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?
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One important thing about airplane wheels: they do not move the plane. Their only job is to allow the plane to roll, which removes much of the delicate parts that a car wheel (as an example) would have. They are more like the casters on a cabinet or table in that regard instead of the wheels of a land vehicle.
Instead, a plane is moved either by their engine (the same thing that lets them move forward in air, just lower powered until they are taking off) or an extra car that pushes/pulls them along.
Best ELI5 I can think of is they are small compared to the size of the plane, just like a fully loaded shopping cart has tiny wheels too. They do the exact same job, just roll, not much else.
Also, the amount of engineering and processing that goes into airplane suspension and wheels compared to cars would make your head spin.
Airplane wheels are huge and they have a lot of them. The look small compared to the size of the airplane. Airplane are compared to the volume lighter then cars or trucks.
Here is a human sitting on the wheels of a Boeing 747 [https://qph.cf2.quoracdn.net/main-qimg-9f2d76bc87612ad7b70333439ddac6e0-lq](https://qph.cf2.quoracdn.net/main-qimg-9f2d76bc87612ad7b70333439ddac6e0-lq) The tire is 49 inch in outer diameter and have 19 inch thread area.
A typical car has 15-19 inch diameter and an area around 9 inches wide. So a 747 tire is 2x as wide and 3x as tall but that is not the main difference
The bogie we see has 4 wheels and there are 4 of them in the rear so a total of 16 tires. Add to that the two in the front and you have 18 wheels.
The max takeoff weight is 412 tonnes for the freighter version. That means 26 tonnes per wheel.
The wheels are inflated to 205 PSI compared to around 30-40 that a regular car has. Trucks are around 115 to 130 PSI. This is the main difference between car and airplane tires 5-7x the pressure
The ground pressure of a tire will be very close to the pressure it is inflated too. 26 tonnes=57320 pounds 57320/205= 279 square inch contact area. It looks like the thread is 19 inches which means a distance of 279/19=~15 inches is in contact with the ground. If the pressure was the same as a car tire you need around 86-inch long contact area and it would require enormous tires.
So the answer is they are larger they just look small because airplanes are huge in volume. They have a lot of tires with high pressed and the resulting ground contact area get quite small. It is around 19 inches x 15 inches per tire for a Boeing 747
1. They are only small relative to the size of the plane, a plane is lighter than it looks.
2. They are not normal wheels, they are specially engineered for planes.
3. They aren’t powered, the plane engines provide the movement for the plane, even on the ground.
4. Most of the breaking of the plane is done by special flaps in the wings called landing flaps, some planes also have engines that can reverse their thrust to help with braking.
Best ELI5 I can think of is they are small compared to the size of the plane, just like a fully loaded shopping cart has tiny wheels too. They do the exact same job, just roll, not much else.
Also, the amount of engineering and processing that goes into airplane suspension and wheels compared to cars would make your head spin.
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.
Airplane wheels are huge and they have a lot of them. The look small compared to the size of the airplane. Airplane are compared to the volume lighter then cars or trucks.
Here is a human sitting on the wheels of a Boeing 747 [https://qph.cf2.quoracdn.net/main-qimg-9f2d76bc87612ad7b70333439ddac6e0-lq](https://qph.cf2.quoracdn.net/main-qimg-9f2d76bc87612ad7b70333439ddac6e0-lq) The tire is 49 inch in outer diameter and have 19 inch thread area.
A typical car has 15-19 inch diameter and an area around 9 inches wide. So a 747 tire is 2x as wide and 3x as tall but that is not the main difference
The bogie we see has 4 wheels and there are 4 of them in the rear so a total of 16 tires. Add to that the two in the front and you have 18 wheels.
The max takeoff weight is 412 tonnes for the freighter version. That means 26 tonnes per wheel.
The wheels are inflated to 205 PSI compared to around 30-40 that a regular car has. Trucks are around 115 to 130 PSI. This is the main difference between car and airplane tires 5-7x the pressure
The ground pressure of a tire will be very close to the pressure it is inflated too. 26 tonnes=57320 pounds 57320/205= 279 square inch contact area. It looks like the thread is 19 inches which means a distance of 279/19=~15 inches is in contact with the ground. If the pressure was the same as a car tire you need around 86-inch long contact area and it would require enormous tires.
So the answer is they are larger they just look small because airplanes are huge in volume. They have a lot of tires with high pressed and the resulting ground contact area get quite small. It is around 19 inches x 15 inches per tire for a Boeing 747
1. They are only small relative to the size of the plane, a plane is lighter than it looks.
2. They are not normal wheels, they are specially engineered for planes.
3. They aren’t powered, the plane engines provide the movement for the plane, even on the ground.
4. Most of the breaking of the plane is done by special flaps in the wings called landing flaps, some planes also have engines that can reverse their thrust to help with braking.
1. They are only small relative to the size of the plane, a plane is lighter than it looks.
2. They are not normal wheels, they are specially engineered for planes.
3. They aren’t powered, the plane engines provide the movement for the plane, even on the ground.
4. Most of the breaking of the plane is done by special flaps in the wings called landing flaps, some planes also have engines that can reverse their thrust to help with braking.
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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