They seem to be so small and unstable, thinking about the weight of the airplane, especially filled with passangers and luggage. How do they carry the weight, as well as being able to accelerate and break and everything?
In: 1057
The wheels don’t do any acceleration so that is not an issue. They just need to roll and break after landing. The wheels themselves are very heavy duty and usually come in pairs (or even more). They are changed quite often because they lose some rubber every time the plane lands. You can see the black skid marks they leave behind on runways. The brakes aren’t fundamentally that different but they too have to be quite heavy duty and fault tolerant.
Now for the real question of why it makes sense for the wheels to be small. Larger wheels would have a higher moment of inertia. That would make them drag a lot more when landing until they get match the speed of the aircraft. Smaller wheels have a smaller moment of inertia so they match the speed sooner. Some planes have relatively large wheels. They are needed to be able to land in the wilderness or outside paved runways at least. They also come in rather slow, so it doesn’t take much for the wheels to match speed when landing.
The wheels don’t do any acceleration so that is not an issue. They just need to roll and break after landing. The wheels themselves are very heavy duty and usually come in pairs (or even more). They are changed quite often because they lose some rubber every time the plane lands. You can see the black skid marks they leave behind on runways. The brakes aren’t fundamentally that different but they too have to be quite heavy duty and fault tolerant.
Now for the real question of why it makes sense for the wheels to be small. Larger wheels would have a higher moment of inertia. That would make them drag a lot more when landing until they get match the speed of the aircraft. Smaller wheels have a smaller moment of inertia so they match the speed sooner. Some planes have relatively large wheels. They are needed to be able to land in the wilderness or outside paved runways at least. They also come in rather slow, so it doesn’t take much for the wheels to match speed when landing.
Unlike a car tire they don’t need to be engineered for much traction, uneven terrain, or a comfterable ride. They need to roll a few thousand feet at a time in a straight line down what is usually a very well maintained stretch of asphalt. They mostly just need to carry weight and withstand the varying temperature and preasure conditions as the aircraft changes altitude.
Unlike a car tire they don’t need to be engineered for much traction, uneven terrain, or a comfterable ride. They need to roll a few thousand feet at a time in a straight line down what is usually a very well maintained stretch of asphalt. They mostly just need to carry weight and withstand the varying temperature and preasure conditions as the aircraft changes altitude.
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Planes are light relative to their size. For example an average passenger plane like an Airbus A321 weighs less than a battle tank. They’re designed to be as light as possible for their size because that enables them to carry heavy loads. Their wheels may appear small relative to the rest of the plane but they’re probably the hardiest parts of the whole aircraft. They can take the repeated abuse of take off and landing which produce immense forces. They use hydraulic shock absorbers much like cars but they’re turned up to 11. They’re very thick, very sturdy, and their tires are rated for extreme loads.
They may look small but they’re not.
Planes are light relative to their size. For example an average passenger plane like an Airbus A321 weighs less than a battle tank. They’re designed to be as light as possible for their size because that enables them to carry heavy loads. Their wheels may appear small relative to the rest of the plane but they’re probably the hardiest parts of the whole aircraft. They can take the repeated abuse of take off and landing which produce immense forces. They use hydraulic shock absorbers much like cars but they’re turned up to 11. They’re very thick, very sturdy, and their tires are rated for extreme loads.
They may look small but they’re not.
They must carry the weight. They do not need to be able to accelerate; the engines push air. Braking is a “nice-to-have.” Cornering ability at anything much above walking speed only needs to be sufficient to navigate the turns on a, um, runway.
So the main requirements are:
– holds the weight of the airplane
– withstands spinning at full takeoff speed
– has *some* traction
That’s basically it. The main question here is about weight.
It’s not actually the tires that hold the weight. It’s the air inside the tires. The tires simply hold that air in place.
Let’s say you have a plane that weighs 200,000 pounds. A 757, say. If your tires are inflated to 200 psi you’ll need a total “contact patch” of 1000 square inches between all the tires. That sounds like a lot but there are ten tires. Each one needs 100 sq in or about a ten inch square of contact patch, at high air pressure, to hold that weight. That’s pretty doable.
You want the smallest and lightest tires that can hold enough pressure to support the weight. Rather than going with monster tires, you generally add more tires. (A little Cessna has 3 tires; a 737 has six; a big 747 has eighteen tires.) The goals being, the tires need to be compact enough to stow inside the plane and light enough to carry, yet strong enough to land on. The best tire for the job is not the biggest!
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