Originally posted by Holden McGroin
a 747 airliner, weighs around 400,000 pounds at landing lands at about 130 mph
When touching down, the mains spin up to 130 mph tangential speed within a fraction of a second.
During the chirp of the tires spinning up, the momentum of the aircraft is changed almost imperceptivity. Wheel brakes and thrust reversers are employed to slow the aircraft, which under only air and wheel drag would probably roll for several miles before coming to rest.
This ridiculous problem only makes sense if you suspend disbelief in a conveyor capable of ridiculous speeds. Speed of the conveyor would have to be hypersonic before wheel drag could overcome engine thrust.
Hypersonic speed would destroy not only the gear but the conveyor itself.
Hence under any real world conditions, this problem is stupid.
I agree that it would be impossible to build, or if it were built as best we could it would probably explode after a second or two.
I have landed in light bush planes with big tires, however, the force is more than perceptible.
The point of this question isn’t to debate how such a conveyor could be built, what materials the belt could be made of, how wide or long it must be, what the power source might be. It also does not matter how the conveyor matches the plan’s speed “exactly”.
In the plane speed question, the one where the conveyor only has to match the speed of the plane, the one where the plane takes off, we naturally accept that the conveyor somehow works: power, size, controls and all. It doesn’t matter how impractical it would be to build such a contraption, or that it would be nearly impossible to make one that could handle a 747. It doesn’t matter that some aircraft might experience tire failure when the effective wheel speed is doubled.
The point is that the question brings to light how many people misunderstand the forces at work; that the thrust of the prop is counteracted by the acceleration rate of the plane diminishing into the air drag on the wings and airframe. The extra energy loaded into the wheels at these speed is negligible, not even worth mentioning in this question, the plane takes off. For many people, studying this question opens up a new level of understanding not-so-obvious forces.
In the wheel speed question, if you also just accept that the conveyor exists as described, it opens up a new level of understanding not-so-obvious forces.
