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336 articles found.
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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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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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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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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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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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, inc
