay on each flight segment (less than three minutes). The longer flight time is likely not to affect the daily operation of the aircraft. The fuel saving is compounded, because the gross take-off weight (GTOW) is recalculated to take into account the reduced fuel consumption at each flight segment. The analysis into the environmental benefits includes the reduction in,andemissions, and the heat released in the high atmosphere. Sensitivity analyses are carried out on the take-off weight, on the aerodynamic coefficients, on the transonic drag rise and the weight uncertainty. It is predicted that the optimal operation of the example aircraft over a nominal 1,000nm route can reduce the fuel consumption by as much as 150,000kg per year in comparison with an operation at the long-range Mach number. The aircraft model has a maximum take-off weight of 170,000kg and is powered by two GE CF6-80C2 engines.
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A review of some current research on pressure sensitive paint and thermographic phosphor techniques
01/08/2007
K. Kontis
The paper discusses the development and application activities within the Aero-Physics and Measurement Technology Laboratory at the University of Manchester on pressure sensitive paint and thermographic phosphor optical imaging systems for gas dynamic applications. It provides a brief review of the basic principles, fundamental theory, properties, chemical characteristics and bonding technologies associated with the two systems. A number of case studies are presented, which exhibit the range of applicability, limitations and potential for further development of the technologies.
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Application of synthetic jet actuators for the modification of the characteristics of separated shear layers on slender wings
01/08/2007
M. Watson, A. J. Jaworski and N. J. Wood
This paper presents an experimental investigation related to controlling the unsteady characteristics of the separated shear layers occurring over highly swept wings, and in particular focuses on application of synthetic jet actuators for modification of unsteady dynamic loading on the wing surface due to the phenomenon referred to as vortex breakdown (vortex burst).
In the post burst flow region the surface pressure measurements reveal the presence of certain characteristic spectral peaks that are thought to represent the presence of a spiralling filament of vorticity inside the expanded vortex that is known to be present in the burst flow over swept wings.
This paper details an investigation into how the use of an array of 18 discrete synthetic jet actuators, distributed along the leading edge of a delta wing with a 60° sweep angle, can be used to alter the spectral content of this unsteadiness and reduce the level of unsteady pressure found in the post-burst region toward the wing trailing edge by up to 40%.
Measurements of the surface pressure spectral distributions over the wing are presented together with PIV measurements of the vortex cross-section, conducted in the successive planes parallel to the wing trailing edge. Additional surface flow visualisation indicates that the effect of the actuators on the leading edge boundary layer is to induce local separation delays close to each actuator orifice, which introduce ‘ripples’ into the shear layer as it separates. The results obtained are used to formulate an interpretative hypothesis attempting to explain the mechanisms responsible for modification of the spectral content and the level of excitation measured on the wing surface.
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Three-dimensional tensile stress concentration in countersunk rivet holes
01/08/2007
Anil Bhargava and Kunigal N. Shivakumar†
A detailed and accurate three-dimensional finite element stress analysis was conducted on countersunk rivet holes in a plate subjected to tension loading. The analysis included a wide range of countersunk depths, plate thicknesses, countersunk angles and plate widths. The study confirmed some of the previous results, addressed their differences, provided many new results, and investigated countersunk angle and width effects. Using the detailed FE results and the limiting conditions, a design equation for stress concentration was developed and verified.
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The Victoria University of Manchester’s contributions to the development of aeronautics
01/08/2007
J. A. D. Ackroyd
This issue of the Aeronautical Journal celebrates the 50th anniversary of the foundation of the Honours Degree Course in Aeronautical Engineering at the Victoria University of Manchester. The following article therefore describes the aeronautical research and teaching activities of that university up to its recent amalgamation with the University of Manchester Institute of Science and Technology (UMIST) to form the present-day University of Manchester. This juncture provides a further justification for recording the Victoria University’s achievements.
Both the Victoria University and UMIST had their roots in the nineteenth century although, apart from the relatively brief period of the First World War, neither of them was particularly involved in aeronautics until after the Second World War. However, as Sections 6.0-10.0 seek to demonstrate, thereafter the Victoria University’s involvement became considerable. The preceding Sections describe the origins of the Victoria University and UMIST and, in the case of the former institution, the subsequent activities of its staff and graduates in engineering and mathematics which, although not always specifically aeronautical in content, nonetheless had a profound influence on the development of the aeronautical sciences.
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Towards a full two dimensional gas turbine performance simulator
01/07/2007
V. Pachidis, P. Pilidis, L. Marinai, I. and Templalexis
In commercially available gas turbine performance simulation tools, individual engine components are typically represented with non-dimensional maps of experimental or default data. In those cases where actual component characteristics are not available and default characteristics are used instead, conventional tools can deviate substantially at off-design and transient conditions. Similarly, when real component characteristics are available, conventional engine cycle simulation tools can not predict the performance of the engine at other than nominal conditions satisfactorily, or account for the impact of changes in component geometry.
This study looked into the full integration of two-dimensional streamline curvature component models with a low fidelity cycle program. Firstly, the obtained engine performance was compared against the one calculated based on default component characteristics. As a second case study, a range of flight Mach numbers and angles of attack were examined together with the effect of three different intake lip geometries on the performance of a notional, two-spool, low-bypass ratio, military engine. Two-dimensional models were used in the engine cycle analysis to provide a more accurate, physics- and geometry-based estimate of intake and fan performances.
The analysis carried out by this study demonstrated relative changes in the predicted engine performance larger than 1%. For briefness, representative results are presented and discussed in this paper for one flight Mach number and angle of attack setting. More importantly, this research effort established the necessary methodology and technology required towards a full, two-dimensional engine cycle analysis at an affordable computational resource in the very short term.
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A static compressible flow model of synthetic jet actuators
01/07/2007
H. Tang and S. Zhong
In this paper, a simple static compressible flow model for circular synthetic jet actuators is described. It is used to undertake a systematic computational investigation of the effect of changing actuator geometrical and operating parameters on the magnitude of peak jet velocity at the orifice exit of an actuator whose diaphragm displacement and frequency are allowed to vary independently. It is found that, depending on the flow conditions inside the orifice duct, the actuator may operate in two distinct regimes, i.e. the Helmholtz resonance regime and the viscous flow regime. In the Helmholtz resonance regime, the resultant synthetic jet is generated by the mass physically displaced by the oscillating diaphragm coupled with the Helmholtz resonance in the actuator. In the viscous flow regime, the Helmholtz resonance is completely damped by viscous effect such that the jet is produced by the diaphragm oscillation alone. The relationship between actuator geometrical and operating parameters at the optimum condition which yields the maximum peak jet velocity at a given diaphragm displacement is also established for these two regimes. Finally, a preliminary procedure for designing synthetic jet actuators for flow separation control on an aircraft wing is proposed.
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Dynamic gain scheduled control of a Hawk scale model
01/07/2007
T. Richardson, M. Lowenberg, C. Jones and A. Dubs
When designing flight control laws using linearisations of an aircraft model about different flight conditions, some form of scheduling of the resultant gains will often be required to implement the controller over wide operating regions. In practice, the controller gains are often scheduled against relatively slowly-varying system states such as altitude or velocity. However, it may also be desirable to schedule gains against rapidly-varying states such as angle-of-attack, thereby generating a cyclic dependence through hidden coupling terms. Previous published work at Bristol has developed a numerical method of accounting for this dependence when scheduling state feedback gains against coupled states. The resulting `dynamic gain schedule’ is shown to significantly improve the transient response of the aircraft model during rapid manoeuvring and to reduce the chances of control surface actuator position limit saturation. In this paper, the novel design process, using eigenstructure assignment, is applied to a mathematical second-order longitudinal aircraft model which represents an approximate BAe Hawk wind-tunnel model. The dynamic gain scheduled controller is shown to work extremely well in practice when applied to the closed-loop experimental rig. Despite the highly nonlinear characteristics of the model aerodynamics and tailplane actuation system, as well as unmodelled high turbulence levels, dynamic gain scheduling demonstrates stable closed loop control even in regions where the nonlinearities are such that conventional gain scheduling fails to produce a stable response.
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The representation of GT component maps using Mach numbers
01/07/2007
V. E. Kyritsis, P. Pilidis and K. Ramsden
Component maps are produced under certain environmental conditions using air as the working fluid during static ground operation. Any changes of the component characteristics when operating under different temperature conditions and/or with different working fluid are partially taken into account, because of the existence of the gas constant and the ratio of the specific heats in the non-dimensional mass flow and rotational speed. This provides a second order correction for the component characteristics, which may be adequate for the initial modeling of engines. However, for rigorous performance calculations correction factors are applied to the non-dimensional mass flow, rotational speed and pressure ratio distributions of a map, when deviations from the reference conditions under which it was extracted, are experienced. In the current study, a different approach is considered in order to eliminate the inaccuracies caused by the varying temperature and chemical composition. It makes direct use of inlet and circumferential Mach numbers based upon stagnation temperature in conjunction with dimensionless enthalpy variation. A sensitivity analysis against gas property variations is conducted to quantify the benefits gained in precision. Generally, the well-known relationships correlating the Mach number with total and static properties are based on the assumption of perfect gas and constant gas properties. Introducing dependency on temperature and/or chemical composition for the caloric properties of the semi-perfect gas, proper mean values are defined and some theoretical corrections are provided for the well-known equations. The mass flow compatibility equation is then based on the ‘corrected’ expression correlating dimensionless mass flow and Mach number and takes full account of gas property variations.
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Aircraft cost modelling using the genetic causal technique within a systems engineering approach
01/07/2007
R. Curran, S. Castagne, J. Early, M. Price, S. Raghunathan, J. Butterfield and A. Gibson
The paper is primarily concerned with the modelling of aircraft manufacturing cost. The aim is to establish an integrated life cycle balanced design process through a systems engineering approach to interdisciplinary analysis and control. The cost modelling is achieved using the genetic causal approach that enforces product family categorisation and the subsequent generation of causal relationships between deterministic cost components and their design source. This utilises causal parametric cost drivers and the definition of the physical architecture from the Work Breakdown Structure (WBS) to identify product families. The paper presents applications to the overall aircraft design with a particular focus on the fuselage as a subsystem of the aircraft, including fuselage panels and localised detail, as well as engine nacelles. The higher level application to aircraft requirements and functional analysis is investigated and verified relative to life cycle design issues for the relationship between acquisition cost and Direct Operational Cost (DOC), for a range of both metal and composite subsystems. Maintenance is considered in some detail as an important contributor to DOC and life cycle cost. The lower level application to aircraft physical architecture is investigated and verified for the WBS of an engine nacelle, including a sequential build stage investigation of the materials, fabrication and assembly costs. The studies are then extended by investigating the acquisition cost of aircraft fuselages, including the recurring unit cost and the non-recurring design cost of the airframe sub-system. The systems costing methodology is facilitated by the genetic causal cost modeling technique as the latter is highly generic, interdisciplinary, flexible, multilevel and recursive in nature, and can be applied at the various analysis levels required of systems engineering. Therefore, the main contribution of paper is a methodology for applying systems engineering costing, supported by the genetic causal cost modeling approach, whether at a requirements, functional or physical level.
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Performance characterisation of MPD thrusters
01/07/2007
T. R. Nada
This paper introduces a characterisation of the performance indices and operating limits of the self field magnetoplasmadynamic thruster. The thrust, specific impulse, and efficiency are considered as the main performance indices, while the operating limits are the cathode lifetime, onset phenomenon, and the overfed state of the thruster. The effects of thruster parameters (current, mass flow rate, geometry, and propellant type) on the performance indices and operating limits are examined using one-dimensional model of cylindrical self-field thrusters. Design charts are presented to help the designers to choose the optimum and safe set of the thruster parameters that realise certain mission requirements.
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Addressing pose estimation issues for machine vision based UAV autonomous serial refuelling
01/06/2007
G. Campa, M. R. Napolitano, M. Perhinschi, M. L. Fravolini, L. Pollini and M. Mammarella
This paper describes the results of an effort on the analysis of the performance of specific ‘pose estimation’ algorithms within a Machine Vision-based approach for the problem of aerial refuelling for unmanned aerial vehicles. The approach assumes the availability of a camera on the unmanned aircraft for acquiring images of the refuelling tanker; also, it assumes that a number of active or passive light sources – the ‘markers’ – are installed at specific known locations on the tanker. A sequence of machine vision algorithms on the on-board computer of the unmanned aircraft is tasked with the processing of the images of the tanker. Specifically, detection and labeling algorithms are used to detect and identify the markers and a ‘pose estimation’ algorithm is used to estimate the relative position and orientation between the two aircraft.
Detailed closed-loop simulation studies have been performed to compare the performance of two ‘pose estimation’ algorithms within a simulation environment that was specifically developed for the study of aerial refuelling problems. Special emphasis is placed on the analysis of the required computational effort as well as on the accuracy and the error propagation characteristics of the two methods. The general trade offs involved in the selection of the pose estimation algorithm are discussed. Finally, simulation results are presented and analysed.
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Investigation on the aerodynamic performance of an ejection seat
01/06/2007
1,2D. H. Chen, 1,2W. H. Wu, 1J. J. Wang and 2Y. Huang
A unique experimental method is used, in combination with numerical calculation and engineering estimation, to study the aerodynamic performance of an ejection seat at M = 0×60, 0×90 and 1×20, angles-of-attack a = 0°~360°, and sideslip angles b = 0°~–90°. Several basic characteristics of the aerodynamic performance are explored. The normal force of the ejection seat varies in a sinusoidal way and the axial force in a cosinoidal way, with the angle-of-attack. The model is statically unstable longitudinally at most attitude angles and the longitudinal stability could be improved by a stabiliser. These characteristics result from a large low pressure area caused by the leeward separation and the windward high pressure area in the ejection seat flow field, at all a, due to the blunt configuration. A set of engineering calculation formulae is deduced, based on the aerodynamic characteristics of the ejection seat.
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Three-dimensional indicial response of finite aspect ratio yawed wings
01/06/2007
C. E. Manglano-Villamarin and S. T. Shaw
The influence of finite aspect ratio and yaw on the computed indicial response of a pitching wing has been studied using numerical solutions of the unsteady Euler equations. The indicial response was obtained directly from computations of the unsteady flow around two- and three-dimensional wings subjected to a step change in incidence at Mach numbers between 0×2 and 0×7. The data reveal several important characteristics in the behaviour of the unsteady response of three-dimensional wings. The initial response is shown to be independent of both aspect ratio and yaw confirming the results of linearized theory. During the subsequent development of the unsteady response significant differences are observed between the two- and three-dimensional behaviours as a consequence of changes to both wing aspect ratio and yaw angle. The formation and spanwise propagation of acoustic waves due to finite aspect ratio is shown to have a significant influence on the development of the unsteady forces, while for yawed wings the results indicate that the manner in which the windward and leeward tip vortices form is important. Based upon these observations it is suggested that the current practice within the rotorcraft community in which two-dimensional indicial response functions are employed may be unreliable for the advancing blade.
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Use of Global Positioning System velocity outputs for determining airspeed measurement error
01/06/2007
G. B. Gratton
Several methods have been derived since the advent of GPS (Global Positioning System) receivers in aircraft cockpits by which these receivers may be used to calibrate these aircraft’s other instrumentation; in particular the pitot-static system. This paper presents the four most suitable methods, two of which have been developed by the author. These methods are shown with a common symbology, and their strengths, weaknesses, analysis and operational use are compared.
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A proposed reference framework for unmanned aerial vehicle and system airworthiness requirements
01/06/2007
A. Maneschijn, T. Jones, T. W. von Backström and L. A. Ingham
Various programmes are underway internationally to establish legislative instruments for regulating civil and military unmanned aerial vehicles and systems. An analysis of a selection of these programmes revealed that the approaches used for airworthiness regulation are not harmonised and are usually limited to specific unmanned aerial vehicle types, indicating the need for a generic framework for airworthiness requirements. A functional Reference Framework for unmanned aerial vehicle and system airworthiness requirements was developed using Annex 8 of the Chicago Convention as a reference basis, supplemented with airworthiness procedures and functional requirements derived from manned aircraft regulations, unmanned aerial vehicle and system airworthiness material, and flightworthiness guidelines for reusable launch vehicles. Various airworthiness elements were identified for which further research is required to develop appropriate airworthiness requirements. This paper summarises the development of the framework and proposes the Reference Framework as a functional basis for generating comprehensive South African civil and military airworthiness requirements for unmanned aerial vehicles and systems.
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Strategic destruction of the Western commercial aircraft sector: Implications of systems integration and international risk-sharing business models
01/05/2007
D. Pritchard and A. MacPherson
This paper offers a critical perspective on the changing organisational structure of the Western commercial aircraft industry. The role of systems integration based on risk-sharing partnerships for new aircraft programmes is explored. We find that build-to-print subcontracting relationships are being replaced by internationally devolved design and engineering tasks for airframe development, signaling a profound change in the geography of commercial aircraft production. While sensible from a financial standpoint, the international outsourcing of design-intensive production entails substantial amounts of technology transfer – including the delivery of proprietary knowledge to risk-sharing partners. For several of the advanced market economies, including Canada, France, Germany, the UK, and the US, the long-range strategic downside is that foreign risk-sharing partners could eventually become competitors. Systems integration on a risk-sharing basis also implies home-country job-losses among skilled workers with expertise in design, engineering, and R&D.
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Design of fixed wing micro air vehicles
01/05/2007
P. Cosyn and J. Vierendeels
The paper describes the methodology and computational design strategies used to develop a series of fixed wing micro air vehicles (MAVs) at the Ghent University. The emphasis of the research is to find an optimal MAV-platform that is bound to geometrical constraints but superior in its performance. This requires a multidisciplinary design optimisation but the challenges are mainly of aerodynamic nature. Key areas are endurance, stability, controllability, manoeuvrability and component integration. The highly three-dimensional low Reynolds number flow, the lack of experimental databases and analytical or empirical models of MAV-aerodynamics required fundamental research of the phenomena. This includes the use of a vortex lattice method, three-dimensional CFD-computations and a numerical propeller optimisation method to derive the forces and their derivatives of the MAV and propeller for performance and stability-related optimisation studies. The design method leads to a simple, stable and robust flying wing MAV-platform that has the agility of a fighter airplane. A prototype, the UGMAV25, was constructed and flight tests were performed. The capabilities of the MAV were tested in a series of successful flight manoeuvres. The UGMAV15, a MAV with a span of 15cm, is also developed to test flight-qualities and endurance at this small scale. With the current battery technology, a flight-time of at least one hour is expected.
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On different parameterisation methods to analyse spacecraft attitude manoeuvres in the presence of attitude constraints
01/05/2007
G. Radice and M. Casasco
This paper analyses and compares two different attitude representations, using quaternions and modified Rodrigues parameters, in the context of the potential function method applied to autonomously control constrained attitude slew manoeuvres. This method hinges on the definition of novel Lyapunov potential functions in terms of the attitude parameters representing the current attitude, the goal attitude and any pointing constraints, which may be present. It proves to be successful in forcing the satellite to achieve the desired attitude while at the same time avoiding the pointing constraints. A linearised version of the modified Rodrigues parameterisation is also introduced and analysed. Finally advantages and drawbacks of all attitude representations are discussed.
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A change in the calculated impact of supersonic aircraft NOx emissions on the atmosphere
01/05/2007
O. Dessens, H. L. Rogers and J. A. Pyle
New model calculations suggest that the potential impact on the atmosphere of a future fleet of supersonic aircraft, for the year 2015, is highly dependent upon the amount of nitrogen oxides (NOx) emitted from the fleet. This result contrasts with the IPCC assessment(1) which suggested that the impact of supersonic aircraft on the atmosphere was primarily through the role of water vapour emissions both on atmospheric ozone and climate change. These new findings are extremely important for atmospheric scientists, the aviation industry and policy makers, highlighting the importance of further development of low NOx combustors for supersonic aircraft, an aspect which has been largely ignored following the IPCC Special Report.
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Modelling and vibration of a non-classical tilt-rotor wing system
01/05/2007
O. Song, H. D. Kwon and L. Librescu
Problems related with the mathematical modelling and eigenvibration of a tiltrotor aircraft-wing system built up of anisotropic composite materials are investigated. The wing-mounted rotor that can tilt from the vertical position to a horizontal one is modelled and analysed from the vibrational point of view. In this sense, its behaviour is analysed as a function of the mass size, mass moment of inertia, tilt angle and spin speed of the spinning rotor and of its location along the wing span. While the rotor is considered to be rigid, the aircraft wing is modelled as a thin-walled beam that features a doubly-symmetric cross-section contour and incorporates the elastic coupling between flap-lag-transverse shear, on one hand, and between extension-twist, on the other hand. Numerical simulations are provided and pertinent conclusions are outlined.
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Methods for the design of energy efficient high speed aerospace vehicles
01/05/2007
D. Riggins, T. Taylor, L. Terhune and D. Moorhouse†
This paper continues development of the fundamental analytical science, methodology and tools required for the analysis, design, and optimisation of high speed aerospace vehicles in terms of the efficient use of on-board energy. Specifically, it presents the complete second-law characterisation and related system-level energy management effectiveness for high-speed vehicles (coupling both aerodynamic and propulsive subsystems). Modelling of the fluid dynamics utilises high-level (multi-dimensional) flow-fields representative of generic configurations of interest. Capability has been recently developed which allows detailed second-law performance audits in terms of the ‘common currency’ of entropy generation for high-speed vehicles (involving complete synthesis of both internal and external flow-fields, i.e. both aerodynamic and propulsive sub-systems). This capability is now extended to encompass and utilise multi-dimensional flow-fields generated by computational fluid dynamics solvers, including Navier-Stokes solvers. Furthermore, the methodology is shown in this paper to provide insight and fundamental direction for management of on-board energy (‘price paid’) for maximum performance missions.
