Most of us spend quite a bit of time wondering how aircraft get off the ground and into the air. But what about getting back down again? Think of the great weight of an aircraft full of passengers and their luggage. Think about the speed that the aircraft is doing when it eventually settles down on to the ground.
Words like 'heavy' and 'fast' come to mind. Very heavy and very fast!
Think about an aircraft landing. Which part of the aircraft touches down on the ground first? Wing, Tail, Wheel, Nose, Tyre ?
Trick question! Yes, the tyre is part of the wheel and it is the first part of the aircraft to touch the ground.
The wheel is connected to a strut and that is attached to the aircraft fuselage. Together these three parts make up the landing gear of an aircraft.
| If you look at this picture of landing gear you can see that it has a basic framework: wheel, strut and tyre. | |
| It's obvious to you and me that this landing gear has to be perfect. The lives of every passenger and every crew member depend on it.
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So, what exactly does each of the three main parts of the landing gear have to be able to do?
Yes, I think you should consider a career in aeronautics. Who knows - you might end up designing the first aircraft to journey across the surface of Mars? Less gravity than earth and what would you use to build it? Now there's a project for you!
Back to our landing gear - you'll still need these on Mars anyway. Won’t you?
When you look back over these ideas so far, you can tell that building landing gear has a lot to do with two ideas: choosing the right materials and designing the right shapes of the structures themselves.
Aircraft companies buy their materials from other companies - there are specialist companies who make aircraft tyres and wheels. There are companies who produce the materials used in the struts, wheels and tyres.
These specialist companies spend huge amounts of money testing and developing new materials. Each material must be able to do its job. In the other activities you were picking out some characteristics, or properties of the different materials.
Try this quiz to see what properties are need for the different materials that make up the landing gear.
Now, which material would best suit each of the parts? Metal? Rubber? Plastic?
Yes, you probably thought that metal would be right for the strut and for the wheel, and that rubber would be good material for a tyre. In the early days, these were the choices made. Today we use a mix of metals, called an alloy. Rubber from trees is expensive today, and it is not always strong enough. So people have added other substances to the rubber.
Some metals like aluminium are strong, stiff and light and are used to make wings. Steel is another alloy. It is strong enough for landing gear. Even a small piece of steel is very strong.
| Look at the landing gear again. It swings up into the aircraft during flight so it has to be compact too. Just look at the number of parts. They're all different shapes and sizes and they fit together perfectly. It's not enough to have the right material: it also has to be the right shape for the job. Designing the shapes is a major part of making an aircraft. Look at the strut that connects the fuselage to the wheels. And look how it is joined to the wheel system and to the fuselage. Is there only one joining place for each? Why so many joins? |
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Look at this table; you might even have one like it. Look at how the single leg is joined to the tabletop, and how it stands on the floor. Now try this. Balance a book on top of the end of your pencil. You're right
- it can't be done. It won't balance. |
Now take another look at our landing gear. Look for a similar pattern of joins to share the load. And what a load - all those passengers and luggage, never mind the weight of the aircraft itself! All the enormous pushes are spread out because the designer has shaped the landing gear to do this job properly and safely.
Did you know that when an aircraft is being designed, the landing gear is one of the first parts to be decided upon? Manufacturers talk over with their customers - the airlines - the numbers of passengers and where the aircraft will need to fly. They look at the runways it will land on and work out how many wheels will be needed to land the aircraft safely. Then they decide how big the landing gear will have to be and finally they decide how big a space will be needed in the fuselage to hold it during flight.
It's a bit like working backwards isn't it?
Have you noticed how many things there are to think about and discuss before you make any decisions about what to build?
Next time you watch an aircraft take off or land, watch the landing gear. And if you take a flight somewhere on holiday, listen for the noises as the landing gear is retracted after take-off and lowered just before landing. Now you know what's happening and why!
Here's another thought - why doesn't the landing gear stay lowered during the whole flight?
ProjectYou need a giant piece of paper and a whole collection of cardboard boxes, tubes and flat sheets. Construct your own landing gear. Try a variety of structures and joins and see if you can support the weight of a couple of books When that's complete, draw your design - you can use paper, paint or a computer art package - whatever you think works best for your idea. And when that's complete you can begin work on the very first aircraft to fly on Mars! The planet which, you will remember, has a different atmosphere from earth, has less gravity than we do on earth. There are two polar ice caps and some enormous canyons, several huge volcanoes (not active - we think, but your aircraft could take a team to find out) and vast areas of boulders and ground covered in fine sand in a million shades of red and brown and rust Enjoy! |
Text courtesy of The Flight Experience, Sponsored by Bombardier Aerospace.