MythBusters tackles "plane on a conveyor belt problem"

By The_Decryptor
in Science News & Discussion

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Grand Master

Menge

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the place where people fail in this problem is that they can't visualize that the wheels of a plane do nothing apart from keeping the plane with minimum resistance to the ground (hint: they're FREE). they don't propel the plane by pushing on the ground - the ENGINE pushing the AIR does.

people also say "the airflow from the engines won't be enough". that's right in the sense that the airflow from the engine alone can't lift the plane. but wrong cause there won't be JUST the airflow from the engines - because the plane WILL move forward regardless of the speed of the conveyor in the opposite direction (remember the wheels are free and the engine pushes on the air), so there will be the engine airflow PLUS the movement of the plane's airflow.

i bet that it'll take off.

Grand Master

DrunkenMaster

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The laws of physics should be universal right? I say yes, plane will take off. I've a previous experiment to verify my hypothesis. So lets say my test case is a human running on a treadmill, call him the unexpecting classmate. Now, if unexpecting classmate can go flying-off a treadmill - and humans are not meant to fly - does this not mean that same principal applied to an airplane, which is meant to fly- would work? I think so.

*This is wrong on so many levels, including experimenting on humans which I do not condone.

Grand Master

gigapixels Veteran

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All I have to say, is... think about a wind tunnel.

This has nothing to do with a wind tunnel. Only the conveyor belt is moving, and a conveyor belt moves no air, and thus no lift.

Grand Master

HawkMan

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All I have to say, is... think about a wind tunnel.

a wind tunnel is a cmpletely irrelevant comparison here. the wind tunnel creates wind motion across the entire plane as if it was moving.

The engines won't, however, the engines will most likely have more than enough power to push the plane forward faster than the conveyor belt can move to keep the plane back by friction.

However, I'm pretty sure the pilot knew all this and guessed that the plane would take off, afterall that is the point behind the whole tought experiment in the first place. so if the pilot guessed wrong... well either he's a stupid pilot who said it wouldn't take off, or somehow the plane didn't take off.

Rising Star

serious

Posted
Posted
the place where people fail in this problem is that they can't visualize that the wheels of a plane do nothing apart from keeping the plane with minimum resistance to the ground (hint: they're FREE). they don't propel the plane by pushing on the ground - the ENGINE pushing the AIR does.

people also say "the airflow from the engines won't be enough". that's right in the sense that the airflow from the engine alone can't lift the plane. but wrong cause there won't be JUST the airflow from the engines - because the plane WILL move forward regardless of the speed of the conveyor in the opposite direction (remember the wheels are free and the engine pushes on the air), so there will be the engine airflow PLUS the movement of the plane's airflow.

i bet that it'll take off.

Hold on a minute, isn't the conveyor moving as fast as it is necessary for the plane to stand still relative the ground?

Grand Master

gigapixels Veteran

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The thought experiment specifies that the conveyor belt can move fast enough to keep the plane in place, so if the plane goes faster than the conveyor belt the physical experiment has been done wrong.

Hold on a minute, isn't the conveyor moving as fast as it is necessary for the plane to stand still relative the ground?

That's what I thought. I think the only reason people get confused about this problem is that they are unclear on this point. If the plane is standing still relative to the ground it will not take off.

Grand Master

jimbo11883

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This has nothing to do with a wind tunnel. Only the conveyor belt is moving, and a conveyor belt moves no air, and thus no lift.

What I meant was, in a wind tunnel, the plane never moves from its position, but will (possibly) fly because of the air moving in the tunnel. If a plane was to fly with the conveyor belt experiment, it would need to be pretty windy outside, because if the plane is not moving anywhere, there won't be any lift.

Grand Master

gigapixels Veteran

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What I meant was, in a wind tunnel, the plane never moves from its position, but will (possibly) fly because of the air moving in the tunnel. If a plane was to fly with the conveyor belt experiment, it would need to be pretty windy outside, because if the plane is not moving anywhere, there won't be any lift.

Still, wind should not be any sort of factor in this experiment. The point is whether or not a moving conveyor belt can cause a plane to take off, which it cannot.

Grand Master

neufuse Veteran

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the plane on conveyor belt myth/thought puzzle isn't about getting the plane to take off, just FYI :)

That's wierd because on the TV commercial they said "Adam and Jamie tackle the myth of if a plane is on a convayer belt, will it take off?" seems to be about taking off to me :p

Grand Master

AJerman

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Yes, if velocity = 0, there is no lift.

However, velocity != 0, so that's irrelevant.

Anyway, at least it seems like most of you on here are smart enough to know it will take off. I was on another message board and most of them can't seem to get it through their heads how jet engines work. Ahh well. :p

Umm...if the myth were true and the plane did have a chance to take off, wouldn't the military have taken advantage of such a thing on aircraft carriers to reduce runway size?

No, because it takes the same amount of runway to take off. It doesn't sit still then take off, it moves forward just like if the ground wasn't moving.

Grand Master

jimbo11883

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Umm...if the myth were true and the plane did have a chance to take off, wouldn't the military have taken advantage of such a thing on aircraft carriers to reduce runway size?

Exactly. These fools that think it will fly, ROFL!

Grand Master

jimbo11883

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Curious why velocity != 0 if it will be stationary...

^^ By the way, the military wouldn't shorten the runways, or else how the hell would the planes land?? haha didn't think of that one did ya?

They can land on the conveyor belt! :woot:

Grand Master

HawkMan

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Umm...if the myth were true and the plane did have a chance to take off, wouldn't the military have taken advantage of such a thing on aircraft carriers to reduce runway size?

They do.

The Catapult is essentially a realy fast conveyor belt, just without the belt since planes have wheels that rotate freely :)

Grand Master

Menge

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it WONT be stationary. the conveyor will be moving back at the same speed as the plane's forward speed. but the trick is that the plane's speed is NOT dependent on the GROUND (otherwise how the HECK do you think it flies after leaving the ground?!). the plane moves by pushing the air back and not the ground back.

so what happens is that the conveyor's speed is totally irrelevant to the plane. it will still move forward, because it doesn't depend on the ground to move forward (only to keep it from "falling to the center of the earth" while it doesn't have enough windspeed to sustain itself).

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