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Modelling and vibration of a non-classical tilt-rotor wing system
01/05/2007
O. Song and H. D. Kwon and L. Librescu
Problems related with the mathematical modelling and eigenvibration of a tiltrotor aircraft-wing system built up of anisotropic composite materials are investigated. The wing-mounted rotor that can tilt from the vertical position to a horizontal one is modelled and analysed from the vibrational point of view. In this sense, its behaviour is analysed as a function of the mass size, mass moment of inertia, tilt angle and spin speed of the spinning rotor and of its location along the wing span. While the rotor is considered to be rigid, the aircraft wing is modelled as a thin-walled beam that features a doubly-symmetric cross-section contour and incorporates the elastic coupling between flap-lag-transverse shear, on one hand, and between extension-twist, on the other hand. Numerical simulations are provided and pertinent conclusions are outlined.
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Relationships between flying qualities and flight tests parameters for the F/A-18 aircraft
01/04/2007
R. M. Botez and M. Rotaru
In this Technical Note, is shown that relationships exist between flying qualities levels 1, 2 and 3 and flight conditions expressed in terms of Mach numbers, altitudes and angles-of-attack for the F/A-18 SRA (System Research Aircraft). These relationships are helpful in detecting if derivatives are well calculated for flight tests intermediate conditions.
The stability and control derivatives were calculated at NASA Dryden Flight Research Center DFRC laboratories for a number of 52 flight test conditions for the longitudinal and lateral aircraft motion. Flight tests were considered at Mach numbers between 0×3 and 1×3, at altitudes between 1,000ft and 40,000ft and at angles-of- attack vary between 1º and 10º. Following two methods were used to calculate the characteristic system eigenvalues: the approximate method and the exact method.
From these eigenvalues, by use of the classic vibration equation, the natural frequencies and damping were determined for the longitudinal and for the lateral aircraft motion(1). In case of the longitudinal aircraft motion, the flying qualities were evaluated for the long and short period of motion, while for the lateral aircraft motion, the flying qualities were evaluated for the roll, Dutch roll and spiral motions. In the following paragraphs, results are presented.
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A systems approach to training aeronautical decision making: from identifying training needs to verifying training solutions
01/04/2007
W.-C. Li and D. Harris
The human factors analysis and classification system (HFACS) was developed as an analytical framework for the investigation of the role of human error in aviation accidents. A total of 523 accidents in the Republic of China (ROC) Air Force between 1978 and 2002 were analysed using this framework. The results showed that in a great many cases, poor pilot decision making was implicated. Following a survey of flight instructors’ opinions, two of most promising mnemonic-based methods currently available to guide the decision making of pilots were identified (SHOR and DESIDE). These methods were developed into a short (four hour) aeronautical decision making training course. A total of 41 pilots from the Republic of China Tactical Training Wing then participated in a study to evaluate the effectiveness of this training course. Half of the participants received the short ADM training programme and half did not. Their decision making skill was evaluated in a series of emergency situations presented in a full-flight simulator. Furthermore, their decision making processes were examined in a series of pencil-and-paper based tests. The results clearly showed significant improvements in the quality of pilots’ situation assessment and risk management (underpinning processes in pilot decision making) although this was usually at the expense of speed of response. Pilots used the quicker to apply SHOR mnemonic in situations that which required a fast decision and the more comprehensive but slower to perform DESIDE method when there were fewer time pressures. The results do strongly suggest that ADM is trainable and the short programme devised was effective.
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Development of extended ultra high lift low pressure turbine blades using selective roughness and wake unsteadiness
01/04/2007
R Howell and K M Roman
This paper describes how it is possible to reduce the profile losses on ultra high lift low pressure (LP) turbine blade profiles with the application of selected surface roughness and wake unsteadiness. Over the past several years, an understanding of wake interactions with the suction surface boundary layer on LP turbines has allowed the design of blades with ever increasing levels of lift. Under steady flow conditions, ultra high lift profiles would have large (and possibly open) separation bubbles present on the suction side which result from the very high diffusion levels. The separation bubble losses produced by it are reduced when unsteady wake flows are present. However, LP turbine blades have now reached a level of loading and diffusion where profile losses can no longer be controlled by wake unsteadiness alone.
The ultra high lift profiles investigated here were created by attaching a flap to the trailing edge of another blade in a linear cascade — the so called flap-test technique. The experimental set-up used in this investigation allows for the simulation of upstream wakes by using a moving bar system. Hotwire and hotfilm measurements were used to obtain information about the boundary-layer state on the suction surface of the blade as it evolved in time. Measurements were taken at a Reynolds numbers ranging between 100,000 and 210,000.
Two types of ultra high lift profile were investigated; ultra high lift and extended ultra high lift, where the latter has 25% greater back surface diffusion as well as a 12% increase in lift compared to the former. Results revealed that distributed roughness reduced the size of the separation bubble with steady flow. When wakes were present, the distributed roughness amplified disturbances in the boundary layer allowing for more rapid wake induced transition to take place, which tended to eliminate the separation bubble under the wake. The extended ultra high lift profile generated only slightly higher losses than the original ultra high lift profile, but more importantly it generated 12% greater lift.
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Development of a parametric-based indirect aircraft structural usage monitoring system using artificial neural networks
01/04/2007
S C Reed
The development of a parametric-based indirect aircraft structural usage monitoring system using artificial neural networks is described. Flight parametric data, captured during Operational Loads Measurement have been used to predict strains or stresses at key structural locations for several military aircraft types, using mapping relationships determined by artificial neural networks. A framework for the development of a neural network-based structural usage monitor is discussed and the basic architecture of the multilayer perceptron artificial neural network is described. Additionally, results from case studies are presented. It is concluded that this technology could provide the basis for accurate, cost-effective structural usage monitoring systems across the range of military aircraft types and roles.
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The Mil-Std-1553B data bus: What does the Future hold?
01/04/2007
D R Bracknell
Numerous military platforms (land, sea and air) feature serial data bus technology based on the US MIL-STD-1553B data bus standard for integration of their digital systems. Many of these platforms have 15-20 years of operational life remaining, but the installed 1553B data buses (data networks) having only a 1Mbit/sec transfer rate are unable to meet many of the future data networking requirements. Research into new, higher performance data networks has concentrated on modern alternatives with throughput increases of two to three orders of magnitude (100Mbit/sec to 1Gbit/sec). These are generally based on modern commercial-off-the-shelf (COTS) standards, good examples being Ethernet and Fibre Channel. Some are already being employed in military platforms having been ruggedised for the harsh physical and electro-magnetic environment. However these COTS systems while being a natural choice for new platforms may not be cost effective for upgrading older platforms. This paper plots the history of MIL-STD-1553, possibly the most successful military platform standard of all time, and discusses some of the options for increasing its performance and economically extending its life into the future.
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Analysis of composite plates with variable stiffness using Galerkin method
01/04/2007
E Sencocak and H Tanriover
A solution methodology is developed to solve plane stress problem of composite plates with variable stiffness by using Galerkin technique and polynomials as trial functions. In the solution process, analytical computation has been done wherever it is possible, and analytical-numerical type approach has been made for all problems. The methodology is applied to two known case problems, composite plate with variable fibre content and laminated plate with spatially varying fibre orientations. The formulation of these problems results into coupled partial differential equations (with variable coefficients). The solutions of these equations are obtained using the polynomials as trial functions in the Galerkin method. The results are compared to that of Ritz and collocation technique published elsewhere. The method is found to determine closely both the displacements and the stresses with a few number of terms and in good agreement with other approximating methods. Computations on some examples show that, the method with the help of a symbolic math package is simple and efficient for solving these types of problems in engineering applications.
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Application of a parallel rotor CFD code on HPCx
01/03/2007
C. B. Allen, A. G. Sunderland and R. Johnstone
Aspects of parallel simulation of rotor flows are considered. These flows can be extremely expensive for a compressible finite-volume CFD code, and parallelisation can be essential. The award of HPCx time through the UK Applied Aerodynamics Consortium has allowed large rotor simulations to be performed and wake grid dependence to be investigated. However, there are several issues that need to be investigated when considering very large simulations, including the grid generation process, the parallel flow-solver, including an effective mesh motion approach, and visualisation options. Details of these are presented here, with particular emphasis on the flow-solver parallel performance. A detailed performance analysis of the unsteady flow-solver has been undertaken and the code optimised to improve parallel performance, and details of the parallel scaling performance are presented. The parallel scaling of the code is very good on all the HPC architectures tested here, and this has been recognised by an HPCx Gold Star Capability Incentive award. Results of simulation of a four-bladed lifting rotor in forward flight are also presented, for two mesh densities. It is shown that the solution computed on the serial limit on mesh size, around four million cells, exhibits excessive diffusion, and is of limited use in terms of detailed flow features. The results on a very fine mesh, 32 million cells, have shown a much better solution resolution, and it is also demonstrated that the l2 vortex core visualisation option is extremely useful.
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High performance computing and computational aerodynamics in the UK
01/03/2007
D. R. Emerson, A. J. Sunderland, M. Ashworth and K. J. Badcock
The establishment of the UK Applied Aerodynamics Consortium in 2004 brought together many of the UK’s leading research groups to tackle challenging aerodynamic problems on the national computing facility, HPCx. This paper provides a brief history of some early pioneers of numerical simulation and highlights some key contributions to development in parallel processing that laid the foundations for today’s researchers. The transition from vector to massively parallel processing is discussed from a UK viewpoint along with technological barriers that could have a significant impact on future systems. Solutions to these barriers are already being sought and the paper discussed some of the novel technologies that may be deployed in the future. In its short history, the consortium has made substantial progress and this is briefly discussed with several highlights that illustrate the scientific output. Although a number of challenges are identified, particularly with respect to developing a comprehensive visualisation capability, the consortium is well placed to build upon its initial success.
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Large-eddy simulation of twin impinging jets in cross-flow
01/03/2007
Q. Li, G. J. Page and J. J. McGuirk
The flow-field beneath a jet-borne vertical landing aircraft is highly complex and unsteady. large-eddy simulation is a suitable tool to predict both the mean flow and unsteady fluctuations. This work aims to evaluate the suitability of LES by applying it to two multiple jet impingement problems: the first is a simple twin impinging jet in cross-flow, while the second includes a circular intake. The numerical method uses a compressible solver on a mixed element unstructured mesh. The smoothing terms in the spatial flux are kept small by the use of a monitor function sensitive to vorticity and divergence. The WALE subgrid scale model is utilised. The simpler jet impingement case shows good agreement with experiment for mean velocity and normal stresses. Analysis of time histories in the jet shear layer and near impingement gives a dominant frequency at a Strouhal number of 0×1, somewhat lower than normally observed in free jets. The jet impingement case with an intake also gives good agreement with experimental velocity measurements, although the expansion of the grid ahead of the jets does reduce the accuracy in this region. Turbulent eddies are observed entering the intake with significant swirl. This is in qualitative agreement with experimental visualisation. The results show that LES could be a suitable tool when applied to multiple jet impingement with realistic aircraft geometry.
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Achieving high parallel performance for an unstructured unsteady turbomachinery CFD code
01/03/2007
N. Hills
This paper describes the work done to achieve high parallel performance for an unstructured, unsteady turbomachinery computational fluid dynamics (CFD) code. The aim of the work described here is to be able to scale problems to the thousands of processors that current and future machine architectures will provide. The CFD code is in design use in industry and is also used as a research tool at a number of universities. High parallel scalability has been achieved for a range of turbomachinery test cases, from steady-state hexahedral mesh cases to fully unsteady unstructured mesh cases. This has been achieved by a combination of code modification and consideration of the parallel partitioning strategy and resulting load balancing. A sliding plane option is necessary to run fully unsteady multistage turbomachinery test cases and this has been implemented within the CFD code. Sample CFD calculations of a full turbine including parts of the internal air system are presented.
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Prediction of aerodynamic forces on a helicopter fuselage
01/03/2007
A. Filippone
This paper presents a critical analysis of the aerodynamic loads created by the airframe of a conventional helicopter. The airframe is modelled and computed with an implicit, multi-block, multi-grid parallel Navier-Stokes solver. The flow solver has been optimised and run on up to 200 parallel processors. The cases reported include the effects of angle-of-attack (positive and negative), the effects of yaw (starboard and port) and side flow. Finally, the effects of the support strut in the wind tunnel experiments have been evaluated. Data are shown for the lift, drag and side force coefficients at flight Reynolds numbers (Re = 30m). A case of 30 degrees yaw at a flight Reynolds number is shown. We conclude that with the use of top-end computer resources it is possible to calculate the aerodynamic coefficients with a good degree of accuracy if the flow is mostly attached.
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Parallel adjoint-based optimisation of a blended wing body aircraft with shock control bumps
01/03/2007
W. S. Wong, A. Le moigne and N. Qin
An Euler optimisation for a BWB configuration with winglets incorporating an array of three-dimensional shock control bumps is carried out by employing an efficient adjoint-based optimisation methodology. A high fidelity multi-block grid with over two million grid points is generated to resolve the shape of the 3D shock control bumps, the winglet as well as the overall BWB shape, which are parameterised by over 650 design variables. In order to perform such a large aerodynamic optimisation problem feasibly, the optimisation tools such as the flow solver and the adjoint solver have to be parallelised with a good parallel efficiency. This paper reports the parallel implementation efforts on the adjoint solver; especially on the calculation of the sensitivity derivatives, which has to be looped over the total number of design variables. Results from the optimisation of the wing master sections, winglet aerofoil sections and the three dimensional bumps indicate a significant improvement regarding the aerodynamic performance against the baseline geometry for the given planform layout of the aircraft.
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Numerical study of transonic covity flows usinf large-eddy and detached-eddy simulation
01/03/2007
P. Nayyer, G. N. Barakos and K. J. Badcock
Numerical analysis of the flow in weapon bays modelled as open rectangular cavities of length-to-depth (L/D) ratio of 5 and width-to-depth (W/D) ratio of 1 with doors-on and doors-off is presented. Flow conditions correspond to Mach and Reynolds numbers (based on cavity length) of 0×85 and 6×783m respectively. Results from unsteady Reynolds-averaged Navier-Stokes (URANS), large-eddy simulation (LES) and detached-eddy simulation (DES) are compared with the simulation methods demonstrating the best prediction of this complex flow. It was found that URANS was not able to predict the change of flow characteristics between the doors-on and doors-off configurations. In addition, the energy content of the cavity flow modes was much better resolved with DES and LES. Further, the DES was found to be quite capable for this problem giving accurate results (within 3dB of) experiments and appears to be a promising alternative to LES for modelling massively separated flows.
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An unsteady, moving mesh CFD simulation for Harrier hot-gas ingestion control analysis
01/03/2007
G. A. Richardson, W. N. Dawes and A. M. Savill
Hot gas ingestion (HGI) can be a problematic feature of short take-off vertical landing (STOVL) aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows.
A flow solver has been developed to include a suitable linear mesh deformation technique for the descending aircraft configuration. The code has been applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. This has enabled an understanding of the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake.
This paper presents three sets of CFD results. First a validation exercise shows predicted results from the twin-jet with intake in cross-flow test-case. This is an unsteady Reynolds averaged Navier Stokes (URANS) solution for a static geometry (there is no moving mesh). This allows comparison with experiment. Secondly, a full descent phase URANS Spalart-Allmaras (SA) turbulence model calculation is done on an 8×5m cell mesh for half the flow domain of the Harrier model and test-rig without dams/strakes. This shows how the HGI flow mechanisms affect the engine intake temperature profiles, for the case where there are no flow control methods on the underside of the aircraft. Thirdly, the full descent phase URANS SA turbulence model calculation is done on a 22×4m cell mesh for the full flow domain of the Harrier model and test-rig, with the dam/strake geometry included in the structured mesh region.
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Design and performance of thin, circular arc, wind-tunnel turning vanes
01/02/2007
G. Johl, M. Passmore and P. Render
Although test rig data exists for ¼ circle turning vanes, the actual performance of these vanes once installed in a wind tunnel, and the extent to which test rig results are replicated, is rarely known. This paper compares pressure loss coefficient and velocity profile data from a vane test module with measurements taken in the low speed wind tunnel described in Ref. 1. The pressure loss coefficient, KL is defined as the ratio between the static pressure loss in a corner and the inlet dynamic pressure. Previous investigations in test rigs have shown that thin ¼ circle turning vanes with a space to chord ratio (s/c) of between 0×20-0×25, produced 0×12 < KL < 0×20(2)(3)(4)(5). However, these sources focused on determining KL rather than quantifying the flow quality downstream of the vanes. Although KL, is important in terms of achieving a high tunnel energy ratio, it is perhaps secondary to downstream flow quality since the stream exiting the corners of a typical wind tunnel enter into components whose performance may be affected by flow quality.
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Lean engineering: a framework for doing the right thing right
01/02/2007
H. L. McManus, A. Haggerty and E. Murman
Lean techniques are having a major impact on aerospace manufacturing. However, the cost and value of aerospace (and many other) products is determined primarily in product development. Migrating lean to engineering processes is ongoing in the industry, and a subject of study at the MIT Lean Aerospace Initiative. This paper summarises findings to date, with references to both research literature and successful implementation examples. To implement lean engineering, a three-part approach is needed: Creating the right products, with effective lifecycle and enterprise integration, using efficient engineering processes.
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Performance of non-rigid airships operating in the neutral buoyancy condition
01/02/2007
G. E. Dorrington
The feasibility of using neutrally-buoyant (or fully-buoyant) airships
for passenger and cargo transportation is investigated. The drag
coefficients of rigid and non-rigid airships are deduced from flight
data. Comparisons are made with empirical drag formulas and
previous wind tunnel data. Some general trends for airship drag are
derived. The mass breakdown of non-rigid airships with hull
volumes up to 35,000m3 is analysed using parametric equations. The
maximum feasible airspeed and useful load carrying capacity of
projected airships are calculated. ‘Specific productivity’ is found to
be lower than values achievable with fixed-wing aircraft, but ‘fuelspecific
productivity’ is found to be competitive, confirming results
of a previous NASA study. The use of gaseous hydrogen and fuel
cells is briefly discussed.
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Rotorcraft simulation modelling and validation for control law design
01/02/2007
B. J. Manimala, D. J. Walker, G. D. Padfield, M. Voskuijl and A. W. Gubbels
This paper describes the development and validation of a high fidelity simulation model of the Bell 412 helicopter for handling qualities and flight control investigations. The base-line model features a rigid, articulated blade-element formulation of the main rotor, with flap and lag degrees of freedom. The Bell 412 HP engine/governor dynamics are represented by a second-order system. Other key features of the base–line model include a finite-state dynamic inflow model and lag damper dynamics. The base-line model gives excellent agreement with flight-test data over the speed range 15-120kt for on-axis responses. Prediction of off-axis responses is less accurate. Several model enhancement options were introduced to obtain an improved off-axis response. It is shown that the pitch/roll off-axis responses in transient manoeuvres can be improved significantly by including wake geometry distortion effects in the Peters-He finite-state dynamic inflow model.
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New commercial opportunities in space
01/02/2007
D. M. Ashford
This paper assesses new commercial opportunities in space. The
main conclusion is that spaceplanes can reduce the cost of human
transport to orbit sufficiently for large new commercial markets to
develop. Combining the reusability of spaceplanes with the high
traffic levels of space tourism offers the prospect of a thousandfold
reduction in the cost per seat to orbit. The result will be airline
operations to orbit involving dozens of spaceplanes, each capable of
one or two flights per day. These low costs will make possible a
rapid expansion of space science and exploration.
The prototype of a small orbital spaceplane, needed to trigger this
line of development, could be developed in about six years at a cost
comparable to one or two flights of the Space Shuttle. It might be
possible to progress from this prototype to airline operations within
ten years, given a massive development effort.
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Numerical exploration of starting process in supersonic nozzle
01/01/2007
S. Saha and D. Chakraborty
The starting process in a supersonic nozzle is numerically simulated. The Navier Stokes equations, in axisymmetric form, are solved using a higher order spatial and temporal accurate scheme. Good comparisons between experimental and numerical values of various flow parameters form the basis of further analysis. The insight of the starting process in the nozzle, namely, the movement of primary and secondary shocks and contact discontinuity, has been obtained through analysis of various flow parameters. It has been observed that the inviscid phenomenon is more predominant in the flow development process. Parametric studies have been carried out to determine the effect of nozzle divergence angle on the starting process.
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Aircraft flight characteristics in conditions of windshear and icing
01/01/2007
Yihua Cao and Kungang Yuan
Complex weather conditions, especially windshear and icing
encounter, have severe effects on aircraft flight safety. The effect of
low-altitude windshear and ice accretion on aircraft performance and
control has been studied in this paper. With the employment of a
windshear model and nonlinear inverse dynamics (NID) method, a
low-altitude windshear penetration flight control law is designed.
The effect of ice accretion was modeled on the stability and control
of an aircraft. Several icing parameters are imported to the small
disturbance flight dynamics model to calculate the change of performance,
stability and control derivatives between clean and iced
aircraft. These derivatives were used to calculate the elevator, the
aileron and the rudder step responses to investigate the icing effect.
The simulation results indicate that the NID control logic works
effectively in the trajectory control of the aircraft during the
penetration of windshear. The method used to study the effect of ice
accretion on aircraft is valid and it can provide data for real-time
calculation for icing encounter.
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Effect of stagnation temperature on supersonic flow parameters applicatio for air in nozzles
01/01/2007
T. Zebbiche and Z. Youbi
When the stagnation temperature of a perfect gas increases, the specific heats and their ratio do not remain constant and start to vary with the temperature. The gas remains perfect; its state equations remain valid, so it can be named as calorifically imperfect gas. The aim of this research is to develop the necessary thermodynamic and geometrical equations and to study the supersonic flow at high temperature, lower than the dissociation threshold. The results are found by the resolution of nonlinear algebraic equations and integration of complex analytical functions where the exact calculation is impossible. The dichotomy method is used to solve the nonlinear equations and Simpson’s algorithm for the numerical integration applied. A condensation of the nodes is used. The functions to be integrated have a high gradient at the extremity of the interval of integration. The comparison is made with the calorifically perfect gas to determine the error. The application is made for air in a supersonic nozzle.
