|MadSci Network: Physics|
That is a great question. It does seem hard to believe that something as massive as an airliner can come slamming to the ground at 150 mph onto those little wheels. Personally I sometimes find it even harder that something as massive as a 747 can fly at all! It astounds me every time I think about it. But we see them fly, and land on those small wheels, so we know it's possible. Even though it seems like it, we also know that it's not some freak of nature. The teams of engineers that design these technological marvels have calculated the forces, stresses, material and design strengths so that it all works. So I guess that is the answer to your question - because the engineers say so. :-) There are a couple of things I might point out that may make it easier to swallow. First, airliner wheels are anything but small. As tall as a person, the wheels only look small because they are next to the really big plane. Second, the wheels carry the plane for only a short distance. The wheels only make turns when the aircraft is going very slowly, this prevents lateral forces from being transmitted through the wheels. When the aircraft is going at its fastest ground speeds, just before take off and after touch down, most of the aircraft's weight is being supported by the wings. Except for taxi, direction control of the aircraft is mostly via the flying surfaces and the wheels are only along to support some of the weight. This is not to say that the wheels do nothing at all. The concrete in the landing zone of the largest airports is 12 feet deep! You are also right that in a cross wind the wheels will bear much of the lateral load caused by the wind. This is part of what sets the limits for maximum cross wind that all planes carry. The giant C-5 Galaxy has addressed this problem by using gear struts that rotate so that the aircraft can land crabbed into to wind. I hope I have answered you question. Thanks for asking. Dave Leonard Navy Flight Surgeon
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