I was watching videos of aircraft landings and noticed how disproportionately small the wheels were on just about every aircraft. Wouldn’t it be better to have larger tires (like in cars) to provide better traction for take off/landing?
In: Physics
Remember that the tires on the car are used to make it go and stop, and to keep it on the road while going through corners. That’s a lot of stress in all directions. The basic function of an aircraft tire is to keep the plane’s body from having to touch the ground, and they do some moderate braking (but the heavy braking is done by reversing thrust on the engines).
Same reason the wheels on a shopping cart are small; they’re there solely for the purpose of rolling. The wheels on a car are what moves the car. An airplane uses it’s propeller/turbofan/jet to push it along the ground, so the weels just need to be there so it can roll.
There are exceptions to this, of course. Airplanes designed to land on dirt and in fields have much larger wheels, and take a look at the back wheels on the landing gear of a Naval aircraft designed to land on an aircraft carrier. They’re much more . . . robust. They need to be to handle the impact and/or the rough terrain. Most airplanes, however, are designed to roll across asphalt, concrete, etc.
Cars use their wheels to push them around and stop themselves quickly to avoid crashing. So they are big and attached to gears and an engine.
Airplanes wheels are not powered, the jet engine pushes the plane around and even though the wheels do help brake the plane most of the force comes from airbrakes on the wing and they often have almost 2 miles to stop!
Also there isn’t much space on an airplane so they are made as small as possible so more luggage can fit in the belly.
on takeoff, the wheels only keep you from sliding side to side, the engines push against the air, not the ground. On landing, you do use them for braking, but an aircraft a given size is a lot lighter than a car or truck the same size.
Bigger tires would weigh a lot more, and take up more space. They’d also have a bigger moment of inertia, so you’d lose more rubber every time you land.
Airplane wheels are only needed as something to land on without messing up the bottom of the plane. All the acceleration and deceleration happens from the engines that move the plane through the air. No force is actually being applied through the wheels.
Car wheels need to have a large amount of surface contact, since that’s where the push forward comes from. It also helps keep traction in turns, and in braking.
Aircraft tires are high profile so it can absorb some of the impact loads on landing, and multiple small tires can distribute the load more efficiently and provide greater safety and stability than an equivalent larger tire.
Cars accelerate and brake using their wheels, planes less so, so they don’t need traction as much. Also the bigger reason cars have larger wheels has more to do with that they have to be able to roll on bad roads, while aircraft usually have a very good runway to use. Look up bushplanes, they are made to land on bad terrain and they indeed have bigger wheels.
As for traction, its more about the material, texture/tred, pressure, and temperature of the tire. Large tires have about the same amount of tire touching the ground, unless they are significantly wider. The smaller circumference of the tires allow them to heat up faster as there is less time for the part of the tire touching the ground to cool off before meeting tarmac and causing more friction… hot tires have better traction. Thats why race car drivers swerve side to side when taking to the track it warms up their tires.
A few reasons… They have a very small space to fit when retracted. The small size also reduces drag, which is crucial during take off. The landing gear will sometimes have multiple wheels stacked together for heavier loads like cargo planes, but they are still relatively small. The larger car tires (scale to size, aircraft wheels are actually much larger than car or truck tires) support much more weight when compare to an airplane of any size.
The wheels arent made to provide big acceleration. Their main feature is that the plane doesnt fall over, can roll and break. And with bigger fires you would have more drag. You prob know those high speed bikes with tiny tiresand cross bikes with huge ones. The tires are just huge, so that it can “climb” better. Not for driving efficiency.
Also smaller tires wheigh less. So the plain has to carry less.
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