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Computation and experimental investigations for low-Reynolds number flows past and aerofoil
01/01/2007
W. Yuan, M. Khalid, J. Windte, U. Scholz and R. Radespiel
This paper presents investigations of low-Reynolds-number flows past an SD7003 airfoil at Re = 60k, where transition takes place across a laminar separation bubble (LSB). Results of experimental measurements and numerical calculations are analyzed and discussed. In particular, reasonably good results were obtained using two different numerical approaches: Large-eddy simulation (LES) that demonstrated vortical structures at different transition stages, and where the transition occurred naturally; unsteady Reynolds-averaged Navier-Stokes (URANS) simulations for several turbulence models based on the w-length-scale equation, coupled to a linear stability solver to predict the transition position.
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Optical imaging techniques for hypersonic impulse facilities
01/01/2007
T. J. McIntyre, H. Kleine and A. F. P. Houwing
The application of optical imaging techniques to hypersonic facilities is discussed and examples of experimental measurements are provided. Traditional schlieren and shadowgraph techniques still remain as inexpensive and easy to use flow visualisation techniques. With the advent of faster cameras, these methods are becoming increasingly important for time-resolved high-speed imaging. Interferometry’s quantitative nature is regularly used to obtain density information about hypersonic flows. Recent developments have seen an extension of the types of flows that can be imaged and the measurement of other flow parameters such as ionisation level. Planar laser induced fluorescence has been used to visualise complex flows and to measure such quantities as temperature and velocity. Future directions for optical imaging are discussed.
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Waypoint navigation for a micro air vehicle using vision-based attitude estimation
01/12/2006
J. J. Kehoe, R. S. Causey, M. Abdulrahim and R. Lind
Missions envisioned for micro air vehicles may require a high degree of autonomy to operate in unknown environments. As such, vision is a critical technology for mission capability. This paper discusses an autopilot that uses vision coupled with GPS and altitude sensors for waypoint navigation. The vision processing analyses a horizon to estimate roll and pitch information. The GPS and altitude sensors then command values to roll and pitch for navigation between waypoints. A flight test of a MAV using this autopilot demonstrates the resulting closed-loop system is able to autonomously reach several waypoints. The vehicle actually uses a telemetry link to a ground station on which all vision processing and related guidance and control is performed. Several issues, such as estimating heading to account for slow updates, are investigated to increase performance.
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Considerations for flight testing of UAVs in South African airspace
01/12/2006
L. A. Ingham, T. Jones and A. Maneschijn
South Africa has strategic requirements for tasks such as maritime patrol and border control. Research on UAVs should be done in order to design, certify and operate UAVs in civil airspace to satisfy these requirements. If principles such as equivalence, initially proposed by Eurocontrol are to be adopted in South Africa, it then follows that similar standards used by manned aircraft should be used by UAVs. Similarly, because the process of creating UAV regulations has not kept up with the pace of UAV development, and because dedicated UAV regulations do not yet exist in South Africa, UAVs must be tested and evaluated in order to prove compliance with comparable manned aircraft regulations in the foreseeable future until regulations are created or modified to accommodate UAVs. Given the airspace restrictions, and lack of applicable standards and regulations, proper flight testing of UAVs can become a very specialized task. Most test techniques applied to testing of manned aircraft are fortunately equally applicable to UAVs. This is a research-based paper that provides guidance to flight testers, UAV developers and research organizations wishing to execute tests in South Africa by suggesting a number of considerations for testing of UAVs.
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Aeroelastic response of helicopter rotors using a 3D unsteady aerodynamic solver
01/12/2006
M. Gennaretti and G. Bernardini
The prediction of blade deflections and vibratory hub loads concerning helicopter main rotors in forward flight is the objective of this work. They are determined by using an aeroelastic model derived through the coupling between a nonlinear blade structural model and a boundary integral equation solver for three-dimensional, unsteady, potential aerodynamics. The Galerkin method is used for the spatial integration, whereas the periodic blade response is determined by a harmonic balance approach. This aeroelastic model yields a unified approach for aeroelastic response and blade pressure prediction that may be used for aeroacoustic purposes, with the possibility of including effects from both blade-vortex interaction and multiple-body aerodynamic interaction. Quasi-steady aerodynamic models with wake-inflow from the three-dimensional aerodynamic solver are also applied, in order to perform a comparative study. Numerical results show the capability of the aeroelastic tool to evaluate blade response and vibratory hub loads for a helicopter main rotor in level flight conditions, and examine the sensitivity of the predictions on the aerodynamics model used.
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Decoupled controller for mixed exhausts turbofan engine
01/12/2006
T. R. Nada
This paper points out the capabilities of fully decoupled fuzzy controller which introduces simple design approach to deal with the coupling effects in controlling two spools, mixed exhausts turbofan engines. The decoupling is performed through proper selection of input parameters to the controller. Digital nonlinear engine/control system simulation is used to construct the fuzzy rules depending on simple logic. The performance of this controller is compared with that of an optimal controller representing efficient classical and conventional techniques. The decoupled fuzzy control system produces favorable transient strategies that other conventional controllers can not attempt due to its inherent proportionality characteristics. It displays improvements in surge margin for both fan and compressor, and temperature margin with almost similar response time during acceleration. Also, the proposed controller has the capabilities to increase the response speed during deceleration independently from acceleration transient.
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Using system engineering on an aircraft improvement project
01/12/2006
J. C. Hsu
A complete system engineering process is applied to a pilot project that will determine the initial deployment of the system engineering process for future projects. It was a challenge to complete the entire systems engineering process to include project team utilization of system engineering tools in such a short time span. Therefore, systems engineering products had to be useful and productive to the project. The system requirements definition, Quality Function Deployment (QFD) evaluation, trade study, risk identification and risk mitigation processes were completed in a timely manner and assisted in the System Requirements, System Design and Preliminary Design Reviews successfully.
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3D numerical simulation of the supersonic combustion of H2
01/12/2006
Prashant Dinde, A. Rajasekaren and V. Babu
Results from numerical simulations of supersonic combustion of H2 are presented. The combustor has a single stage fuel injection parallel to the main flow from the base of a wedge. The simulations have been performed using FLUENT. Realisable k-e model has been used for modelling turbulence and single step finite rate chemistry has been used for modelling the H2-Air kinetics. All the numerical solutions have been obtained on grids with average value for wall y+ less than 40. Numerically predicted profiles of static pressure, axial velocity, turbulent kinetic energy and static temperature for both non-reacting as well as reacting flows are compared with the experimental data. The RANS calculations are able to predict the mean and fluctuating quantities reasonably well in most regions of the flow field. However, the single step kinetics predicts heat release much more rapid than what was seen in the experiments. Nonetheless, the overall pressure rise in the combustor due to combustion is predicted well. Also, the k-e model is not able to predict the fluctuating quantities in the base region of the wedge where there is strong anisotropy in the presence of combustion.
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A turbulence criterion for safe helicopter operations to offshore installations
01/11/2006
S. J. Rowe, D. Howson and G. Turner
This paper describes the development of a wind turbulence criterion for the safe operation of helicopters to offshore installations. The development of the criterion was recommended following a review of the environmental effects around offshore platform helidecks.
Currently, criteria exist for ambient temperature and for vertical wind component in the vicinity of helidecks, but a questionnaire-based survey of helicopter pilots revealed that the principal safety hazard and source of highest workload is turbulence around offshore installations. The new turbulence criterion will plug a long-standing gap in the guidance on offshore helideck design.
The paper describes how the criterion has been developed using piloted flight simulation in a research flight simulator together with data from wind tunnel tests on offshore platforms. Initial validation has been successfully performed, and extended to include correlation with the large database of helicopter operational flight data records being collected through the UK North Sea Helicopter Operations Monitoring Programme (HOMP).
The turbulence criterion will be used, together with existing criteria on vertical wind component and temperature, in the assessment of new offshore installation designs, or proposed modifications to existing designs, to determine wind conditions where turbulence is likely to be excessive for safe helicopter operations. These will be used to estimate helideck operability and thereby inform the installation topsides design process, and will provide input to the setting and maintenance of helicopter operational limitations for individual installations.
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Pressure sensitive paint measurements on a delta-wing in supersonic flow
01/11/2006
L. C. Raju, L. Venkatakrishnan and P. R. Viswanath
Experiments have been performed documenting the pressure field on the lee-side of a delta-wing at three incidence angles (5°, 10°, and 15°) and at Mach 1•8 using a PSP (Pressure Sensitive Paint) technique. The delta-wing model having a leading edge sweep of 60° was instrumented with 31 spanwise pressure ports at 68% of mean chord location. The Optrod-B1 binary paint was utilised and the PSP images were processed employing a resection based methodology. The comparisons of PSP results with those measured employing pressure taps show good agreement at different incidence angles.
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Integration of friction stir welding into a multidisciplinary aerospace design framework
01/11/2006
A. H. van der Laan, R. Curran, M. J. L. van Tooren and C. Ritchie
Multidisciplinary design and innovative highly automated manufacturing methods are increasingly important to today’s aircraft industry: multidisciplinary design because it reduces lead-time and results in a better design, and automated manufacturing methods because they are more capable and reduce manufacturing cost. In this paper a cost estimation model is presented that integrates the manufacturing cost of friction stir welded connections within a multidisciplinary design decision tool. Due to the fact that friction stir welding is a new manufacturing method, the cost estimation model is based on the actual process physics, meaning what the process looks like in terms of processing speeds and characteristics. As an integral part of a multidisciplinary design framework, the developed cost estimation model contributes to a design support tool that assesses not only manufacturing but also structural and aerodynamic issues. It is shown that the cost model developed can be integrated into this more holistic design process support architecture. The predicted costs are accurate to the historical data and allow tradeoff of manufacturing and economic considerations within the context of the multidisciplinary design tool. The tradeoff capability is highlighted through a presented case study that compares the friction stir welding process as an alternative solution to more tradition riveting. Most importantly, this results in a quantitative tradeoff between two processes that shows the manufacturing cycle time of friction stir welding to be reduced by 60% and the recurring assembly cost by 20%.
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Further analysis of self-induced roll oscillations of a non-slender delta wing
01/11/2006
M. E. Beyers and L. E. Ericsson
In low-speed wind tunnel tests at alphaƒn= 25 and 30 deg of a 45 deg delta wing with semicircular leading edges limit cycle oscillations occurred around the 50 deg roll trim angle. In some cases the oscillations were highly regular, in other cases, highly irregular. An analysis of the observed roll-oscillation dynamics has shown that several viscous flow phenomena are involved, which depend strongly on the leading-edge geometry, and whose relative importance can vary dramatically with the existing Reynolds number in critical flow regions. The possible role of surface roughness in modifying the viscous flow/motion coupling to cause these dramatically different test results is examined.
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Research initiatives for improving the safety of offshore helicopter operations
01/11/2006
D. A. Howson
Since the late 1980’s, the UK Civil Aviation Authority (CAA) has been leading a programme of research aimed at improving the safety of offshore helicopter operations. The motivation for this initiative came from a major joint CAA/Industry review of helicopter airworthiness, commissioned in 1982. This study led to a number of research projects and other reviews which, in turn, led to further research projects. A total of over 20 projects have been undertaken covering airworthiness and operational issues, and covering helicopters and helidecks. This programme of work has been jointly funded and monitored by the UK CAA-run Helicopter Safety Research Management Committee (HSRMC). This paper provides a top-level summary of current activities on the seven main ‘live’ research projects
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Operations and aircraft design towards greener civil aviation using air-to-air refuelling
01/11/2006
R. K. Nangia
As civil aviation expands, environmental aspects and fuel savings are becoming increasingly important. Amongst technologies proposed for more efficient flight, air-to-air refuelling (AAR), ‘hopping’ and flying in close formation (drag reduction), all have significant possibilities. It will be interesting to know also how these technologies may co-exist e.g. AAR and formation flying. In military use, AAR is virtually indispensable. Its benefits are real and largely proven in hostile and demanding scenarios. We present a case for applying AAR in a civil context to show that substantial reductions in fuel burn for long-range missions are achievable. Overall savings, including the fuel used during the tanker missions, would be of the order of 30-40% fuel and 35-40% financial. These are very significant in terms of the impact on aviation’s contribution to reducing atmospheric pollution. AAR allows smaller, efficient (greener) aircraft optimised for about 3,000nm range to fulfil long-range route requirements. This implies greater usage of smaller airports, relieving congestion and ATC demands on Hub airports. Problems due to shed vortices and wakes at airports are reduced. Smaller engines will be needed. Integrated (accepted) AAR could lead to further benefits. Aircraft could take-off ‘light’, with minimum fuel and reserves and a planned AAR a few minutes into the flight. The ‘light’ aircraft would not require over-rating of the engines during take-off and would therefore be less noisy during take-off and climb-out, permitting more acceptable night operations.
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A method for predicting the rate and effect of approach to the stall of a microlight aeroplace
01/10/2006
G. B. Gratton
The stall and immediately post-stall behaviour of a microlight aeroplane are shown to be a function of the deceleration rate prior to the stall; therefore, it is necessary to use a representative deceleration rate when determining the acceptability of stall and post-stall handling qualities. This research has found means by which the range of deceleration rates likely to be seen in a particular type can be estimated, so that flight test programmes can ensure these rates are included, and thus aircraft are confirmed to have acceptable stalling characteristics. Recommendations are made towards the use of this research for all aircraft type, and of further work which might usefully be carried out.
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Wing tip vortex control using synthetic jets
01/10/2006
P. Margaris and I. Gursal
An experimental investigation was conducted to study the effect of synthetic jet (oscillatory, zero net mass flow jet) blowing near the wing tip, as a means of diffusing the trailing vortex. Velocity measurements were taken, using a Particle Image Velocimetry system, around the tip and in the near wake of a rectangular wing, which was equipped with several blowing slots. The effect of the synthetic jet was compared to that of a continuous jet blowing from the same configurations. The results show that the use of synthetic jet blowing is generally beneficial in diffusing the trailing vortex and comparable to the use of continuous jet. The effect was more pronounced for the highest blowing coefficient used. The driving frequency of the jet did not generally prove to be a significant parameter. Finally, the instantaneous and the phase-locked velocity measurements helped explain the different mechanisms employed by the continuous and synthetic jets in diffusing the trailing vortex.
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Single and multi-objective UAV aerofoil optimisation via hierarchical asynchronous parallel evolutionary algorithm
01/10/2006
L. F. Gonzalez, D. S. Lee, K. Srinivas and K. C. Wong
Unmanned aerial vehicle (UAV) design tends to focus on sensors, payload and navigation systems, as these are the most expensive components. One area that is often overlooked in UAV design is airframe and aerodynamic shape optimisation. As for manned aircraft, optimisation is important in order to extend the operational envelope and efficiency of these vehicles. A traditional approach to optimisation is to use gradient-based techniques. These techniques are effective when applied to specific problems and within a specified range. These methods are efficient for finding optimal global solutions if the objective functions and constraints are differentiable. If a broader application of the optimiser is desired, or when the complexity of the problem arises because it is multi-modal, involves approximation, is non-differentiable, or involves multiple objectives and physics, as it is often the case in aerodynamic optimisation, more robust and alternative numerical tools are required. Emerging techniques such as evolutionary algorithms (EAs) have been shown to be robust as they require no derivatives or gradients of the objective function, have the capability of finding globally optimum solutions among many local optima, are easily executed in parallel, and can be adapted to arbitrary solver codes without major modifications. In this paper, the formulation and application of a evolutionary technique for aerofoil shape optimisation is described.
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A comparative study of two UCAV type wing planforms - performance and stability considerations
01/10/2006
R. K. Nangia and M. E. Palmer
Currently there is a revival of interest in flying wings for military (and civil) use. The military context has arisen from the future ‘stealthy’ high altitude long endurance (HALE) and unmanned combat air vehicles (UCAV) aircraft. Questions on aerodynamics, control and structural efficiency arise. Compared with conventional wing/tail arrangements, flying wings have a special set of very different constraints. These are mentioned. Without a trim surface, the constraints on the wing pitching moment dictate the design camber and twist. Control power requirements can be high because of effectively short moment arms. The camber and twist are strongly dependent on trim stability margins. This aspect needs to be understood in detail when comparing different types of planforms. This paper covers three inter-related aspects – a wing design method, the suitability of solvers used with the method and a comparative study of two, typical UCAV planforms. This is inspired by the need to understand a variety of wings (in the public domain) that are, at first sight, aimed at similar missions. The main emphasis has been on developing and understanding cruise design camber and twist with Cm constraints of stable, neutral and unstable static margins. Spanwise lift and drag loadings have also been presented. Camber design has been via attained thrust methods and a modal approach. It is shown that starting from basic information such as the planform, we are able to predict the anticipated performance with sufficient confidence for comparative assessments of published project data. Further work is proposed in several areas.
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Considerations for UAV design and operation in South African airspace
01/10/2006
L. A. Ingham, T. Jones and A. Maneschijn
At present, the lack of UAV regulations and standards precludes UAVs from being certified to operate commercially in un-segregated civilian airspace. Because of strategic, economical and security requirements, it is necessary to devise a method to operate UAVs in South African airspace within existing regulatory arrangements. This paper suggests specific UAV missions, viz.; maritime patrol/boarder control, search & rescue, and cargo transport, together with design considerations and possible concepts of UAV; operations, maintenance and training, that will enable UAVs to satisfy the immediate South African strategic requirements whilst further UAV standards and regulations are being developed.
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Technical Note: Thermal buckling of a thin uniform circular disk: a comparison of predictions
01/10/2006
K. A. Seffen
The conditions for thermally-induced buckling of an unloaded thin, circular disk are compared from two well-known but unconnected studies: an approximate solution by Freund for a constant thickness disk, which must neglect the free edge condition, and an exact solution by Mansfield but only for a disk whose thickness tapers to zero in a particular manner. It is shown that buckling occurs at slightly higher values compared to a finite element analysis of a constant thickness disk but that the case of variable thickness seems to offer a closer result, which suggests that it better models the boundary layer behaviour near the free edge.
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Longitudinal flight control design with handling quality requirements
01/09/2006
D. Saussie, L. Saydy and O. Akhrif
This work presents a method for selecting the gain parameters of a control law for an aircraft’s longitudinal motion. The design incorporates various handling quality requirements involving modal, time- and frequency-domain criteria that were fixed by the aircraft manufacturer. After necessary model order-reductions, the design proceeds in essentially two-steps: Stability Augmentation System (SAS) loop design and Control Augmentation System (CAS) loop design. The approach partly relies on the use of guardian maps to characterize, in each case, the set of gain parameters for which desired handling quality requirements are satisfied. The approach is applied throughout the full flight envelope of a business jet aircraft and yields satisfactory results.
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Impact of solar storms on high altitude long endurance umanned aircraft and airship design and operations
01/09/2006
L. R. Newcome
This paper applies existing information on solar storms to unmanned aviation; no new research data is presented. The purpose of this paper is to alert the unmanned aviation community to the potential hazards posed by solar storms, to familiarize it with the effects of solar storms and how to mitigate them, and to encourage research on solar storm effects on high altitude long endurance (HALE) aircraft and airship design and operations. As unmanned aircraft and airships move increasingly into high altitude (50,000+ ft), endurance (24+ hr) roles, they will become vulnerable to the effects of space weather, specifically that of solar storms. Although solar storms are commonly associated with their impact on satellites, they affect the routing and timing of airline flights flying for 6 to 8 hr at 30,000 to 40,000 ft. Operating twice as high and with flight times twice as long (or longer) than those of airliners, HALE aircraft and airships occupy a middle zone of vulnerability, being more so than airliners but less so than satellites. A key difference however is that satellites are designed for space weather, whereas some current HALE vehicles are not. The paper concludes that unmanned HALE aircraft and airships can be one to three orders of magnitude more vulnerable to solar storms than a trans-Pacific airliner.
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Dynamics and control of single-line kites
01/09/2006
G. Sanchez
This paper presents a dynamic analysis of a single-line kite with two degrees of freedom. A Lagrangian formulation is used to write convenient equations of motion. The equilibrium states of the system and their stability are studied; eigenvalues and eigenmodes are calculated by using linear theory. The stability in the parametric plane delta - W0 is discussed, where delta defines the bridle geometry and W0 is wind velocity. The system goes through a Hopf bifurcation and periodic branches of solutions appear. The orbits and their stability have been calculated numerically using Floquet theory and wind velocity seems to play an important role in their existence. Finally the kite response against gusts is considered and an open loop control system developed to keep the flight altitude invariant under changing atmospheric conditions. Modifying the bridle's geometry seems to be a convenient way to control a kite's performance.
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Circular flight kite tests: converting to standard results
01/09/2006
J. C. Stevenson and K. V. Alexander
Kite testing by flying in a horizontal circle, was developed in order to address the inevitable accuracy problems inherent in pre-existing kite measurement techniques. However the raw results from this circular flight method are not directly comparable with traditional kite performance measurements. To enable direct comparisons to be made, modifying equations have been developed to convert the raw circular flight results into the traditional measurements of lift to drag ratio, and lift coefficient. This paper derives the modifying equations, and presents experimental results comparing traditional measurements with both the raw and modified circular flight results. The modifying equations are applied to an example set of results to assess the sensitivity of the test environment parameters. It is concluded that for many cases, the discrepancy between the raw circular flight test results and traditional measurement techniques is small enough to ignore. Alternatively, the modifying equations given in the paper may readily be encoded so that traditional results may be quickly obtained from this novel test method.
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Aerofoil profile and sweep optimisaton for a blended wing-body aircraft using a discrete adjoint method
01/09/2006
A. Le Moigne and N. Qin
Aerodynamic optimisations of a Blended Wing-Body (BWB) aircraft are presented. A discrete adjoint solver is used to calculate efficiently the gradients, which makes it possible to optimise for a large number of design variables. The optimisations employ either a variable-fidelity method that combines low- and high-fidelity models or a direct Sequential Quadratic Programming (SQP) method. Four Euler optimisations of a BWB aircraft are then presented. The optimisation is allowed to change a series of master sections defining the aircraft geometry as well as the sweep angle on the outer wing for two of the optimisations. Substantial improvements are obtained, not only in the Euler mode but also when the optimised geometries are evaluated using Reynolds-averaged Navier-Stokes solutions. Some interesting features of the optimised wing profiles are discussed.
