re: Myth Busters/Can a plane take off on a conveyor belt

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the obvious flaw with the seaplane example is the much much greater friction of the water and the question as to whether the thrust of the plane would be sufficient to overcome this and move forward

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Yeah, if the current is moving opposite the plane at the same speed the engine is thrusting forward, the plane will move forward, but pontoons in water provide much greater linkage than wheels on a treadmill. It probably wouldn't be able to take off, but it might.

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If the conveyor belt matches the wheel spin, the plane is stationary and doesn't take off because there is no lift created over the wings.

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As has been mentioned, this CANNOT HAPPEN. The jets move the plane. If the conveyor attempts to compensate for the wheel rotation, the rotational velocity of the conveyor and the wheels instantly go to infinity.

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There's the whole key that I think was not placed in the wording when this problem was put on the O-T a long time ago. We didn't know if the conveyor belt was matching the wheel spin.

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Exactly.

I understand the point of the question, and completely understand why and how the plane takes off. But when this topic originally came up on the OT over a year or so ago, it was worded differently. The theories were the same, but the wording of the scenario made it physically impossible.

The conveyor belt moves in the opposite direction of the aircraft and matches the speed of the aircraft.

Ok, I had to go back to the first page to read it again to make sure I had the setup right.

Let's for the sake of argument put a T-38 (one of the planes I fly) on a conveyor belt. The takeoff speed for a T-38 is 162 knots (about 186 mph). We start the experiment by turning on the treadmill as we get the engines going. As the treadmill gets faster, we have to up the thrust of the engine to keep the plane from rolling off the back of the treadmill. We do this until the speed of the treadmill is going at 162 knots.

What will happen? Nothing. The plane will be sitting still on the treadmill, with the wheels spinning really fast.

If any tailwind is created by the treadmill just by the movement of the treadmill belt moving some air, it will be very light. Probably no more than about 5 to 10 knots, which really doesn't cause much of a problem.

The only possible way for this to work for a plane is if the treadmill was hooked up to a gigantic fan that puts out the equal wind speed... or if the treadmill was moving down a runway at the same speed, which would bring up the why have a treadmill in the first place?

I guess this goes with the same with a car. You put a car on a treadmill. The wheels are spinning at 100 mph, the speedometer shows 100 mph, but the car isn't going anywhere. Is it still going 100 mph?

Think of it like this, that plane is already flying and it lands on the conveyor belt causing its wheels to go the same speed as when it was flying. It's still flying. It's just doing it on the ground. It can change altitude and come right off that conveyor belt any time it wants to.

Well aircraft measure their speed by ram air passing through the pitot tube.

However, the plane technically isn't traveling at takeoff speed. The plane will not take off without wind flowing over the wings. Case closed.

If they find a way for a plane to sit still (with wheels spinning really fast on the belt) and somehow create the necessary wind, then it will fly.

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The problem says "travelling at takeoff speed." If speed of a plane is measured by "ram air passing through the pitot tube," then it will fly.

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Then the conveyor belt is moving. Which brings me to my next question... why have a conveyor belt at all?

damn. why is this still going on.
let's keep it simple

plane no fly with no wind (air flowing past wing)

no wind if plan no move.


unless you have one of these bad boys

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