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
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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