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Aerodynamic effectiveness of the flow of exhaust gases in a generic formula one car configuration
01/09/2006
F. L. Parra and K. Kontis
The effects of the flow of exhaust gases intentionally orientated on the rear wing element of a generic Formula One car body have been studied. A qualitative analysis of the effectiveness of a cold nitrogen jet on a NACA 0012 type of aerofoil has been conducted. The Reynolds number of the jet was 13,000, based on the jet velocity and diameter, and of the bodywork was 54,000, based on the free stream velocity and bodywork length. The lift coefficient was measured via a three-component strain-gauge force balance at four different ground-to-aerofoil heights (32, 45, 60 and 90mm) and incidence range -20 to +20 degrees. The surface flow patterns were visualized using the oil flow technique and were compared with numerical simulations. Pressure measurements were conducted using pressure tappings. The CFD solver was FLUENT. The RNG k-e model was selected to solve the turbulent flow transport equations. The numerical study also comprised the investigation of the aspiration generated by exhaust gases when these are ejected inside a duct of greater diameter. A parametric investigation relating the relative diameter of exhaust pipe and outer duct and the relative overlap between the sides of the duct and the exhaust pipe was performed.
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Efficiency parameters for modern commercial aircraft
01/08/2006
R. K. Nangia
Currently, there is great emphasis, worldwide, on environmental issues. This will have an impact on civil aircraft design, manufacture and operation.
Since the advent of the jet engine and swept wing aircraft, the trends have naturally tended towards greater productivity through increasing speed and payload. The cruise speed of conventional civil aircraft is unlikely to increase beyond current levels. Further increases in productivity are achieved by increasing payloads. This has led towards larger aircraft with the capability for increased ranges. It is shown that designing aircraft for longer ranges increases fuel burn significantly.
A series of aircraft operational parameters have been analysed. Selected data and established trends for current and future aircraft are presented. The data has been interpreted into efficiency terms, relating payload, range, fuel consumed and a measure of unit costs. It is shown that ‘value’ (cost) and noise effective efficiencies decrease dramatically with increasing range.
Environmental and economic considerations, in the future, may well demand greater efficiency in preference to productivity. One solution for long-range services is to use short-range hops. Another is via air-to-air refuelling. This will be addressed, in more detail, in a future paper.
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Potential of reducing the environmental impact of aviation by using hydrogen Part I: Background, prospects and challenges
01/08/2006
F. Haglind (formerly Svensson), A. Hasselrot and
R. Singh
The main objective of the paper is to evaluate the potential of reducing the environmental impact of civil subsonic aviation by using hydrogen fuel. The paper is divided into three parts of which this is Part I, where the background, prospects and challenges of introducing an alternative fuel in aviation are outlined. In Part II the aero engine design when using hydrogen is covered, and in Part III the subjects of optimum cruising altitude and airport implications of introducing liquid hydrogen-fuelled aircraft are raised.
Looking at the prospect of alternative fuels, synthetic kerosene produced from biomass turns out to be feasible and offers environmental benefits in the short run, whereas hydrogen seems to be the more attractive alternative in the long run.
Powering aero engines and aircraft with hydrogen has been done successfully on a number of occasions in the past. Realising this technology change for a fleet of aircraft poses formidable challenges regarding technical development, energy requirement for producing hydrogen, handling, aircraft design and making liquid hydrogen economically compatible with kerosene.
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Civil aircraft design priorities: air quality? climate change? noise?
01/08/2006
P Brooker
A variety of related questions is posed. Are the right priorities for future aircraft design being set now? New civil aircraft types could be ‘silent’, i.e. make much less noise than current types. They could be ‘green’, i.e. safeguard the environment. Is silent as important as green? The crucial answer is that future aircraft design should focus on substantial reductions on climate change impact. The air quality targets proposed by the ‘Sustainable Aviation’ initiative appear very ambitious: they should be pursued only to the extent that they do not affect improved fuel efficiency and reduced climate-changing emissions. Good progress has already been made on the aircraft noise targets proposed by the ‘Sustainable Aviation’ initiative, but again they should be pursued only to the extent that they do not affect improved fuel efficiency and reduced climate-changing emissions. The financial case for designing to reduce aircraft noise in order to deliver novel financial benefits, e.g. increase airport flights at night and/or relocate airports, is weak.
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Towards a silent aircraft
01/08/2006
A.P. Dowling and T. Hynes
We set a target for a ‘Silent’ aircraft to be imperceptible outside the airfield perimeter in an urban environment, and then address conceptual designs to meet this requirement. Avoiding some traditional aircraft noise sources requires a radical rethink about the configuration. An all-lifting design has many benefits, enabling a closer integration of airframe and engine than the traditional ‘tube and wing’. Low-noise design includes taking advantage of shielding of engine noise by the airframe; low-noise engines with large, low speed jets; an order of magnitude increase in absorption by liners; and operations for low-noise informing the design. Progress to date on the Silent Aircraft Initiative is presented, along with some conceptual aircraft and engine designs. The further work needed to develop these into viable future aircraft is discussed.
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Civil aviation and the environment – the next frontier for the aerodynamicist
01/08/2006
J. J. Green
In the coming century, the impact of air travel on the environment will become an increasingly powerful influence on aircraft design. Unless the impact per passenger kilometre can be reduced substantially relative to today’s levels, environmental factors will increasingly limit the expansion of air travel and the social benefits that it brings. The three main impacts are noise, air pollution around airports and changes to atmospheric composition and climate as a result of aircraft emissions at altitude. The lecture will review the work done within the Air Travel – Greener by Design programme to assess the technological, design and operational possibilities for reducing these impacts. The main aeronautical disciplines all have something to contribute but it is in aerodynamics that the greatest opportunities appear to lie. If these opportunities are pursued, the aircraft in production in 2050 could be very different from those of 2005. It is for the aerodynamicists, supported by the structures and systems engineers and the materials scientists, to make the case for a radical leap.
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Greener manufacturing, maintenance and disposal – towards the ACARE targets
01/08/2006
J.J. Lee
This paper looks at how the aerospace industry can achieve the ACARE goal of greener manufacturing, maintenance and disposal. It looks further than merely reducing waste and eliminating hazardous materials and processes and suggests that the organisational structure of the industry will play an important role in facilitating a move towards such a goal. Greater co-operation or integration within the industry at all stages of the product life cycle chain is a fundamental requirement as individual companies run a risk of increasing the total environmental burdens if they concentrate solely on reducing their own impacts without considering the effect a change they make may have on other companies. The use of comprehensive environmental supply chain management systems and end of life plans can smooth the implementation of extended product responsibility and accelerate the benefits of greener manufacturing, maintenance and disposal.
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Küchemann’s weight model as applied in the first Greener by Design Technology Sub Group Report: a correction, adaptation and commentary
01/08/2006
J E Green
In the first report of the Greener by Design Technology Sub Group, the author made an error in deriving modern values for the empirical constants in the weight model, taken from Küchemann, that was used in the study of fuel efficiency of a range of aircraft designs. In this note the error is corrected and the weight model is also extended to take account of the observed variation with range of the ratio of design payload to maximum payload. This leads to the conclusion that the effect of design range on fuel efficiency is substantially greater than suggested in the Greener by Design report. The conclusion, which is in agreement with a correlation by Nangia of existing aircraft data, indicates that a modern aircraft with a design range of 15,000km burns approximately twice as much fuel per passenger-km as one with a design range of 4,000km. This powerfully reinforces the call made in the Greener by Design reports for in-depth studies to be made of the use of medium-range aircraft for long-distance travel.
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Integrating CFD and piloted simulation to quantify ship-helicopter operating limits
01/07/2006
D. M. Roper, I. Owen, G. D. Padfield
and S. J. Hodge
This paper describes a study which has been concerned with numerical predictions of the airwakes resulting from two simplified ship geometries: the internationally agreed Simple Frigate Shape, SFS1, and its successor, SFS2. Extensive steady-state simulations have been carried out for a wide range of wind conditions using Fluent, a commercially available Computational Fluid Dynamics (CFD) code. The CFD predictions have been partially validated against wind tunnel data produced by the National Research Council of Canada (NRC) and have shown good agreement. The resulting airwake velocity components have been exported from Fluent, interpolated onto suitable grids and attached to the FLIGHTLAB flight-simulation environment as look-up tables; piloted flight trials were then carried out using the Liverpool full-motion simulator. The pilot workload and helicopter control margins resulting from a range of wind-over-deck conditions have been used to develop the Ship-Helicopter Operating Limits (SHOL) for a Lynx-like helicopter and the SFS2. The workload was compared to the pilot’s experiences on a similar aircraft and a Type 23 Frigate and the simulated SHOL compared with SHOLs derived from sea trials. The results are very encouraging and open up further the long awaited prospect of such simulations being used in the future to reduce at-sea trials, and to provide a safe environment for pilot training.
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System of systems force structure optimisation
01/07/2006
M. S. McCoy
A system of systems study plan was developed and a prototype was executed to optimise a recommended military force structure. This methodology defined the optimal force structure, using constrained optimisation to reflect budget limitations and desired mission performance. The force structure included surface and air assets, a command, control, communications, computers, intelligence, surveillance and reconnaissance (C4ISR) architecture, and a recommended logistics infrastructure. A second aspect of the study plan defined the total acquisition strategy, which accounted for: retiring legacy assets, extending the service life of existing assets until new replacements became available, and acquiring new assets for deployment, within the budget allocation. This methodology combined various modeling and simulation techniques to meet three study objectives. First, a non-linear mixed integer programming model maximised performance, subject to cost constraints, cost as an independent variable (CAIV). Second, a dynamic programming model scheduled the transition from the legacy force structure to the future force, defined by the previous modeling technique. Third, a process simulation model simulated performance, over a one-year time period, for 25 areas of responsibility and five missions. This model verified performance estimates generated by the previous models.
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One CFD calculation to end point flight testing
01/07/2006
A. Cenko
Any time a new aircraft is introduced into service, or an old aircraft undergoes substantial modifications or needs to be certified to carry and employ new stores, the store separation engineer is faced with a decision about how much effort will be required to provide an airworthiness certification for the aircraft and stores. Generally, there are three approaches that have been used: wind-tunnel testing, computational fluid dynamics (CFD) analyses and flight testing. During the past twenty years there have been considerable advances in all three areas. In particular, there has been a considerable improvement in the speed and validity of CFD results for store separation. The Holy Grail of CFD has long been the reduction/replacement of wind-tunnel testing. This would mean in store separation the ability to go from a CFD calculation to flight testing at the end point. The paper will describe how this was achieved for the F/A-18C/Litening pod program.
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Boundary condition effects on the evolution of a train of vortex pairs in still air
01/07/2006
T. Yehoshua and A. Seifert
Effects of boundary conditions on the performance of compact oscillatory momentum and vorticity generators, commonly known as ‘synthetic jet’, ejecting a train of vortex-pairs into still air, were studied experimentally. The different boundary conditions altered the near-device entrainment process of the zero-net-mass-flux actuator. The measurements included hot-wire and Particle Image Velocimetry, cavity pressures and temperatures.
When the actuator operates in still air, a quasi-2D vortex pair is generated due to the extreme shear at the edges of the fluid slug ejected during the blowing stage of each excitation cycle. The vorticity flux exiting the slot determines the resulting vortex-pair circulation. The threshold slot exit velocity, for the current configuration and operating conditions, determines if the vortices will be sucked into the actuator’s cavity or be released. Once released, the vortex convection speed approximately scales with the peak velocity at the slot exit. However, the normalised convection velocity increases with the slot Reynolds number.
When even a very short extension is attached to one ‘lip’ of the actuator exit, the jet is deflected in the direction opposite the extended lip, due to the restriction on the entrainment process. When long, one ‘lip’ extension is attached, such that the vortex pair is ejected parallel to a plate, the coherence of the vortices improve, their phase speed and magnitude decrease.
The effects of high-frequency excitation, ejected perpendicular to a wall into still air, were also investigated. It was found that the presence of the plate does not have a measurable effect on the wall normal excitation, indicating that the majority of the entrainment is taking place from the forward 180° of the actuator exit plane. When the slot is inclined to the surface at a shallow angle of 30 degrees, an unsteady wall jet is formed, transferring momentum along the wall. This is a direct result of the symmetry break, altering the relative magnitudes of the vortex pair.
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Ordinal logistic regression analysis of flight task ratings
01/07/2006
R. Bradley and W. M. Maclaren
The relationship between a pilot workload rating for a simulated flight task in the proximity of an offshore platform helideck and three experimental factors – wind speed, wind direction and pilot is investigated. The statistical method employed is ordinal logistic regression, which allows the specifying and fitting of regression relationships between ordered categorical response variables and explanatory variables. The response variable in this context is a pilot’s rating of the workload induced by certain flight tasks, measured on an ordered categorical scale 1 to 10. Estimates of the effects of the explanatory variables are given and their practical significance discussed.
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The performance of round synthetic jets in quiescent flow
01/06/2006
M. Jabbal, J. Wu and S. Zhong
PIV measurements in the near-field region of a jet flow emanating from a round synthetic jet actuator into quiescent air were conducted over a range of operating conditions. The primary purpose of this work was to investigate the nature of synthetic jets at different operating conditions and to examine the jet flow parameters that dictate the behaviour of synthetic jet actuators. The effects of varying diaphragm displacement and oscillatory frequency for fixed actuator geometry were studied. It was observed that the characteristics of synthetic jets are largely determined by the Reynolds number and stroke length. An increase in the former is observed to increase the strength of consecutive vortex rings that compose a synthetic jet, whereas an increase in the latter results in an increase in relative vortex ring spacing and for further increases in stroke length, shedding of secondary vortices. Correlations were also made between the operating parameters and the performance parameters most effective for flow control and which therefore determine the impact of a synthetic jet on an external flow. Relations of time-averaged dimensionless mass flux, momentum flux and circulation with the jet flow conditions were established and found to widely support an analytical performance prediction model described in this paper. It is anticipated that the experimental data obtained in this study will also contribute towards providing a PIV database for macro-scale synthetic jet actuators.
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Minimum forebody drag in hypersonic continuum and rarefied flows
01/06/2006
J Pike
Minimum drag shapes of given length and base area are investigated for hypersonic flow using both Newtonian impact theory and free molecular flow theory. The drag of Newton’s minimum drag body, which has previously been evaluated by numerical means, is derived as an analytic expression. The analytical results are applicable to a range of local pressure laws allowing minimum drag shapes obtained using impact theory to be directly compared with low density flow equivalents using free molecular flow. The low density shapes are found to have larger blunt regions at the nose and significantly larger drag coefficients. For free molecular flow the drag varies with the surface reflection characteristics. As the fraction of diffuse reflection at the surface increases, the drag increases and the sensitivity of the drag to changes in the minimum drag shape is reduced.
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Experimental Investigations on the Application of Lift Enhancement Devices to Forward-Swept Aircraft
01/06/2006
Zhang W , Wang J, J and Wu Z
The force measurements were conducted in low speed wind tunnel to investigate the effects of the scale, shape and the installation type of Gurney flap on a forward-swept aircraft model. The results indicated that both rectangular and triangular Gurney flaps can enhance the lift coefficient of the model tested, but with a little decrease of stall angle from 38° to 36°. The lift and drag coefficients increased with the Gurney flap scales. Meanwhile, the triangular Gurney flap can improve the aerodynamic performance more effectively when its high side is located near the wing root than the reverse installation with the low side near the wing root and the high side near the wing tip. Additionally, for the same Gurney flap, the model with smaller forward-swept angle can generate higher lift-enhancement in comparison with the larger forward-swept angle model.
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Development of an aircraft systems dispatch reliability design methodology
01/06/2006
M. Bineid and J. P. Fielding
This paper describes the development of a generic aircraft systems dispatch reliability design methodology (ASDRDM) that has been developed for use during early phases of the aircraft systems design process.
The methodology incorporates prediction of both reliability and maintainability through the aircraft design hierarchy, down to component level. It can be applied at the early design stage, but can also be used for advanced design phases and can use generic or actual failure rate and mean time to repair data. It allows designers to modify system architectures and component reliability and maintainability characteristics. The paper shows the validation that has been performed, and its use is demonstrated by a case-study.
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Cumulative global metamodels with uncertainty – a tool for aerospace integration
01/06/2006
P. H. Reisenthel, J. F. Love, D. J. Lesieutre and R. E. Childs
The integration of multidisciplinary data is key to supporting decisions during the development of aerospace products. Multidimensional metamodels can be automatically constructed using limited experimental or numerical data, including data from heterogeneous sources. Recent progress in multidimensional response surface technology, for example, provides the ability to interpolate between sparse data points in a multidimensional parameter space. These analytical representations act as surrogates that are based on and complement higher fidelity models and/or experiments, and can include technical data from multiple fidelity levels and multiple disciplines. Most importantly, these representations can be constructed on-the-fly and are cumulatively enriched as more data become available. The purpose of the present paper is to highlight applications of these cumulative global metamodels (CGM), their ease of construction, and the role they can play in aerospace integration. A simple metamodel implementation based on a radial basis function network is presented. This model generalises multidimensional data while simultaneously furnishing an estimate of the uncertainty on the prediction. Four examples are discussed. The first two illustrate the efficiency of surrogate-based design/optimisation. The third applies CGM concepts to a data fusion application. The last example is used to visualise extrapolation uncertainty, based on computational fluid dynamics data.
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Comparison of Experimental and Numerical Investigation on a jet in a Supersonic Cross-Flow
01/06/2006
A. Kovar and E. Schülein
Flow interaction of three different jet configurations ejecting air from a flat plate into a supersonic cross flow were investigated experimentally and numerically. The test conditions encompassed a jet pressure ratio of P0j, P¥ = 100 at a Mach number of M¥ = 5 and Reynolds number of about Re¥ = 25 × 106 based on the length of the flat plate. The investigated test cases are: a) single jet; b) four jets positioned in-line in main flow direction; c) four jets positioned side-by-side in spanwise direction. The prediction of the overall flow phenomena as occurring within the interaction area was in fair agreement with the experiments, although quantitatively differences occur that will be discussed in the paper.
The results of the comparison are presented and the experimental data are used to validate the applied code.
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Rigid body separation dynamics for space launch vehicles
01/05/2006
B. N. Rao, D. Jeyakumar, K. K. Biswas, S. Swaminathan and E. Janardhana
This paper presents a systematic formulation for the simulation of rigid body dynamics, including the short period dynamics, inherent to stage separation and jettisoning parts of a satellite launcher. This also gives a review of various types of separations involved in a launch vehicle. The problem is sufficiently large and complex; the methodology involves iterations at successively lower levels of abstraction. The best choice to tackle such problems is to use state-of-the-art programming technique known as object oriented programming. The necessary classes have been identified to represent various entities in the launch vehicle separation process (e.g., gravity, aerodynamics, propulsion and separation mechanisms etc.). Simple linkages are modelled with suitable objects. This approach helps the designer to simulate a launch vehicle separation dynamics and also to analyse separation system performance. To examine the influence of the design variables on the separating bodies, statistical analyses have been performed on the upper stage separation process and pull out of ongoing stage nozzle from the spent stage of a multistage rocket carrier using retro rockets.
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EPISTLE: High lift system design for
01/05/2006
U. Herrmann
A new approach for low-drag high-lift system design based on the application of viscous flow solvers was developed in the EC research project EPISTLE. Two high-lift systems for a supersonic commercial transport aircraft (SCT) wing were designed, manufactured and wind-tunnel tested. The predicted large drag reductions were fully confirmed by tests at high Reynolds numbers. These drag reductions significantly reduce the low-speed noise of future SCT configurations. This was estimated by preliminary aircraft design tools. Low-speed noise reduction by aerodynamic means is obtained, as effective high-lift systems enable these aircraft to climb faster.
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Key aerodynamic technologies for aircraft engine nacelles
01/05/2006
S. Raghunathan, E. Benard, J. K. Watterson, R. K. Cooper, R. Curran, M. Price, H. Yao, R. Devine and B. Crawford, D. Riordan, A. Linton, J. Richardson and J. Tweedie
Customer requirements and vision in aerospace dictate that the next generation of civil transport aircraft should have a strong emphasis on increased safety, reduced environmental impact and reduced cost without sacrificing performance. In this context, the School of Mechanical and Aerospace Engineering at the Queen’s University of Belfast and Bombardier have, in recent years, been conducting research into some of the key aerodynamic technologies for the next generation of aircraft engine nacelles. Investigations have been performed into anti-icing technology, efficient thrust reversal, engine fire zone safety, life cycle cost and integration of the foregoing with other considerations in engine and aircraft design. A unique correlation for heat transfer in an anti-icing system has been developed. The effect of normal vibration on heat transfer in such systems has been found to be negligible. It has been shown that carefully designed natural blockage thrust reversers without a cascade can reduce aircraft weight with only a small sacrifice in the reversed thrust. A good understanding of the pressure relief doors and techniques to improve the performance of such doors have been developed. Trade off studies between aerodynamics, manufacturing and assembly of engine nacelles have shown the potential for a significant reduction in life cycle cost.
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Aeroelastic analysis through linear and non-linear methods: a summary of flutterprediction in the PUMA DARP
01/05/2006
N. V. Taylor, C. B. Allen, A. L. Gaitonde, D. P. Jones, G. A . Vio, J. E. Cooper, A. M. Rampurawala, K. J. Badcock, M. A. Woodgate, M. J. de C. Henshaw
This paper presents a comparison of linear and non-linear methods for the analysis of aeroelastic behaviour and flutter boundary prediction. The methods in question include NASTRAN and ZAERO, based on linear aerodynamics, and the non-linear coupled CFD-CSD methods RANSMB and PMB, developed at the Universities of Bristol and Glasgow respectively. The test cases used for this comparison are the MDO and AGARD 445.6 weakened wing. In general, it was found that the non-linear methods demonstrate excellent agreement with respect to pressure distributions, deflections, dynamic behaviour, and flutter boundary locations for both cases. This is in contrast to previous studies involving similar methods, where notable differences across the MDO span were found, and is taken to imply good performance of the CFD-CSD interpolation schemes employed here. While the linear methods produce similar flutter boundaries to the coupled codes for the aerodynamically simple AGARD 445.6 wing, results for the transonic ‘rooftop’ MDO wing design did not agree as well.
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CFD fire simulation of the Swissair Flight 111 in-flight fire – Part II: Fire spread analysis
01/05/2006
F. Jia, M. K. Patel, E. R. Galea, A. Grandison and J. Ewer
In 1998, Swissair Flight 111 (SR111) developed an in-flight fire shortly after take-off which resulted in the loss of the aircraft, a McDonnell Douglas MD-11, and all passengers and crew. The Transportation Safety Board (TSB) of Canada, Fire and Explosion Group launched a four year investigation into the incident in an attempt to understand the cause and subsequent mechanisms which lead to the rapid spread of the in-flight fire. As part of this investigation, the SMARTFIRE Computational Fluid Dynamics (CFD) software was used to predict the ‘possible’ development of the fire and associated smoke movement. In this paper the CFD fire simulations are presented and model predictions compared with key findings from the investigation. The model predictions are shown to be consistent with a number of the investigation findings associated with the early stages of the fire development. The analysis makes use of simulated pre-fire airflow conditions within the MD-11 cockpit and above ceiling region presented in an earlier publication (Part I) which was published in The Aeronautical Journal in January 2006(4).
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Impact of privatisation on the financial and economic performance of European airports
01/04/2006
Dr H.-A. Vogel
This paper assesses the financial performance of 35 European airports for the decade 1990 to 2000, comparing those subject to partial or full privatisation with those still in public ownership. In contrast to earlier research, the outcomes of partial factor productivity (PFP), financial ratio (FRA) and data envelopment analysis (DEA) are evaluated, in order to investigate differences attributable to the degree of privatisation. Changes in performance after a change in ownership structure are reviewed. The analysis of sample data reveals economically meaningful and statistically significant differences between publicly owned and privatised airports. The major differences lie in operating efficiency, capital productivity and capital structure. Although partially and fully privatised airports operate more efficiently, this does not translate into significantly higher returns on shareholders’ funds. Due to their at least indirectly government-backed credit standing, publicly owned airport companies can assume more debt relative to their respective equity. This results in considerably higher gearing and financial leverage, which compensates for the comparatively low return rate on assets.
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Corporate memory contribution to integrated design and analysis systems
01/04/2006
M. R. Mendenhall
The recent decline in the USA aerospace industry has resulted in fewer programs, fewer engineers, and a potential loss of capability for future technology development. As engineers retire or leave the industry, their corporate memory or retained knowledge must be preserved for future use. A process to capture their expert knowledge is described, and a framework which provides a means to retrieve and use this valuable technical information is shown. Four examples of integrated design and analysis systems for four diverse technologies and applications are discussed.
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An analysis of exit availability, exit usage and passenger exit selection behaviour exhibited during actual aviation accidents
01/04/2006
E. R. Galea, K. M. Finney, A. J. P. Dixon, A. Siddiqui and D. P. Cooney
The exits which passengers select in evacuation situations and the exits which are available post-crash is of great interest to aviation safety regulators who make rulings defining exit separation and aircraft evacuation certification, aircraft designers who develop the interior layout of aircraft cabins and position exits within the fuselage, cabin safety specialists who develop procedures for managing aircraft evacuation and cabin crew who must control aircraft evacuations. In this paper we examine issues associated with passenger exit selection behaviour and exit configurations frequently experienced during survivable crashes. This work makes use of the latest version of the Aircraft Accident Statistics and Knowledge database AASK V4.0, which contains information from 105 survivable crashes and over 2,000 survivors.
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Numerical calculation of separated flow past square and rectangular cylinders using panel technique
01/04/2006
A Roy and G. Bandyopadhyay
In the present investigation, a potential flow model based on panel method has been developed for calculation of two dimensional separated flows past square and rectangular cylinders. Free vortex lines are assumed to emanate from the points of separation that converge downstream of the body. The converged wake shape is iteratively obtained by integrating the velocity vectors at the collocation points. For solving separated flow past square and rectangular cylinders, four different versions of the solver have been developed for a wide range of incidence, namely, for zero, low, moderate and high angles of incidence. For validation of computed results, experimental investigations have been carried out in a low speed wind tunnel to obtain the surface pressure distribution on square cylinder and rectangular cylinder over a range of angles of incidence. Comparison is reasonably good.
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A dynamic sampling scheme for GPS
01/03/2006
S. Feng and W. Ochieng, D. Walsh and R. Ioannides
The Global Positioning System (GPS) is already being used for certain aviation applications and some safety critical air traffic services will be based on GPS. These air traffic services must achieve allowable levels of safety before they can be accepted. For this to occur, GPS based navigation systems must achieve a defined level of performance specified in terms of accuracy, integrity, continuity and availability. This must be determined by various analysis techniques including failure mode and effects analysis (FMEA) and integrity assessment. Because of the high percentile requirements placed on integrity (as the parameter most directly related safety), it is unfeasible to measure system performance by demonstration (field trial). Realistic simulation informed by some field experience is usually employed. However, the current simulation-based approaches for receiver autonomous integrity monitoring (RAIM) performance assessment have a number of weaknesses including the use of coarse (large) spatial and temporal sampling intervals, loose definitions of error and geometric correlations, a lack of sampling of all geometries and the inability to account for critical points due to uncorrelated factors.
This paper proposes a dynamic sampling method that takes account of these weaknesses, identifying dynamically only the required points for integrity performance assessment. Comprehensive simulations carried out to test the proposed approach for a single point, an area, and a non-precise approach (NPA) flight path to Gatwick airport in the United Kingdom show that the method can be effective in capturing all the points enabling a robust and reliable assessment of system integrity.
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A dynamic sampling scheme for GPS
01/03/2006
S. Feng, W. Ochieng, D. Walsh and R. Ioannides
The Global Positioning System (GPS) is already being used for certain aviation applications and some safety critical air traffic services will be based on GPS. These air traffic services must achieve allowable levels of safety before they can be accepted. For this to occur, GPS based navigation systems must achieve a defined level of performance specified in terms of accuracy, integrity, continuity and availability. This must be determined by various analysis techniques including failure mode and effects analysis (FMEA) and integrity assessment. Because of the high percentile requirements placed on integrity (as the parameter most directly related safety), it is unfeasible to measure system performance by demonstration (field trial). Realistic simulation informed by some field experience is usually employed. However, the current simulation-based approaches for receiver autonomous integrity monitoring (RAIM) performance assessment have a number of weaknesses including the use of coarse (large) spatial and temporal sampling intervals, loose definitions of error and geometric correlations, a lack of sampling of all geometries and the inability to account for critical points due to uncorrelated factors.
This paper proposes a dynamic sampling method that takes account of these weaknesses, identifying dynamically only the required points for integrity performance assessment. Comprehensive simulations carried out to test the proposed approach for a single point, an area, and a non-precise approach (NPA) flight path to Gatwick airport in the United Kingdom show that the method can be effective in capturing all the points enabling a robust and reliable assessment of system integrity.
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The development of a target-lock-on optical remote sensing system for unmanned aerial vehicles
01/03/2006
F-B Hsiao, T-L Liu, Y-H Chien, M-T Lee and R. Hirst
The use of unmanned aerial vehicles (UAVs) in various military and civil applications is the subject of much current attention. With recent developments in personal computer technology, and the availability at affordable cost of peripherals, and electronic and optical sensors, UAVs for long endurance missions, with flight autonomy beyond the visual range, have become an attractive challenge for study in universities and research institutes. This paper describes the development of a target-lock-on optical remote sensing system to be used as a payload in a university-class UAV. To accomplish autonomous way-point navigation for the conduct of optical sensing surveillance, a gimbaled-platform with servo control and an Attitude and Heading Reference System (AHRS) navigation system for UAV position and attitude measurements have been developed. The UAV also utilises a Global Position System (GPS) receiver, a pressure altimeter, gyroscopes and an electric compass. A novel mathematical model is proposed to calculate the optimal parameters for orientating the CCD camera line of sight with a ground target, designated in real time from a ground control station. Both ground and flight test results have demonstrated the feasibility of the navigation control scheme and the UAV’s ability to conduct ground target acquisition and image transmission.
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Benefits and design challenges of adaptive structures for morphing aircraft
01/03/2006
D. Moorhouse, B. Sanders, M. von Spakovsky and J. Butt
The purpose of this paper is to discuss the future of adaptive structures leading towards the concept of a fully morphing aircraft configuration. First, examples are shown to illustrate the potential system-level mission benefits of morphing wing geometry. The challenges of design integration are discussed along with the question of how to address the optimisation of such a system. This leads to a suggestion that non-traditional methods need to be developed. It is suggested that an integrated approach to defining the work to be done and the energy to be used is the solution. This approach is introduced and then some challenges are examined in more detail. First, concepts of mechanisation are discussed as ways to achieve optimum geometries. Then there are discussions of non-linearities that could be important. Finally, the flight control design challenge is considered in terms of the rate of change of the morphing geometry. The paper concludes with recommendations for future work.
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Predicting design induced pilot error using HET (human error template)
01/02/2006
N A Stanton, D Harris, P M Salmon, J M Demagalski, A. Marshall, M S Young and S W A Dekker
Human factors certification criteria are being developed for large civil aircraft with the objective of reducing the incidence of design-induced error on the flight deck. Many formal error identification techniques currently exist which have been developed in non-aviation contexts but none have been validated for use to this end. This paper describes a new human error identification technique (HET – human error template) designed specifically as a diagnostic tool for the identification of design-induced error on the flight deck. HET is benchmarked against three existing techniques (SHERPA – systematic human error reduction and prediction approach; human error HAZOP – hazard and operability study; and HEIST – human error In systems tool). HET outperforms all three existing techniques in a validation study comparing predicted errors to actual errors reported during an approach and landing task in a modern, highly automated commercial aircraft. It is concluded that HET should provide a useful tool as a adjunct to the proposed human factors certification process.
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Autonomy in unmanned air vehicles
01/02/2006
J. T. Platts
The paper describes a key risk area threatening the widespread deployment of unmanned air vehicles (UAVs), that of attaining high levels of autonomy. Autonomy is loosely defined in the context of UAVs and the meaning of ‘level of autonomy’ discussed. The paper argues that the achievement of high levels of autonomy is not merely a function of increasing machine intelligence but also of maintaining the human operator’s engagement with the decision making process and retaining human authority. An assumption is that a human being in the loop will be a requirement for safety, flight clearance and legal reasons on early systems. Therefore, developers of highly autonomous systems are presented with a paradox. It will be argued that the human must be placed at the centre of the design process and consequently human factors, the human machine interface and the system architecture become critical to achieving high levels of autonomy. This quality impacts on the entire knowledge acquisition and design cycle and broadens what is meant by that term placing it as a discipline firmly in the systems design community. The paper concludes by outlining the key barriers to the successful development of highly autonomous UAVs.
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On the vortex created by multiple blades joined at a hub
01/02/2006
P. R. Spalart
Experimental studies often use several blades, joined on the centreline, to generate a vortex in a wind tunnel. The circulation profile of this vortex is non-trivial, and a rapid prediction method will facilitate the design of such devices. Prompted by an experiment of Beninati and Marshall, such a model was derived. It assumes a large number of narrow blades and small turning angles, and rests on a balance of angular momentum and on simple aerofoil function. It is claimed to be valid even close to the centreline, can be completed analytically, contains no adjustable constants, and agrees well with two experiments although the turning angle reached 16° and the devices only had two or four blades. With typical geometries, the interference between blades makes the circulation profile quite different from that behind an elliptically-loaded wing, prompting some doubt over the relevance of such a vortex to those trailing real wings.
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A continuation design framework for nonlinear flight control problems
01/02/2006
T. S. Richardson and M. H. Lowenberg
A methodology referred to as the continuation design framework is developed for application to nonlinear flight control problems. This forms the basis of a systematic approach to control system design for aircraft operating in highly nonlinear regions of the flight envelope. The essence of the continuation design framework is to combine bifurcation analysis with modern control methods such as eigenstructure assignment. Theoretical and practical issues of the approach are discussed with particular reference to the problems posed by agile fighter aircraft. The proposed methodology is applied to a fifth order hypothetical aircraft model and is shown to provide a visible, flexible and logical approach to nonlinear aircraft control law design.
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BAE Systems/EPSRC integrated research programme in aeronautical engineering
01/02/2006
N. McDougall
BAE Systems and the Engineering and Physical Sciences Research Council (EPSRC) have recently formed a partnership to invest in strategic research in aerospace and defence. The framework which has been developed as part of this new alliance places a strong emphasis on collaboration. This contrasts with the conventional approach to industry led research which is normally based on the establishment of ‘centres of excellence’ in specific subject areas. By using a collaborative approach, the funding partners aim to benefit from inter-disciplinary collaboration which will take place during the project, giving rise to a more effective use of the invested funds.
The objective of the research programme is to develop technologies which would support the design of low cost (both to acquire and operate) flapless unmanned aerial vehicles (UAVs). This work includes fundamental aerodynamic research to provide control forces without the use of conventional flaps, coupled with developments in the areas of control systems, manufacturing engineering, structural engineering, the electromagnetic behaviour of these structures and design optimisation. The output from the research has been extended to include the design, manufacture, assembly and flight of a demonstrator vehicle, which will provide the research teams with a platform on which to evaluate the performance of their technology in a realistic flight environment. A total of fourteen research groups at ten universities are involved in the five year programme, which has a total value of £6×5M (€9×75M).
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Modern developments in hypersonic wind tunnels
01/01/2006
R. J. Stalker
The development of new methods of producing hypersonic wind- tunnel flows at increasing velocities during the last few decades is reviewed with attention to airbreathing propulsion, hypervelocity aerodynamics and superorbital aerodynamics. The role of chemical reactions in these flows leads to use of a binary scaling simulation parameter, which can be related to the Reynolds number, and which demands that smaller wind tunnels require higher reservoir pressure levels for simulation of flight phenomena. The use of combustion heated vitiated wind tunnels for propulsive research is discussed, as well as the use of reflected shock tunnels for the same purpose. A flight experiment validating shock-tunnel results is described, and relevant developments in shock tunnel instrumentation are outlined. The use of shock tunnels for hypervelocity testing is reviewed, noting the role of driver gas contamination in determining test time, and presenting examples of air dissociation effects on model flows. Extending the hypervelocity testing range into the superorbital regime with useful test times is seen to be possible by use of expansion tube/tunnels with a free piston driver.
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CFD Fire simulation of the Swissair flight 111 In-flight fire - Part1: Prediction of the pre-fire Air flow within the cockpit and surrounding areas
01/01/2006
E Galea
The SMARTFIRE computational fluid dynamics (CFD) software was used to predict the ‘possible’ behaviour of airflow as well as the spread of fire and smoke within a Swissair configured McDonnell Douglas MD-11 commercial transport aircraft. This work was undertaken by the Fire Safety Engineering Group (FSEG) of the University of Greenwich as part of Transportation Safety Board (TSB) of Canada, Fire & Explosion Group’s investigation into the in-flight fire occurrence onboard Swissair Flight 111 (SR111): TSB Report Number A98H0003. The main aims of the CFD analysis were to develop a better understanding of the possible effects, or lack thereof, of numerous variables relating to the in-flight fire. This assisted investigators in assessing possible fire dynamics for cause and origin determination. In Part 1, the numerical analyses to pre-fire airflow patterns within the cockpit and its vicinity are presented. The pre-fire simulations serve two ends. One is to provide insight into the flow patterns within the cockpit and its vicinity and further supportive numerical evidence for the airflow flight test observations. The other is to provide plausible initial flow conditions for fire simulations. In this paper, some flow patterns at a number of primary locations within the cockpit and its vicinity are highlighted and the predicted flow patterns are compared with the findings from the airflow flight tests. The predicted patterns are found to be in good qualitative agreement with the experimental test findings.
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Modelling the flight dynamics of the hang glider
01/01/2006
M V Cook and M Spottiswoode
The development of the non-linear equations of motion for the hang glider from first principles is described, including the complex geometry of control by pilot ‘weight shift’. By making appropriate assumptions the linearised small perturbation equations are derived for the purposes of stability and control analysis. The mathematical development shows that control is effected not by pilot weight shift, but by centre of gravity shift and that lateral-directional control by this means is weak, and is accompanied by significant instantaneous adverse response.
The development of a comprehensive semi-empirical mathematical model of the flexible wing aerodynamics is described. In particular, the modelling attempts to quantify camber and twist dependencies. The performance of the model is shown to compare satisfactorily with measured hang glider wing data obtained in earlier full scale experiments. The mathematical aerodynamic model is then used to estimate the hang glider stability and control derivatives over the speed envelope for substitution into the linearised equations of motion.
Solution of the equations of motion is illustrated and the flight dynamics of the typical hang glider are described. In particular, the dynamic stability properties are very similar to those of a conventional aeroplane, but the predicted lateral directional stability margins are significantly larger. The depth of mathematical modelling employed enables the differences to be explained satisfactorily. The unique control properties of the hang glider are described in some detail. Pitch and roll control of the hang glider is an aerodynamic phenomenon and results from the pilot adjusting his position relative to the wing in order to generate out of trim aerodynamic control moments about the centre of gravity. Maximum control moments are limited by hang glider geometry which is dependent on the length of the pilot’s arm. The pilot does not generate control moments directly by shifting his weight relative to the wing. The modelling thus described would seem to give a plausible description of the flight dynamics of the hang glider.
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Comparison of a grid-based CFD method and vortex dynamics predictions of low Reynolds number cylinder flows
01/01/2006
L. Baranyi and R. I. Lewis
Computational fluid dynamics models range from the finite difference type grid-based method to the Lagrangian style vortex cloud simulation technique for solving the Navier-Stokes equations. This paper undertakes a comparison of these two methods for the classical datum bluff body case of flow past a stationary circular cylinder at low Reynolds numbers in the range 10 to 220. Comparisons include time-history, time-mean and root-mean-square values of oscillating drag and lift coefficients, frequency of vortex shedding and related vortex street wake flow patterns. Particularly close agreement was obtained for Strouhal number versus Reynolds number, and good agreement for time-mean value of drag coefficients; comparison was also made with experimental results. Attempts are also made to calculate the skin friction and surface pressure components of the cylinder drag, revealing the significance of skin friction drag within this range and its relative insignificance above a Reynolds number of 220.
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A feasiblity study on designing model support systems for a blended wing body configuration in a transonic wind tunnel
01/01/2006
M. Maina, N. Corby, E. L. Crocker, P. J. Hammond and P. W. C. Wong
It is considered that the blended wing body may offer the possibility of improvements in performance efficiency over the conventional civil transport. Such configurations will require transonic wind tunnel testing. Hence, a feasibility study has been carried out at ARA to investigate possible model support systems that could be used for this purpose. The study addressed issues arising from the mechanical design of two support systems; namely, a blade or Z-sting and a standard rear sting. In particular, the relatively restricted space available within the model fuselage has presented challenges in the design of the layout of the balance and instrumentation required for the model. CFD analysis has been carried out to assess the relative interference effects of the two support arrangements. This initial work has shown unexpectedly significant interference effects associated with the Z-sting support and attention is drawn to the need for further design work to minimise these effects.
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Dynamic gain-scheduled control of the ICE 101-TV
01/12/2005
C. D. C. Jones, T. S. Richardson and M. H. Lowenberg
This paper shows the theoretical development and application of dynamic gain scheduled control – a novel method for the control of nonlinear systems – to an aircraft model. The idea behind this method is to schedule the control law gains with a fast varying state variable rather than with a slow varying state or an input parameter. This is advantageous as it is then possible to schedule the gains with a state variable that is dominant in the mode that we are most interested in controlling. The use of this type of gain scheduling is shown to improve the transient response of the aircraft model when stepping between trim conditions and to overcome some of the problems associated with conventional gain scheduled controllers (such as control surface position limit saturation). ‘Hidden coupling terms’ that introduce unwanted dynamics when scheduling gains with a fast state (rather than the input design parameter) are eliminated directly by applying a transformation to the classical parameter-scheduled gain distributions which are calculated using eigenstructure assignment. A second order longitudinal model and a 5th order longitudinal/lateral model of the ICE 101-TV tailless delta-wing aircraft configuration are used to demonstrate the design process.
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Solar-powered space flight
01/12/2005
M. H. D. Kemp
The aim of this paper is analyse the practicality or otherwise of solar-powered propulsion (after launch using conventional chemical rocketry) for a space vehicle’s late pre-orbital trajectory phase, for orbital transfer and for post-orbital flight. We introduce a ‘concept’ vehicle that in principle permits the use of solar-powered propulsion in each of these stages. Some of the technical challenges that such a vehicle might face are analysed, including the problem of how to keep a large ultra-low mass optical concentrator arrangement sufficiently accurately positioned in different parts of such a trajectory.
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Prediction of acoustic resonance phenomena for weapon bays using detached eddy simulation
01/12/2005
R. M. Ashworth
It is argued that acoustic resonance phenomena in open cavities such as weapons bays cannot be adequately predicted through numerical solution of Reynolds averaged Navier-Stokes (RANS) equations. The requirement to resolve the growth of the shear layer instability from the lip of the cavity inevitably implies that turbulence further downstream is resolved while also being modelled thus making RANS over dissipative. Large eddy simulation (LES) models only unresolved scales and a hybrid method combining RANS near walls with LES in the cavity appears a practical alternative to pure RANS. This paper compares computations of the M219 cavity configuration made with unsteady RANS and with the hybrid method known as detached eddy simulation (DES). It is shown that whilst unsteady RANS and DES give very similar predictions for the 1st and 3rd modes of the acoustic resonance the 2nd mode (which is dominant near the centre of the cavity) is absent in the RANS results but well predicted by DES. The 2nd mode is thought to arise from an interaction with vortical structures in the shear layer which are suppressed in the highly dissipative RANS method. The 4th mode, which is much weaker than the other three modes, is over-predicted by DES and under-predicted by a smaller amount in RANS.
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Optimum design for buckling of arbitrary shaped ribs under uncertain loadings
01/12/2005
A. C. Conrado, A. R. de Faria and S. F. M. de Almeida
Typically, aircraft wing structural panels are designed against buckling for a very large number of possible loadings that may occur during the operation of the aircraft. If the optimisation procedure accounts only for a limited number of design loads, the structure may be vulnerable to a specific type of loading that may cause the structure to fail. A novel approach for the optimisation of ribs or plates of arbitrary shapes under uncertain loads is proposed. The geometry of the rib is defined by a single closed spline or several connected splines. The loading distribution is not considered to be uniform but it is allowed to vary within an admissible set, conferring uncertainty to the applied loads. The admissible load space comprises distributed normal and shear loadings that can be represented through a collection of piecewise linear functions defined along the plate boundary. A special procedure is applied to handle the constraint that the loading must be self equilibrating. A minimax strategy is used to deal with the loading variability such that the resulting optimal design is able to withstand an entire class of linear piecewise loadings along the rib boundary. The refinement of the loading representation may be completely independent of the refinement of finite element mesh. The validity of the proposed approach is assessed by applying it to an aeronautical wing rib.
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Status and perspectives of laminar flow
01/12/2005
G. Schrauf
After identifying the ecological and economic drivers for use of laminar flow technology, we outline the mechanisms of laminar-turbulent boundary layer transition and review the status of natural laminar flow (NLF) and hybrid laminar flow control (HLFC). New ways to reduce the complexity of HLFC systems are presented, and the remaining steps to achieve technology readiness are discussed.
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Shock-wave induced instability in
01/11/2005
A. Bagabir and D. Drikakis
The paper presents an investigation of flow instabilities occurring in shock-wave propagation and interaction with the walls of an enclosure. The shock-wave propagation is studied in connection with perturbed and unperturbed cylindrical blasts, initially placed in the centre of the enclosure, as well as for three different blast intensities corresponding to Mach numbers Ms = 2, 5 and 10. The instability is manifested by a symmetry-breaking of the flow even for the case of an initially perfectly-symmetric blast. It is shown that the symmetry-breaking initiates around the centre of the enclosure as a result of the interaction of the shock waves reflected from the walls, with the low-density region in the centre of the explosion. The instability leads to fast attenuation of the shock waves, especially for smaller initial blast intensities. The computations reveal that the vortical flow structures arising from the multiple shock reflections and flow instability are Mach number dependent. The existence of perturbations of large amplitude in the initial condition strengthens the instability and has significant effects on the instantaneous wall pressure distributions. The computational investigation has been performed using high-resolution Riemann solvers for the gas dynamic equations.
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A civil aviation safety assessment model using a Bayesian belief network (BBN)
01/11/2005
R. Greenberg, S. C. Cook and D. Harris
In this paper we present a Bayesian belief network (BBN) socio-technical model for investigating the accident rate for multi-crew civil airline aircraft. The model emphasises the influence of airline policy and societal behaviour patterns on the pilots within the piloting system. The main claim of this paper is that a BBN can be used to bring most aviation safety-critical elements into a common quantitative safety assessment despite the unique problems posed by the very low probability of accidents. We support this claim by replicating certain phenomena such as the low accident rate, the difference between the ‘more’ and ‘less’ safe airlines and other statistical factors of civil aviation. In particular, the model succeeds in explaining the large gap of six to seven orders of magnitude between in-flight measurements of pilots’ error and accident rate.
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Normal shock wave/turbulent boundary-layer interaction control using ‘smart’ piezoelectric actuators
01/11/2005
J. S. Couldrick, S. L. Gai, J. F. Milthorpe and K. Shankar
This paper looks at active control of the normal shock wave/turbulent boundary layer interaction (SBLI) using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, thus reducing wave drag. Active control allows optimisation of the interaction, as it would be capable of either positioning the control region around the original shock position using a series of unimorph flaps or fixing the shock position by controlling the rate of mass transfer.
The level of control achieved by unimorph piezoelectric actuators is not large because of small amounts of deflection possible. It is believed that to provide optimal control a piezoelectric material, which can provide greater strain and hence higher amounts of deflection is needed. However, currently such a piezoelectric material is not commercially available.
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A theoretical description of viscous flow along a flat plate
01/11/2005
R. C. Hastings
Theoretical quantification of viscous effects in fluid flows is difficult, even if turbulence is absent, except when it is legitimate to simplify the Navier-Stokes equations in some way; for example by invoking the boundary-layer approximation in appropriate cases of interacting viscous and inviscid flow. The technical importance of viscous effects was thought sufficient incentive to re-examine a very simple flow configuration – namely plane, uniform and steady flow of an incompressible, viscous fluid toward a vanishingly-thin flat plate aligned with the undisturbed stream – in search of fresh insights into the general theory for viscous-inviscid interactions.
The strategy was to exploit the analogy between vorticity transport in a viscous fluid and heat conduction in a moving solid. The key to doing so was the realization that, if the perturbation of the undisturbed flow by the plate might be represented as the sum of a series of successive approximations, then the stream function of the viscous part o
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The birth of the practical aeroplane: An appraisal of the Wright Brothers achievements
01/10/2005
G. D. Padfield and B. Lawrence
In this second Aeronautical Journal paper providing a technical appraisal of the Wright brothers’ achievements, the authors use modelling and simulation and associated flight dynamics analysis to present the development of the first practical aeroplane. The aircraft in question, the Wright Flyer III, was deemed fit for service by the Wrights in October 1905, and had evolved significantly from the first powered aircraft of 17 December 1903. The appraisal tries to shed light on many of the flight handling problems that the Wright brothers faced during this, their third phase of aeronautical endeavour, in 1904 and 1905. They retained their unstable configuration born in the 1901 and 1902 gliders, gradually refining the performance and handling until they considered the aircraft was ready for market. Their process of refinement has been reconstructed in simulation within the Liverpool Wright project, highlighting the many important developments during a period when Wilbur and Orville’s own documentation was limited. Apart from their engineering excellence, the Wright brothers are to be acknowledged for their perseverance and resolve in overcoming setbacks, for their ability to innovate and to recover and learn from their mistakes. In many ways the Wright brothers represent a model for the modern aeronautical engineer, and it is hoped that their legacy will be better preserved through the documentation of this project.e
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PIV measurements in a twin-jet STOVL fountain flow
01/10/2005
P. M. Cabrita, A. J. Saddington and K. Knowles
Mean velocity and first order turbulence measurements were obtained from a three-dimensional upwash fountain flow generated by the impingement of two compressible axisymmetric turbulent jets onto a normal plane. The jet impingement area and fountain formation regions were examined with data obtained through the use of particle image velocimetry. Seven configurations with different nozzle pressure ratios were considered to ascertain the influence of jet compressibility on the fountain development. Results indicate that the mixing of the fountain is dependent on the nozzle pressure ratio, leading to an increase in the fountain spreading rate with increase in nozzle pressure ratio.
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The behaviour of circular synthetic jets in a laminar boundary layer
01/10/2005
S. Zhong, F. Millet, and N. J. Wood
Dye flow visualisation of circular synthetic jets was carried out in laminar boundary layers developing over a flat plate at a range of actuator operating conditions and freestream velocities of 0·05 and 0·1ms–1. The purpose of this work was to study the interaction of synthetic jets with the boundary layer and the nature of vortical structures produced as a result of this interaction. The effects of Reynolds number (Re), velocity ratio (VR) and Strouhal number (St) on the behaviour of synthetic jets were studied. At low Re and VR, the vortical structures produced by synthetic jets appear as highly stretched hairpin vortices attached to the wall. At intermediate Re and VR, these structures roll up into vortex rings which experience a considerable amount of tilting and stretching as they enter the boundary layer. These vortex rings will eventually propagate outside the boundary layer hence the influence of the synthetic jets on the near wall flow will be confined in the near field of the jet exit. At high Re and VR, the vortex rings appear to experience a certain amount of tilting but no obvious stretching. They penetrate the edge of the boundary layer quickly, producing very limited impact on the near wall flow. Hence it is believed that the hairpin vortices produced at low Re and VR are likely to be the desirable structures for effective flow separation control. In this paper, a vortex model was also described to explain the mechanism of vortex tilting.
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Progress toward CFD for full flight envelope
01/10/2005
E. N. Tinoco, D. R. Bogue, T-J. Kao, N. J. Yu, P. Li and D. N. Ball
The value of computational fluid dynamics, CFD, delivered to date has mainly been related to its application to high-speed cruise design. To increase its applicability CFD must apply to the full flight envelope frequently characterised by large regions of separated flows. These flows are encountered by transport aircraft at low speed with deployed high lift devices, at their structural design loads conditions, or subjected to in-flight upsets that expose them to speed and/or angle-of-attack conditions outside the envelope of normal flight conditions to name a few. Such flows can only be characterised by the Navier-Stokes equations. This paper will report the progress toward CFD for full flight envelope. The CFD methods in use at Boeing will be described. Examples presented will address high-lift, loads and stability and control concerns including Reynolds scaling from wind tunnel to flight, vortex generator simulation, spoiler and horizontal tail effectiveness. In general, results shown are in ‘good enough’ agreement with experimental data. Deficiencies and the need for further algorithm and process improvement are noted. The need for automation to enable the large scale use of CFD will also be discussed.
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Design of composite helicopter rotor blades to meet given cross-sectional properties
01/10/2005
S. L. Lemanski, P. M. Weaver, G. F. J. Hill
This paper examines the design of a composite helicopter rotor blade to meet given cross-sectional properties. As with many real-world problems, the choice of objective and design variables can lead to a problem with a non-linear and/or non-convex objective function, which would require the use of stochastic optimisation methods to find an optimum. Since the objective function is evaluated from the results of a finite element analysis of the cross section, the computational expense of using stochastic methods would be prohibitive. It is shown that by choosing appropriate simplified design variables, the problem becomes convex with respect to those design variables. This allows deterministic optimisation methods to be used, which is considerably more computationally efficient than stochastic methods. It is also shown that the design variables can be chosen such that the response of each individual cross-sectional property can be closely modelled by a linear approximation, even though the response of a single objective function to many design parameters is non-linear. The design problem may therefore be reformulated into a number of simultaneous linear equations that are easily solved by matrix methods, thus allowing an optimum to be located with the minimum number of computationally expensive finite element analyses.
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Effects of leading edge cross-sections on the aerodynamic characteristics for flow over non-slender delta wing
01/08/2005
J Wang and S Lu
The aerodynamic performances of a non-slender 50° delta wing with various leading-edge bevels were measured in a low speed wind tunnel. It is found that the delta wing with leading-edge bevelled leeward can improve the maximum lift coefficient and maximum lift to drag ratio, and the stall angle of the wing is also delayed. In comparison with the blunt leading-edge wing, the increment of maximum lift to drag ratio is 200%, 98% and 100% for the wings with relative thickness t/c = 2%, t/c = 6.7% and t/c = 10%, respectively.
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Studies of capacity estimation of the airport with two parallel runways
01/08/2005
C Yihua, Y Chen and Y Zhou
The analytical capacity models of an airport with two runways system are developed in this paper and the theoretical capacity curves yielded by this model are analysed. The statistic airport capacity estimation methodology based on historical data is introduced as well. Both analytical models and statistic strategy are applied to estimate the capacity of the two runways system of a typical airport. Two sets of airport capacity curves obtained in different ways are compared and analysed. The result of the analysis indicates that the mathematical model works effectively in a fairly accurate way in the estimation of airport capacity.
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Bio-inspired design of flapping-wing micro air vehicles
01/08/2005
K D Jones, C J Bradshaw, J Papadopoulos and M F Platxer
In this paper the development and flight testing of flapping-wing propelled, radio-controlled micro air vehicles are described. The unconventional vehicles consist of a low aspect ratio fixed-wing with a trailing pair of higher aspect ratio flapping wings which flap in counterphase. The symmetric flapping-wing pair provides a mechanically and aerodynamically balanced platform, increases efficiency by emulating flight in ground effect, and suppresses stall over the main wing by entraining flow. The models weigh as little as 11g, with a 23cm span and 18cm length and will fly for about 20 minutes on a rechargeable battery. Stable flight at speeds between 2 and 5ms–1 has been demonstrated, and the models are essentially stall-proof while under power. The static-thrust figure of merit for the device is 60% higher than propellers with a similar scale and disk loading.
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Numerical simulation of rim seal flows in axial turbines
01/08/2005
J Boudet, V N D Autef, J W Chew, N J Hills and O Gentilhomme
In a gas turbine, ingestion of hot gas into the high-pressure turbine disc cavities could cause metal overheat. To prevent this, cool air is taken from the compressor and ejected through the cavities. However, this sealing flow also reduces the overall efficiency, and a compromise has to be found between the level of ingestion tolerated and the losses. Recent advances made in applying Computational Fluid Dynamics to such configurations are presented, with the aim of better understanding the physical phenomena and providing reliable design tools. First, results showing the pumping effect of the rotating disc are presented, including the influence of flow instabilities observed in both computational and experimental results. Second, the influence of the main annulus pressure asymmetries are analysed on a simplified representation of an available experiment, showing the combined influence of asymmetries generated by vanes and struts. Finally, a rim seal geometry representative of aero-engine design is studied in comparison to experiment, exhibiting the coupled influence of the cavity instabilities and annulus asymmetries.
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Development of an airship for tropical rain
01/08/2005
G. E. Dorrington
The design, manufacture and testing of a 480 cubic metre helium-filled airship, or dirigible balloon, intended for flight above tropical rain forest canopy is outlined. The requirements for the airship and the preliminary sizing method are set-out. Details of the final design and flight test results are included, as well as suggestions concerning future work. Particular attention is paid to the issue of accurate station-keeping and operation close to the canopy with winds present. It is concluded that the development of a truly useful aerial platform for canopy biological studies requires further research in aerodynamics, dynamic simulation and ultra-quiet propulsion systems.
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A Numerical study on mixing with air and hydrogen in scramjet combustor
01/07/2005
M Ali and T Fujiwara
A numerical study on mixing of air and hydrogen is performed by solving two-dimensional full Navier-Stokes equations. The main stream is air of Mach 5 entering through the configured inlet of the combustor and gaseous hydrogen is injected from the configured jet on the side wall. Supersonic mixing and diffusion mechanisms of a transverse hydrogen jet in two-dimensional finite air streams have been analyzed and discussed. The computed results are compared with the experimental data and show good agreement. For an otherwise fixed combustor geometry, the air inlet width and injection angle are varied to study the physics of mixing and flow field characteristics. On the effect of inlet width variation, two competing phenomena have been observed: (i) upstream of injector the strength of recirculation is higher for wider inlet and consequently the mixing increases, and (ii) downstream, the diffusion of hydrogen decreases with the increase of inlet width and eventually mixing decreases. As a result, in far downstream the mixing efficiency increases up to certain inlet width and then decreases for further increment of inlet width. For the variation of injection angle results show that upstream of injector the mixing is dominated by recirculation and downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60° and 90°. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.
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Computational fluid dynamics study of unconventional air vehicle configerations
01/07/2005
R Ramamurti, W Sandberg, P Vaiana, J Kellogg and D Cylinder
Two unconventional micro air vehicles developed by the Naval Research Laboratory are described. One of the vehicles employs flapping wings which is inspired by the flight of birds or insects but does not copy it directly. The second vehicle is a stop-rotor hybrid vehicle employing a pair of single blade, rotary/fixed wing panels, attached at their roots to separate coaxial shafts. An unstructured grid based incompressible flow solver, called feflo, is used to simulate the flow past these novel configurations in order to determine the flight characteristics of these vehicles.
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Semi-optimal co-ordinated manoeuvres for aircraft conflict resolution
01/07/2005
J. Parastari and M. B. Malaek
In this manuscript, a new concept of 2D-semi-optimal-circular-3-arced-path manoeuvres with constant speed for multiple aircraft co-operative conflict resolution is presented. This type of manoeuvres is based on appropriate commands to heading, speed and manoeuvreing time. According to aircraft turning dynamics, each aircraft manoeuvre is composed of three tangent circular arcs. The optimality of manoeuvres is based on the minimisation of weighted sum of kinetic energy for aircraft two-legged manoeuvres. In comparison, aircraft with lower weight factors bear more responsibility to resolve the conflicts. The effectiveness of the proposed algorithm for real time conflict resolution is guaranteed, where the number of encountering aircraft is less than five. Otherwise, the current method could also be jointed to one of the fast resolution methods, like probabilistic resolution algorithm or genetic algorithm – as a tool to choose the convex domain – to become more computationally effective. Considerable number of case studies has been done to evaluate the effectiveness of the proposed methodology, while some are presented in the paper.
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Low frequency behaviour of the subsonic doublet lattice method
01/06/2005
L. van Zyl
The results of the subsonic doublet lattice method (DLM), i.e. generalised unsteady aerodynamic forces (GAFs) at a set of reduced frequencies, are often used as input to the solution of the flutter equation. Solutions of the flutter equation are usually required at many more reduced frequencies than GAFs are calculated for by the DLM and some form of interpolation is therefore required. In the p-k formulation of Rodden, Harder and Bellinger, the imaginary part of the GAFs appear as QI/k, i.e. the imaginary part of the GAFs divided by the reduced frequency. In the case of real (i.e. non-oscillatory) roots of the flutter equation, the solution is determined entirely by the steady GAFs and the limiting value of QI/k at zero frequency. This is also true of the g-method of flutter solution as the two formulations are equivalent at k = 0. Expressions are derived for calculating the limiting values of QI/k directly from the DLM, thereby making the real roots independent of the interpolation of the GAFs. The exact way in which the low frequency DLM results are interpolated has a small effect on the interpolation quality in the case of the p-k flutter equation, whereas it has a significant qualitative effect on the results of the g-method of flutter solution of Chen.
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A novel approach to encouraging proper fatigue management in British Army aviation training and operations
01/06/2005
R. P. King
Fatigue management in military aviation remains problematic and can be easily neglected by planners and aircrew in a busy operational environment. The basic assessment tool (BAT) is an objective and educational computer tool for evaluating and combining various fatigue factors. It provides an impartial performance comparison while at the same time educating and reminding its users of the importance of fatigue management. Individual factors of the BAT were chosen because they affect fatigue, sleepiness, alertness and performance. A short explanation of components not chosen is also included. An example of how the BAT can be used is described and figures of the resulting outputs (screenshots) are included. Most commercial fatigue estimation products are subjective and do not consider specific issues associated with tactical operations in a field environment. This novel approach can be used to help plan missions by minimizing the BAT score while still maximising the tactical advantage and keeping fatigue management fresh in the minds of military rotary wing pilots while in training and on operations. Although the BAT is military aviation focused and objective, it can be easily modified to suit particular fatigue concerns.
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Acoustic validation of a new code using particle wake aerodynamics and geometrically-exact beam structural dynamics
01/06/2005
F Nitzsche and D G Opoku
This paper describes the validation of a new code for prediction both aeroacoustic and aeroelastic behaviour of hingeless rotors. The structural component is based on a non-linear beam element model considering small strains and finite rotations, which uses a mixed variational intrinsic formulation. The aerodynamic component is built on a low-order panel method incorporating a vortex particle free-wake model. The aerodynamic and structural components are combined to form a closely coupled aeroelastic code that solves in the time-domain. The loading and thickness noise terms for the aeroacoustic calculations are calculated from the aerodynamic data using a formulation based on the Ffowcs Williams-Hawkings (FW-H) equation. The code is successfully validated for acoustic signature and BVI predictions using test cases from the HELINOISE program.
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Equipment failures in ATC: Finding an appropriate safety target
01/06/2005
B. Subotic, W. Ochieng and A. Majumdar
The aviation community is currently faced with various approaches for the determination of Target Levels of Safety (TLS). The targets are usually derived for a specific airspace region, for a specific type of operation or a specific phase of flight. Therefore, current practices support the determination of TLS for specific aviation components in isolation. This paper argues that the setting of a new safety target for aviation has to be driven by an integrated system approach. Relevant past research on TLS is reviewed and augmented with the results from operational reports from two countries. A possible safety target for the year 2020 is suggested and scoped down to estimate the safety budget for air traffic control (ATC) equipment. The paper concludes with a discussion of the results and recommends useful practices to achieve the proposed integrated safety approach.
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Kite performance testing by flying in a circle
01/06/2005
J Stevenson K Alexander P Lynn
With the advent of recreational sports like kite surfing and buggying, the performance of kites has become a market driven item. Producers increasingly require methods to measure and improve the performance of the kites they manufacture. The Mechanical Engineering Department at the University of Canterbury has been working with a local kite producer to develop testing procedures suitable for kite manufacturers. The primary performance measurement is the lift to drag ratio. An early test rig was mounted in the top of a car, but limitations inherent in the design meant that it lost precision as the lift to drag ratio approached that of more advanced kites. This led the investigators to look for alternatives, and resulted in the development of the circular flight method. This method allows the test apparatus to be tuned to the performance of each kite, significantly improving the precision of the results while reducing the time taken for each test. In their raw form, the L/D results are not quite the same as those of the more traditional methods. But they reflect the underlying aerodynamic characteristics, and when used comparatively they can be used in the kite development process. Alternatively, with suitable processing the circular flight results can be converted to the traditional forms.
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Limited life engines for UAVs
01/05/2005
I. K. Clark
The ever expanding range of applications for unmanned air vehicles covers a wide variety of powerplant requirements. While many vehicles are high value assets and demand similar powerplant attributes to a conventional manned aircraft, there is an emerging requirement for powerplants which are designed to a limited life philosophy. This covers a range of applications: at the simplest level there are vehicles where the mission definition dictates that attrition rates will be high, for
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Simulation and flight test of a temperature sensing stabilisation system
01/04/2005
P. Herrmann and C. Bil
Thermopile sensors detect electromagnetic radiation as a function of the object’s temperature. Because there is a temperature difference between the cold ground and the warm sky, these sensors could be used to detect the horizon and thus be used as a reference to stabilise a small aircraft, such as an unmanned aerial vehicle (UAV) in visual meteorological conditions (VMC). To verify this hypothesis, a system has been developed providing horizon detection using thermopile sensors to stabilise an R/C model aircraft. The aircraft has gone through a number of flight trials using remote control to enable and disable the stabilisation system. During the flight trials the aircraft was set at various attitudes when the system was enabled. The stabilisation system was able to assume wing level under various bank angles and weather conditions with minimum overshoot and oscillation.
Although the system shows good performance during flight trials, most of the original design was done using trial and error. A design tool was needed to implement further improvements to the system and to efficiently implement it on other aircraft. This required a good understanding of the physical behaviour of the system and the interaction between the sensors, aircraft and the environment. A mathematical model of the overall system was developed using the MATLAB/Simulink environment to simulate the behaviour of the system under various conditions. The simulation results were then compared with actual flight experiments. This paper describes the modelling techniques used for the different system components and the results of the simulation compared to actual flight trials.
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Experiments on the hypersonic turbulent shock-wave/boundary-layer interaction and the effects of surface roughness
01/04/2005
S A Prince, M Vannahme and J L Stollery
An experimental investigation was performed to study the effects of surface roughness on the Mach 8×2 hypersonic turbulent shock-wave–boundary-layer interaction characteristics of a deflected control flap configuration. In particular, the surface pressure and heat transfer distribution along a quasi-2D ramp compression corner model was measured for flap angles between 0° and 38°, along with a Schlieren flow visualisation study. It was found that surface roughness, of scale 10% of the hinge-line boundary layer thickness, significantly increased the extent of the interaction, while increasing the magnitude of the peak pressure and heat flux just aft of reattachment. The incipient separation angle for a fully turbulent, Mach 8×2 boundary layer with a hinge line Reynolds number of 1×44 × 106, was estimated at 28-29°, reducing to between 19-22° with the introduction of laminar sub-layer scale surface roughness.
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Trade disputes in the commercial aircraft industry: A background note
01/04/2005
K. Hayward
The long-running debate between the US and the EU over government supports for large commercial aircraft has recently boiled over into a major dispute involving the World Trade Organisation (WTO). While the two sides have currently backed off from what could be a very damaging WTO outcome, there are still wide differences over the legitimacy of government supports (direct or indirect) for Airbus and Boeing airliners. This paper:
· Describes the background to the current dispute.
· Analyses the 1992 US–EU Agreement on Large Aircraft Subsidies.
· Outlines the WTO Agreement on Subsidies and Countervailing Measures and the decision by the US to mount an action under the WTO complaints procedures against launch investment for Airbus and the EU’s counter claim against Boeing.
· Considers the precedents set by the WTO rulings on the Brazilian–Canadian dispute over regional jet supports.
· Summarises the US–EU complaints to the WTO.
· Considers potential outcomes and the implications for the civil aerospace industry on both sides of the Atlantic.
· Analyses the wider issues surrounding government intervention in the aerospace sector.
The paper views the dispute as a reflection of fundamental differences, based primarily on divergent economic doctrines and values, between the US and the EU states. There could be especially damaging consequences for the EU should the WTO rule against the systems of repayable launch investment used by the Airbus governments. But both sides could lose heavily from the affair and there is a good case for maintaining some form of direct government intervention in civil aerospace technology acquisition, even near market research, in support of environmental sustainability objectives.
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Collision avoidance within flight dynamics constraints for UAV applications
01/04/2005
R. W. Penney
Avoiding collisions with other aircraft is an absolutely fundamental capability for semi-autonomous UAVs. However, an aircraft avoiding moving obstacles requires an evasive tactic that is simultaneously very quick to compute, compatible with the platform’s flight dynamics, and deals with the subtle spatio-temporal features of the threat.
We will give an overview of a novel prototype method of rapidly generating smooth flight-paths constrained to avoid moving obstacles, using an efficient trajectory-optimisation technique. Obstacles are described in terms of simple geometrical shapes, such as ellipsoids, whose centres and shapes can vary with time. The technique generates a spatio-temporal trajectory which offers a high likelihood of avoiding the volume in space-time excluded by the predicted motion of each of the known obstacles. Such a flight-path could then be passed to the aircraft’s flight-control systems to negotiate the threat posed by the obstacles. Results from a demonstration implementation of the collision-avoidance technique will be discussed, including non-trivial scenarios handled well within 100ms on a 300MHz processor.
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Dye visualisation of inclined and skewed synthetic jets in a cross flow
01/03/2005
S. Zhong, L. Garcillan and N. J Wood
Dye visualisation of both inclined synthetic jets and skewed synthetic jets was undertaken in a cross-flow experiment and the results were compared with those of normal synthetic jets. The process of vortex roll-up near the orifice exit and how the structure develops and interacts with the cross-flow as it propagates downstream was investigated so as to obtain an understanding of the effect of orifice orientation on the behaviour of synthetic jets. The effects of varying Reynolds number, velocity ratio and Strouhal number due to changes in diaphragm displacements and freestream velocities on the characteristics of synthetic jets were also examined. It is observed that in comparison to the normal jets vortical structures produced by both inclined and skewed jets tend to stay closer to the near wall region where maximum flow control effect is required. In both cases, at a relatively low Reynolds number and velocity ratio the active structures produced by the synthetic jet appear to be hairpin vortices which turn into vortex rings that migrate away from the wall as the Reynolds number and velocity ratio increase. These hairpin vortices are persistent in the near wall region hence are believed to be desirable structures for delaying flow separation.
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Neuro-fuzzy approach for performance optimisation of variable nozzle turbofan engine
01/03/2005
T R Nada A A Hashem
An algorithm employing adaptive neuro-fuzzy online identification and sequential quadratic programming optimisation techniques is developed to enhance aircraft engine performance. This algorithm is implemented and tested using digital simulation for two spool, mixed exhaust, variable geometry turbofan engine. Parametric study is conducted to select the proper measurable parameter that can represent the actual thrust during online optimisation. Subtractive clustering technique is applied to generate the minimum number of fuzzy rules that can model the engine performance at various input parameters and flight conditions. The resulting neuro-fuzzy system is then optimised through training algorithm to accurately represent the engine. This system can address engine variations by relearning the network using online measurements from the actual engine. Generating the optimum schedules and comparing them with those obtained from the complete non-linear engine model verify the algorithm. Benefits from this algorithm include fuel consumption savings, reductions in turbine inlet temperature, and preventing limit exceeding.
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Jet thrust vectoring using a miniature
01/03/2005
G Raman, S Packiarajan, G Papadropulos, C Weissman and S Raghu
This paper presents a new approach to vectoring jet thrust using a miniature fluidic actuator that provided spatially distributed mass addition. The fluidic actuators used had no moving parts and produced oscillatory flow with a square wave form at frequencies up to 1·6kHz. A subsonic jet with an exit diameter of 3·81cm was controlled using single and dual fluidic actuators, each with an equivalent circular diameter of 1·06mm. The fluidic nozzle was operated at pressures between 20·68 and 165·47kPa. The objectives of the present work included documentation of the actuation characteristics of fluidic devices, assessment of the effectiveness of fluidic devices for jet thrust vectoring, and evaluation of mass flow requirements for vectoring under various conditions. Measurements were made in the flow field using a pitot probe for the vectored and un-vectored cases. Some acoustic measurements were made using microphones in the near-field and for selected cases particle image velocimetry (PIV) measurements were made. Thrust vectoring was obtained in low speed jets by momentum effects with fluidic device mass flow rates of only 2 × 10–4kg/sec (0·6% of main jet mass flow per fluidic oscillator). Although a single fluidic device produced vectoring of the primary jet, the dual fluidic device configuration (with two fluidic devices on either side of the jet exit) produced mass flux enhancement of 28% with no vectoring. Our results indicate that fluidic actuators have the potential for use in thrust vectoring, flow mixing and industrial flow deflection applications.
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Industry applications of advanced flow diagnostics-expereience in the BAE systems ground effects rig
01/03/2005
P. Curtis
This paper reviews some of the work performed on the ground effects rig at BAE Systems in Warton, the now unique facility for modelling dynamic vertical landings and measuring hot gas ingestion. The paper discusses the flow diagnostic tools which have been used in recent times, up to the complexity of 3D PIV, and uses examples from the F-35 JSF programme to illustrate these. The paper hopefully demonstrates the difficulties of using these tools, as well as the benefits they can bring to a development programme.
The ground effects rig is a facility designed to measure temperature rise in aircraft intakes during vertical manoeuvres close to the ground. It is a complex facility that comes as close as possible to accurately modelling the flowfields around an aircraft moving both vertically and horizontally near the ground, with the ability to model dynamic pitch and roll at the same time.
Standard instrumentation for the models consists of rapid response thermocouples mounted in a rake at the engine face. 45 thermocouples of 0·05mm diameter with a time constant of about 10ms are used.
Although, with its standard instrumentation, the rig can measure how much hot gas gets to the engine face, it doesn’t show how it got there, or where it came from, which is the knowledge required to improve the design. Hence there is a need for flow diagnostics.
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Comprehensive validation of an intermittency transport model for transitional low-pressure turbine flows
01/03/2005
Y. B. Suzen and P. G. Huang
A transport equation for the intermittency factor is employed to predict transitional flows under the effects of pressure gradients, freestream turbulence intensities, Reynolds number variations, flow separation and reattachment, and unsteady wake–blade interactions representing diverse operating conditions encountered in low-pressure turbines. The intermittent behaviour of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, mt, with the intermittency factor, g. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The onset location of transition is obtained from correlations based on boundary-layer momentum thickness, accelaration parameter, and turbulence intensity. The intermittency factor is obtained from a transport model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction.
The intermittency transport model is tested and validated against several well documented low pressure turbine experiments ranging from flat plate cases to unsteady wake–blade interaction experiments. Overall, good agreement between the experimental data and computational results is obtained illustrating the predicting capabilities of the model and the current intermittency transport modelling approach for transitional flow simulations.
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Infra-red signature reduction study on a small-scale jet engine
01/02/2005
J. Dix, A.J. Saddington, K. Knowles and M.A. Richardson
This paper presents infra-red signature data for a small-scale, low pressure ratio turbojet engine typical of that used in unmanned air vehicle applications. The aim of the study was to test a number of different convergent nozzle designs concentrating on those with trailing edge modifications. The engine used in the tests has a single stage centrifugal compressor and radial inflow turbine and is designed to produce approximately 150N of thrust at 103,500rpm using liquid propane fuel. The test rig consisted of a calibrated thrust stand whilst the engine was controlled through an electronic engine control unit and laptop PC. The jet plume was visualised using an infra-red spectroradiometer which yielded qualitative data across the infra-red spectrum. Simultaneous measurements were also made of the engine thrust. A Pitot probe was used to take pressure readings across different sections of the exhaust flow. Analysis of the infra-red signature of the engine exhaust plume and any thrust penalty yielded a performance comparison for each of the nozzles tested. Correlation of engine thrust with engine rpm showed that, within the accuracy of the measurements, there was no significant thrust penalty associated with the notched nozzles. Infra-red imagery of the plain and 60° notched nozzles indicated that the latter reduced the length of the hottest part of the exhaust plume by approximately 33%. The spectroradiometer data shows a significant reduction in spectral radiance for the CO2 wavelength of approximately 4·3µm when the notched nozzles are used. The 60° notched nozzle appeared to perform best in reducing the spectral radiance at this wavelength. Centreline total pressure measurements in the exhaust plume correlated well with the infra-red imagery in that a potential core length reduction of up to 30% could be achieved using the 60° notched nozzle. Total pressure contours recorded 20mm (0·43D) downstream of the nozzle exit plane suggest that the notched nozzles are promoting increased mixing through radial spreading of the jet possibly associated with increased streamwise vorticity (although the latter could not be confirmed). There were also signs that the jet plumes being investigated were swirling.
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Life before & after implementation of an acoustic noise reduction enclosure
01/02/2005
B. Timmins
This paper looks back on the designs and ambitions of ARA in resolving a long term acoustic noise problem which threatened ARA with closure. This paper today briefly looks back to the original issues but deals more fully with the later phases of a two phase project implementation and construction. ARA is now a truly ‘silent site’, where closure was once threatened, ARA has achieved the implementation of a bespoke noise reduction enclosure where 24-hour running has proved to be a reality. This paper looks at the design and construction phases, the ‘before and after’ noise footprints and at some of the financial benefits ARA has achieved.
The ARA transonic wind tunnel is sited on an industrial estate on the north west perimeter of Bedford. When it was first built it was on an original farm site with no appreciable residential houses in close proximity. Since the early 1950s there has been considerable residential development around the ARA site resulting in the local householders complaining about the wind tunnel acoustic noise. In early 1999 ARA was obliged to consider several options for noise reduction measures to reduce the noise to within UK government statutory requirements.
This paper deals briefly with the original noise nuisance characteristics and footprint, the noise reduction design and method that ARA selected and shows the construction phases, the further noise treatment ARA had to do on other major ancillary equipment to make ARA a truly quiet industrial site.
The paper shows how ARA has utilised the resulting benefits of these investments to increase productivity and reduce costs, and the influence it has had on ARA’s financial health.
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Industry applications of advanced flow diagnostics-expereience in the BAE systems ground effects rig
01/02/2005
P. Curtis
This paper reviews some of the work performed on the ground effects rig at BAE Systems in Warton, the now unique facility for modelling dynamic vertical landings and measuring hot gas ingestion. The paper discusses the flow diagnostic tools which have been used in recent times, up to the complexity of 3D PIV, and uses examples from the F-35 JSF programme to illustrate these. The paper hopefully demonstrates the difficulties of using these tools, as well as the benefits they can bring to a development programme.
The ground effects rig is a facility designed to measure temperature rise in aircraft intakes during vertical manoeuvres close to the ground. It is a complex facility that comes as close as possible to accurately modelling the flowfields around an aircraft moving both vertically and horizontally near the ground, with the ability to model dynamic pitch and roll at the same time.
Standard instrumentation for the models consists of rapid response thermocouples mounted in a rake at the engine face. 45 thermocouples of 0·05mm diameter with a time constant of about 10ms are used.
Although, with its standard instrumentation, the rig can measure how much hot gas gets to the engine face, it doesn’t show how it got there, or where it came from, which is the knowledge required to improve the design. Hence there is a need for flow diagnostics.
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2D Numerical study of circular synthetic jets in quiescent flow
01/02/2005
H Tang S Zhong
2D numerical simulations of flows generated by a synthetic jet actuator with a circular orifice were conducted at two different diaphragm displacement settings, one representing a typical laminar case and the other a fully turbulent case. The flow in the cavity was included in the computation in order to provide more accurate predictions. A velocity boundary condition was applied at the neutral position of the diaphragm to account for its temporal deformation. Comparisons were made between the computational results and existing PIV and hot-wire data in terms of the time sequence of the velocity vector field, velocity variations in space and with time. It is found that computational results for the laminar case agree well with the experimental data. Four turbulent models were tested for the fully turbulent case. It was found that the predictions using the RNG k-e and Standard k-e models were reasonably close to the experimental data. This initial study has produced some encouraging evidence for the capacity of FLUENT in simulating the key features of synthetic jets.
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Experimental investigation of the effect of nozzle shape & test section perforation & stationary characteristics of flow field in the large transonic TsAGI T-128 wind tunnel
01/02/2005
V.I. Biryukov, S.A. Glazkov, A.R. Gorbushin, A.I. Ivanov, A.V. Semenov
The results are presented for a cycle of experimental investigations of flow field characteristics (static pressure distribution, static pressure fluctuations, upwash, boundary layer parameters) in the perforated test section of the transonic TsAGI T-128 wind tunnel. The investigations concern the effect of nozzle shape, wall open-area ratio, Mach and Reynolds numbers on the above-outlined flow characteristics. During the tests, the main wind tunnel drive power is measured. Optimal parameters of the nozzle shape and test section perforation are obtained to minimize acoustic perturbations in the test section and their non-uniformity in frequency, static pressure field non-uniformity, nozzle and test section drag and, accordingly, required main wind tunnel drive power.
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Evaluation of CFD methods for transport aircraft high lift systems
01/02/2005
R Rudnik, P Eilasson and J Perraud
Major results and findings of the numerical work package of the European high lift programme EUROLIFT are outlined. The main objective of these studies is to validate and test numerical methods for the prediction of high lift flows for transport aircraft configurations. The activities comprise the assessment of current CFD methods for 3D flows, evaluation of means for code improvement, and transition prediction. All aspects are especially devoted to high lift flow problems. A general capability to predict maximum lift on a simplified wing/fuselage high lift configuration is demonstrated by a variety of different numerical approaches. In general, major shortcomings are the reliability and the accurate simulation of large separation areas and the turn-around time to compute 3D lift polars. Advanced turbulence modelling and numerical solver features, such as the preconditioning technique, show a potential to overcome these deficiencies. Promising results with respect to transition prediction were obtained on a swept high lift wing using a database method. The results obtained in the numerical activities represent major ingredients on the way to a consistent numerical approach for the simulation of transport aircraft high lift configurations including all maximum lift determining effects.
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Investigation into Clustering of Synthetic Jet Actuators
01/01/2005
S. C. Liddle and N. J. Wood
An investigation into the behaviour of clustered synthetic jet Actuators for flow-control applications is described. Experiments have been undertaken with two small-scale synthetic jet actuators in a zero-pressure gradient boundary-layer, in order to investigate the effect of configuration yaw angle and relative input signal phase. Oil-flow visualisation and hotwire anemometry techniques were used, demonstrating that changes in the downstream flow structure could be observed. Compared to a streamwise configuration, in which a symmetrical counter-rotating vortex pair was produced by the synthetic jet-boundary-layer interaction, a broader asymmetric interaction was produced in a 15° yaw configuration. Streamwise velocity contour plots, illustrating the development of the interaction downstream, over four phase angles, were presented. Significant differences in the PSD analyses of downstream streamwise velocity time histories were found, suggesting that input signal phase could influence the stability and hence effectiveness of flow structures used in flow-control applications.
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The vortex merger factor in aircraft wake turbulence
01/01/2005
M. Mokry
Vortex merger is studied within the context of two-dimensional discrete vortex sheets and demonstrated on two equally oriented circular vortices and aircraft tip and flap vortices. It is confirmed that, depending on the wing load distribution, the latter may or may not coalesce into a single counter-rotating pair. The interaction of a vortex with an equally oriented shear layer, governed by the same physical principle, suggests a possible intensification of an aircraft vortex in cross-wind shear.
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Flight control system damage simulation using freely flying models
01/01/2005
S Sadovnychiy, A Ryzhenko and A Bentin
This article deals with a damage simulation of flight control systems during a flight. As a subject of flight tests the model of a classic aerodynamic aircraft scheme is considered. This aircraft has highly swept wings a moderate wing elongation and all-moving horizontal tail surfaces. The diagrams of flight parameters from flight tests of the freely flying models with loss of a control surface in flight are given. The investigation results for the failures leading to a sharp drop in the stiffness of the control units in the pitch channel are given. The damage investigation in horizontal flight and in complex manoeuvres is given.
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Intergrated design of flight simulator motion cueing systems
01/01/2005
Rudd Hosman Sunjoo Advani and Nils Haeck
An advanced design process applicable to the specification of flight simulator cueing systems is presented in this paper. This process is based on the analysis of the pilot-vehicle control loop by using a pilot model incorporating both visual and vestibular feedback, and the aircraft dynamics. After substituting the model for the simulated aircraft, the analysis tools are used to adjust the washout filter parameters with the goal of restoring pilot control behaviour. This process allows the specification of the motion cueing algorithm. Then, based on flight files representative of the operational flight envelope, the required motion system space is determined. The motion-base geometry is established based on practical limitations, as well as criteria for the stability of the platform with respect to singular conditions. With this process the characteristics of the aircraft, the tasks to be simulated, and the missions themselves are taken into account in defining the simulator motion cueing system.
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Vortex flows on UAVs: Issues and challenges
01/12/2004
I. Gursul
Separated and vortical flows are dominant over various unmanned
air vehicles (UAVs). In this article, issues and challenges of
vortical flows for future UAVs are reviewed. These include shear
layer instabilities, vortex breakdown and wing stall, vortex
interactions, nonslender vortices, multiple vortices, and
manoeuvring wing vortices. There are also issues relating to
vortical flows in certain flow/structure interactions, as well as in
aerodynamics/propulsion interactions. Separated and vortical
flows are even more dominant at low Reynolds number flows. The
main features of vortical flows, unsteady aerodynamics, and
propulsion related vortical flow isssues relevant to mini- and
micro air vehicles, are discussed.
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Application of generic algorithms in aerodynamic optimisation design procedures
01/12/2004
R. P. Clayton and R. F. Martinez-Botas
Direct optimisation techniques using different methods are presented
and compared for the solution of two common flows: a two dimensional
diffuser and a drag minimisation problem of a fixed area
body. The methods studied are a truncated Newton algorithm
(gradient method), a simplex approach (direct search method) and a
genetic algorithm (stochastic method). The diffuser problem has a
known solution supported by experimental data, it has one design
performance measure (the pressure coefficient) and two design variables.
The fixed area body also has one performance measure (the
drag coefficient), but this time there are four design variables; no
experimental data is available, this computation is performed to
assess the speed/progression of solution.
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Enhancement of thrust reverser cascade performance using aerodynamic structural integration
01/12/2004
J. Butterfield, H. Yao, M. Price, C. Armstrong, S. Raghunathan, E. Benard, R. Cooper and D. Monaghan
This paper focuses on the design of a cascade within a cold stream
thrust reverser during the early, conceptual stage of the product
development process. A reliable procedure is developed for the
exchange of geometric and load data between a two dimensional
aerodynamic model and a three dimensional structural model.
Aerodynamic and structural simulations are carried out using
realistic operating conditions, for three different design configurations
with a view to minimising weight for equivalent or improved
aerodynamic and structural performance. For normal operational
conditions the simulations show that total reverse thrust is
unaffected when the performance of the deformed vanes is
compared to the un-deformed case. This shows that for the conditions
tested, the minimal deformation of the cascade vanes has no
significant affect on aerodynamic efficiency and that there is scope
for reducing the weight of the cascade.
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Achieving drag measurement accuracy from a high load capacity internal balance design
01/12/2004
R Porter
As one aspect of a balance research and development programme,
engineers at the Aircraft Research Association (ARA) have
addressed the unique problems associated with the design of an
internal single piece balance suitable for small military type
aircraft models that experience very high loads during a wind
tunnel test. The paper details the nature of the problems and the
stages undertaken in the design, manufacture and commissioning
of an initial prototype balance followed by a re-designed version
to meet the stringent requirements. Data from recent tests indicate
the quality of the measurements and the suitability of the balance
for the testing of fighter type aircraft.
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Design criteria for conceptual sizing of primary flight controls
01/12/2004
A J Steer
The European Supersonic Commercial Transport’s control surface
configuration is based largely on Concorde’s and has been scaled to
provide comparable un-augmented stability and manoeuvre performance.
Hence, optimising the surface size could provide significant
performance benefits in terms of reduced drag, noise, structural and
actuator power requirements. Adequate control power will be
required to meet current civil aviation regulations whose primary
aim is to ensure the aircraft can be flown safely during both normal
and emergency operation. Additional design criteria, combined with
the optimum longitudinal control laws, are required to ensure desirable
handling qualities with minimum pilot workload.
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Effect of counter-rotating vortices on the development of aircraft wakes
01/11/2004
A Panaras and S G Voutsinas
A two-dimensional vortex particle model is used for studying the
development of the vortex wake generated by the wing of an aircraft
in the Trefftz plane. Two-dimensional, finite-area vortex structures
simulate the initial vorticity distribution at a near-field cross-section
of the wing, as provided by either measurements or simulations. The
code is used for studying the effect of weak or strong counterrotating
vortices on the development of an aircraft wake. Application
in a three-vortex configuration, consisting of the tip and flap
vortices, plus a weak negative vorticity sheet lying between them,
supports the hypothesis of Graham(25) that the merging of the tip and
flap vortices is prevented, because in such an arrangement the
counter-rotating vorticity sheet is wrapped around the primary
vortices.
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The Fairey Rotodyne - technology before its time?
01/11/2004
D Gibbings
THE LEGACY OF JUAN DE LA CIERVA
It cannot have escaped notice, that in two months time we will celebrate
the centenary of the first flight of a powered aircraft carrying a
man. We rightfully acclaim ‘The miracle at Kitty Hawk’ for all that
it has meant to our chosen profession, albeit outside our remit as a
rotorcraft section.
There is however a significant 80th anniversary, which we can
add to this centenary year. On 9 January 1923, a Cierva C-4 autogyro
piloted by Lt Alejandro Gomez Spencer made an officially
observed circular flight of over 4km (2⋅5 miles) in Madrid.
This important event brought the name of Juan de la Cierva to the
fore on the International scene, and was subsequently to prove to be
the key to the modern helicopter, an interesting lesson in technology
in that, Cierva never set out to invent the helicopter, and never
produced one himself.
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Effects of hydrogen-air non-equilibrium chemistry on the performance of a model scramjet thrust nozzle
01/11/2004
R. J. Stalker, N. K. Truong, R. G. Morgan and A. Paull
Two aspects of hydrogen-air non-equilibrium chemistry related to
scramjets are nozzle freezing and a process called ‘kinetic afterburning’
which involves continuation of combustion after expansion
in the nozzle. These effects were investigated numerically and experimentally
with a model scramjet combustion chamber and thrust
nozzle combination. The overall model length was 0⋅5m, while
precombustion Mach numbers of 3⋅1±0⋅3 and precombustion
temperatures ranging from 740K to 1,400K were involved. Nozzle
freezing was investigated at precombustion pressures of 190kPa and
higher, and it was found that the nozzle thrusts were within 6% of
values obtained from finite rate numerical calculations, which were
within 7% of equilibrium calculations. When precombustion pressures
of 70kPa or less were used, kinetic afterburning was found to
be partly responsible for thrust production, in both the numerical
calculations and the experiments.
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Vortex flows on UAVs: Issues and challenges
01/10/2004
I. Gursul
Separated and vortical flows are dominant over various unmanned
air vehicles (UAVs). In this article, issues and challenges of
vortical flows for future UAVs are reviewed. These include shear
layer instabilities, vortex breakdown and wing stall, vortex
interactions, nonslender vortices, multiple vortices, and
manoeuvring wing vortices. There are also issues relating to
vortical flows in certain flow/structure interactions, as well as in
aerodynamics/propulsion interactions. Separated and vortical
flows are even more dominant at low Reynolds number flows. The
main features of vortical flows, unsteady aerodynamics, and
propulsion related vortical flow isssues relevant to mini- and
micro air vehicles, are discussed.
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A question of survival – military aircraft vs the electromagnetic environment
01/09/2004
M Pywell
Military aircraft, by definition, need to survive the onslaught of opposing
forces to successfully complete their mission. From an aircraft perspective,
the electromagnetic (EM) environment can be an enabler, via
the use of navigation aids, radar, radio communications etc. – in fact
mission success depends on its successful use. However, this environment
is also potentially a disabler, as threat weapon systems and the
environment itself can harm or destroy the aircraft. This paper discusses
risks and hazards thus posed to aircraft survivability, partitioned
into two classes – ‘direct’ and ‘indirect’ EM threats. ‘Direct’
threats are those that occur as a result of direct coupling of EM energy
to the airframe and systems within, e.g. lightning strike and directed
energy weapons. ‘Indirect’ threats are those that utilise EM sensors to
detect, track and target the aircraft, e.g. radar-guided surface-to-air
missiles.
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Investigation of active control of swept shock wave turbulent boundary-layer interactions - PSP results
01/09/2004
J. S. Couldrick, S. L. Gai, J. F. Milthorpe and K. Shankar
An investigation of active control of the swept shock
wave/boundary-layer interaction using ‘smart’ flap actuators is
presented. The actuators are manufactured by bonding piezoelectric
material to an inert substrate to control the bleed/suction rate
through a plenum chamber. The cavity provides communication of
signals across the shock, allowing rapid thickening of the boundary
layer approaching the shock. This splits the shock foot into a series
of weaker shocks forming a lambda structure, thus reducing wave
drag. Active control allows optimisation of the unimorph deflection,
hence rate of mass transfer.
In this paper, results of the interaction using pressure sensitive
paint (PSP) are emphasised. It is shown that the use of PSP, in
conjunction with discrete pressure data, enables the main features
of the interaction to be observed when the actuators are subject to
different deflections.
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Design methodology and performance of an indraft wind tunnel
01/09/2004
G Johl, M Passmore and P Render
The design methodology and performance of Loughborough University’s
new 1·9m × 1·3m, indraft wind tunnel is discussed in the following
paper. To overcome severe spatial and financial constraints, a
novel configuration was employed, with the inlet and exit placed
adjacent to each other and opened to atmosphere. Using a fine filter
mesh, honeycomb, two turbulence reduction screens and a contraction
ratio of 7·3, flow uniformity in the working area of the jet at
40ms-1 is shown to be within 0·3% deviation from the mean velocity,
with turbulence intensity in the region of 0·15%.
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Vortex breakdown location over 65deg delta wings empiricism and experiment
01/09/2004
CE Jobe
Thirty-eight data sets from static tests of various 65° delta wings in
many water and wind tunnels are compared with four empirical
vortex breakdown location prediction methods and the results of two
Navier-Stokes computations to assess their range of validity in pitch.
Vortex breakdown is the sudden expansion and subsequent chaotic
evolution of the otherwise orderly, spiraling, leading-edge vortex
flow over the upper surface. Large fluctuations occur in vortex
breakdown location at static test conditions making accurate experimental
determination difficult.
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Control of trailing edge separation by tangential blowing inside the bubble
01/08/2004
P R Viswanath and K T Madhavan
Experiments have been performed investigating the effectiveness of
steady tangential blowing, with the blowing slot located downstream
of separation (but inside the separation bubble) to control a trailingedge
separated flow at low speeds. Trailing-edge separation was
induced on a two-dimensional aerofoil-like body and the shear layer
closure occurred in the near-wake. Measurements made consisted of
model surface pressures and mean velocity, turbulent shear stress
and kinetic energy profiles in the separated zone using a two-component
LDV system. It is explicitly demonstrated that the novel
concept of tangential blowing inside the bubble can be an effective
means of control for trailing-edge separated flows as well. Blowing
mass and momentum requirements for the suppression of wall and
wake flow reversals have been estimated.
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A structure coupled CFD method for time-marching flutter analysis
01/08/2004
N V Taylor, C B Allen, A Gaitonde and D P Jones
Aeroelastic analysis is a critical area of the aircraft design process, as
a good understanding of the dynamic behaviour of the wing structure
is essential to safe operation of the vehicle. The inevitable inaccuracies
present in the modelling of such phenomena impose mass penalties,
as large safety margins are necessitated, which in turn lead to
overly stiff designs. In an effort to reduce the uncertainty in analysis
methods, fully coupled CFD and structural models are under widespread
development. This paper describes the results produced by
such a system for a series of test cases based on the AGARD445.6
and MDO wings. Results relating to the latter are of particular
interest, as significant variations were found to be produced by the
different methodologies used in previous studies, the precise cause
of which could not be isolated.
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Aeroelastically adaptive propeller using blades root flexibility
01/08/2004
Y Sandek and A Rosen
Usually a fixed pitch propeller is designed to be optimal at cruise
speeds. Thus the efficiency is quite low at takeoff or low speeds, as
well as during other flight regimes. The present paper shows that by
introducing a flexible element into the blade root, the propeller efficiency
can be improved over a wide range of velocities. The flexible
element reacts to root flap or torsion moments by changing the blade
pitch at the root. The root flexibility and the pitch angles at the root at
zero loads are chosen such that efficiency will increase during problematic
regimes without decreasing the propeller thrust. In the case of
straight blades the torsional moment at the root is too small to be used.
In the case of swept blades this moment component is significantly increased
and can contribute to the design of an optimal aeroelastically
adaptive propeller.
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Flow visualisation experiments for turbine film cooling
01/08/2004
C A Coat and G D Lock
Flow visualisation experiments related to turbine film cooling have
been conducted. These investigated the fluid mechanics of coolant
ejection using a large-scale, flat-plate model at engine-representative
Reynolds numbers in a low-speed tunnel with ambient-temperature
mainstream flow. The coolant trajectories were captured using a fine
nylon mesh covered with thermochromic liquid crystals, allowing
measurement of gas temperature contours in planes perpendicular to
the flow.
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Experimental and numerical aerodynamic analysis of a satellite launch vehicle eith strap-on boosters
01/07/2004
A Naghib-Lahouti, M Mani and M Nazarinia
Results of numerical simulation of inviscid compressible flow
around a generic satellite launch vehicle (SLV) with strap-on boosters
using a commercial computational fluid dynamics (CFD) code
named Star-CD are experimentally evaluated. Governing equations
of flow around the SLV with two and two strap-on boosters were
solved in three dimensions using the SIMPLE algorithm in an
unstructured tetrahedral mesh, to determine longitudinal aerodynamic
coefficients and surface pressure distribution at Mach numbers from
0·6 to 2·0, and angles-of-attack from 0° to 16°. To evaluate the
numerical results, 1:100th scale models of the SLV were tested in a
trisonic wind tunnel in the same configurations and flow conditions
as those analysed numerically. Comparison of results shows reasonable
agreement between numerical and experimental values,
however, drag coefficients had to be corrected to compensate the effects
of base flow and the struts connecting the boosters to the core
rocket.
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Dynamic modelling and stability of hingeless helicopter blades with a smart spring
01/07/2004
F F Afagh, F Nitzche and N Morozova
The aeroelastic stability of a uniform, untwisted hingeless ‘smart’
helicopter rotor blade in hover has been analysed. The concept of a
‘smart’ blade is achieved by implementing a piezoelectric stack at an
appropriate location along a host blade such that upon actuation it
enters the load path becoming an integral part of the host structure.
Thus, the stiffness characteristics of the rotor are altered causing
modal damping augmentation of the blade. The perturbation equations
of motion for the ‘smart’ blade that describe the unsteady blade
motion about the equilibrium operating condition are obtained using
Galerkin’s method. These differential equations with periodic time
coefficients are analysed for stability utilising the Floquet method.
Six different regimes of actuation are investigated, and a parametric
study is carried out by considering six different design cases.
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Unsteady aerodynamic model of a cargo container for slung-load simulation
01/07/2004
L S Cicolani, J G A da Silva, E P N Duque and M B Tischler
The problem of simulation models capable of predicting the aerodynamic
instability of helicopter slung-load cargo containers and bluff
bodies is addressed. Instability for these loads is known to depend on
unsteady frequency-dependent aerodynamics, but simulation models
that include the unsteady aerodynamics do not currently exist. This
paper presents a method for generating such models using computational
fluid dynamics (CFD) to generate forced-oscillation aerodynamic
data and frequency domain system identification techniques to
generate a frequency response from the CFD data and to identify a
transfer function fit to the frequency response. The method is independent
of the responsible flow phenomenon and is expected to apply
to bluff-bodies generally. Preliminary results are presented for the case
of the 6- by 6- by 8-ft CONEX (container express) cargo container.
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State-space inflow modelling for lifting rotors with mass injection
01/07/2004
K Yu and D A Peters
In the field of rotorcraft dynamics, it is significant that the induced
inflow field is well understood and modeled. A large number of
methodologies have been developed in the past years, among which
the state-space model is recognised for its advantage in real-time
simulation, preliminary design, and dynamic eigenvalue analysis.
Recent studies have shown success in representing the induced flow
field everywhere above the rotor plane even with mass source terms
on the disk as long as they have zero net flux of mass injection when
integrated over the disk. Nevertheless, non-zero net mass influx is
expected in numerous situations, such as ground effect, tip drive
rotors, etc; and the incapability of previous models limits the utilisation
of the methodology in these cases.
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Supersonic transport aircraft longitudinal flight control law design
01/06/2004
A J Steer
Modern civil transport aircraft utilise increasingly complex
command and stability augmentation systems to restore stability,
optimise aerodynamic performance and provide the pilot with the
optimum handling qualities. Provided it has sufficient control power
a second generation fly-by-wire supersonic transport aircraft should
be capable of exhibiting similarly desirable low-speed handling
qualities. However, successful flight control law design requires
identification of the ideal command response type for a particular
phase of flight, a set of valid handling quality design criteria and
piloted simulation evaluation tasks and metrics. A non-linear mathematical
model of the European supersonic transport aircraft has been
synthesized on the final approach to land. Specific handling quality
design criteria have been proposed to enable the non-linear dynamic
inversion flight control laws to be designed, with piloted simulation
used for validation.
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A novel method for the provision of flight experience and flight testing for undergraduate aeronautical engineers at the University of Strathclyde
01/06/2004
M T Strickland & T J Scanlon
The Department of Mechanical Engineering at the University of
Strathclyde has developed a novel flight experience/test course for
undergraduate Aeronautical Engineers. In common with similar
courses at undergraduate level the course contains practical instruction
in how an aircraft is flown, an analysis of its stall characteristics
and an assessment of an aircraft’s performance and stability. However,
uniquely, the Strathclyde course consists of dual instructional flights
in two seat gliders. This paper contains a detailed description of the
flight experience/test course developed at Strathclyde and its incorporation
into the undergraduate curriculum. A critical analysis of its
delivery is also presented.
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Aerodynamic forces and moments on an ogive cylinder at incidence
01/06/2004
S C Luo, Y T Ng & T T Lim
In flows over an ogive cylinder placed at incidence, it is well documented
that a side force acts on the cylinder. However, little is
known about the relation between the side force (CFy) and other
force and moment components. In this note, the variations of three
force and three moment components, acting on the ogive cylinder,
with roll angle are measured simultaneously. The model was placed
at four different angles-of-attack, namely á = 30°, 45°, 50° and 60°
and the results show that in addition to CFy, the variation of CFz, CMx,
and CMz with the roll angle also exhibit the square wave like behaviour
at á = 45° and 50°, and with the same cross over ö positions,
while CFx and CMy remain relatively constant irrespective of the roll
angle. The magnitudes of CFx and CMy were found to increase with
angle of attack and were thought to be due to the increase in normal
frontal area.
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On wake vortex response for all combinations of five classes of aircraft
01/06/2004
L M B C Campos & J M G Marques
The present paper concerns the response of a following airplane to a
pair of wing tip vortices left by a leading aircraft, represented by the
Hallock-Burnham model, including the effect of vorticity decay
between the two aircraft. The effect of vorticity is evaluated in terms
of the induced rolling moment and also the lift loss; these specify the
roll acceleration and the downward acceleration, respectively. The
corresponding two response equations can be put into the same
dimensionless form, and integrated using exponential integrals. This
specifies the roll rate and sink rate as a function of time; besides the
latter, the bank angle and altitude loss, are also plotted, all also as a
function of time, for all combinations of leading and following
aircraft in five classes.
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Notched strength estimations of graphite epoxy composite laminates containing central holes and cracks: A statistical approach
01/05/2004
P K G Potti, B N Rao & V K Srivastava
A statistical approach is followed for prediction of tolerences of
notched strength of composite laminates using the recently proposed
improved inherent flaw model (IFM). In order to examine the
validity of this approach, the existing fracture data on graphite/epoxy
composite laminates containing central holes and cracks were used.
The notched strength estimations are found to be within the range of
tested values.
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Multigrid multiblock hovering rotor solutions
01/05/2004
C B Allen
The effect of multigrid acceleration implemented within an upwind-
biased Euler method for hovering rotor flows is presented.
Previous work has considered multigrid convergence for structured
single block rotor solutions. However, for forward flight
simulation a multiblock approach is essential and, hence, the flowsolver
has been extended to include multigrid acceleration within
a multiblock solver. The requirement to capture the vortical wake
development over several turns means a long numerical integration
time is required for hovering rotors, and the solution (wake)
away from the blade is significant. Hence, the solution evolution
and convergence is different to a fixed wing case where convergence
depends primarily on propagating errors away from the surface
as quickly as possible, and multigrid acceleration is shown
here to be less effective for hovering rotor flows.
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Derivation of control activity metrics for the rule-based prediction of helicopterpilot workload
01/05/2004
C A Macdonald & R Bradley
Control activity is a recognised gauge of pilot workload and recent
research has employed wavelet decomposition to classify discrete
control actions into categories such as guidance and stabilisation.
The aim of the present work is to extend the wavelet approach so
that workload may be quantified through sets of rules based on
appropriate control activity metrics. The rules are derived from
data collected in piloted simulation trials of a variety of flying
tasks involving a number of pilots and different helicopter configurations.
Statistical tests are then applied which test the efficacy of
the derived rules. The immediate aim of the research is to establish
whether workload can be successfully predicted from control
responses. The underlying goal however, is to be able to predict
workload ratings from desktop simulations in order to provide
indicative workload information at the design stage. The contribution
of the current study to this objective is discussed.
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Airspace safety in New Zealand: A Causal analysis of controller caused airspace incidents between 1994 - 2002
01/05/2004
A Maajumder & P Nalder
The New Zealand Government takes airspace safety very seriously.
The level of safety in New Zealand airspace is measured by the
number of recorded airspace incidents. An airspace incident can be
thought of as a failure in the chain of operations in the air traffic
system when it is provided with an air traffic service (ATS). Some of
these incidents result in a loss of separation between aircraft, varying
from slight to a very serious loss with a significant risk of collision,
known as a near collision. New Zealand’s Civil Aviation Authority
(CAA) identifies the causal factors for all airspace incidents using
the Reason model of human error, divided into three areas; active
failures committed by individuals involved in the incident, local
factors relating to the task and the ATS environment and organisational
factors originating in the managerial and organisation spheres
of the ATS provider.
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Fuel sensitivity analyses for active drag reduction systems
01/04/2004
T M Young
Active drag reduction systems, such as hybrid laminar flow control
(HLFC), have the potential for significant fuel savings; however, this
is at the expense of an increase in aircraft weight and engine power
off-take. A computer program – capable of accurately determining
the trip fuel for a given mission profile – has been developed. The
program was validated against manufacturer’s payload-range data,
and then modified to emulate the installation of an active drag reduction
system, by incorporating changes to the drag polars, specific
fuel consumption (SFC) data and operating empty weight (OEW).
Results of sensitivity studies are presented that enable the reduction
in trip fuel to be determined for given changes in CD, SFC and
OEW. The underlying assumption of linear independence of the
three parameters is explored.
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Robotic in-orbit servicers - the need for control moment gyroscopes for attitude control
01/04/2004
A Ellery
Robotic in-orbit servicing has yet to be realised due to a number of
technical difficulties. One such difficulty is analysed here. The
requirement for force control in robotic manipulation imposes significant
design requirements on space robots by virtue of the lack of a
mounting platform to react against external forces and torques. The
spacecraft attitude control system must effectively serve the same
role as the ground in terrestrial manipulators. The reaction torques
imposed on the spacecraft due to the manipulators is high when
force control is used in grappling targets in space, limiting the choice
of attititude actuator to control moment gyroscopes.
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Analysis of anisotropic prismatic sections
01/04/2004
G F J Hill & P M Weaver
The dynamic behaviour of rotor blades is often modelled using onedimensional
beam analysis with equivalent mass and stiffness properties
to those of the full blade. Calculation of accurate elastic
stiffness terms for these arbitrarily shaped sections with differing
material properties is vital to this process. A method which produces
these properties using standar
