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MythBusters tackles "plane on a conveyor belt problem"

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Popcorned1    0

No, it will not take off.

Anyway, if the speed was matched all the time it would be impossible for it to take off because there is no air passing by it. Unless you got one of those VTOL aircraft and it just takes off vertically. :p

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The_Decryptor    1,105

I havent read the whole thread, but I have read thru some of the longer replys. What most people who are answering YES are leaving out is the fact that the plane will leave the treadmill...

The people who are saying yes, and saying "yes it will take off", people who are saying no are saying "no it won't take off"

And nice sig btw. :yes:

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jackwanders    0
No, it will not take off.

Anyway, if the speed was matched all the time it would be impossible for it to take off because there is no air passing by it. Unless you got one of those VTOL aircraft and it just takes off vertically. :p

read the thread, then come back here and try again.

sheesh.

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Mx    0

It will take off. As it increases in speed, of course matched by the tredmill, it will stay in the same place, but it then eventually will be at a speed, that the air under the wings will enable it to lift as if on a runway.

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curme    30
MythBusters tackles "plane on a conveyor belt problem"

Posted by Mark Frauenfelder, January 28, 2008 11:13 AM | permalink

200801281104

Last night I spoke to Adam Savage, co-host of MythBusters. He's in Alaska, where current temperatures range between 0 to 30 degrees below zero. He just finished a test on "cabin fever" (he wouldn't say how long he lasted before murdering his cabin mates and running out into the frozen wilderness wearning nothing but longjohns and a sleeping cap) and is now working on another episode up in the 49th state.

But the real reason I talked to him was to find out about the next episode of MythBusters (airing this Wednesday). It tackles the famous "plane on a conveyor belt problem," that has pitted brother against brother and friend against friend for years.

To get to the bottom of the thought-problem, Adam and Jamie used a real plane, in this case a 400-lb ultralight, and a large conveyor belt. Did the plane take off? You'll have to wait until Wednesday to find out, but Adam said even the pilot guessed wrong.

via Boing Boing

At last! I'm sure at least some of you remember the pages and pages of debate, not just at neowin, but all over teh net.

I don't get "Mythbusters", so someone please keep me updated! But if even the pilot guessed wrong, I'm going to say it didn't take off (even though I thought it would).

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neufuse    2,824

You need a certain speed to create the lift to cause a lift off... a standard speed convayer would never create enough... and you will see that in this show

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zivan56    16

I wonder when they will tackle the illusive 1+1=2 problem and if it's true :rolleyes:

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HawkMan    5,181
You need a certain speed to create the lift to cause a lift off... a standard speed convayer would never create enough... and you will see that in this show

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

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curme    30

Just for a quick re-cap:

Airplane-Treadmill problem

Posted by Mark Frauenfelder, December 11, 2006 9:31 PM | permalink

(Update: Cecil Adams of The Straight Dope provides a clear explanation of why the plane will indeed take off.)

David Pogue at the NYT has presented this classic airplane on a giant treadmill problem, and people are arguing about whether or not the plane would take off or not. Here's the problem:

“Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off? “I say no, because the plane will not move relative the the ground and air, and thus, very little air will flow over the wings. However, other people are convinced that since the wheels of a plane are free spinning, and not powered by the engines, and the engines provide thrust against the air, that somehow that makes a difference and air will flow over the wing.”

I say yes. Let's assume the friction in the wheel bearings is negligible. Putting a plane on a treadmill is like putting it on an icy lake. When you fire up the jets, the plane is going to shoot down the lake and take off just like it would on a runway. Link

I've added the comments to this link in the extended entry.

via Boing Boing

Everything clear now? Maybe not. But believe this: The plane takes off.

--CECIL ADAMS

The Straight Dope

I guess we'll see. :whistle:

EDIT: I edited this while Brodel submitted his post.

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Brodel    14

for those that don't know the question..

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

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kylejn    0

I'd say that it'll take off. Can't wait until Wednesday!

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vincent    153

Oh **** ****, it's BAAAAAACK!!!! :o

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serious    1

I can't imagine how he could take off. Lift requires airflow, and this isn't apparent when standing still eventhough the wheels are spinning (by whichever force).

Perhaps I don't understand the question correctly though... the plane stands still, fires off the engines and a conveyor belt moves in the opposite direction, right? The only lift you would get is the ones from the engines themselves, and i bet that's not even close to what's necessary.

But... if the pilot guessed wrong I sure do to.

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zivan56    16

The plane may "take off" if it was tilted upwards with very powerful engines at full power. However, it is a stall takeoff and cannot be controlled without some auxiliary vertical stabilization engines on the wings.

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curme    30

Of course, whatever Mythbusters discovers, will be torn apart mercilessly. They didn't do this or that, they should of done this, etc. But I guess that is true in whatever they do.

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Shof    0

argh....i cant wait for the show

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Rohdekill    730

common sense would answer "no". Lift is required. Lift requires an on coming wind (generated by thrust and nature).

Think of it this way:

Inside a building, you walk on a moving sidewalk in the opposite direction so that you maintain your exact position with the stationary objects around you. If you had a kite, would the kite fly?

Of course not. Even though you are generating thrust, it is negated out due to the thrust in the opposite direction (the sidewalk). You would need to surpass the opposing thrust to achieve airflow, which creates lift.

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serious    1

Well, it turns out most of us were wrong

I searched a bit on the net and the common conclusion among wise men (well...) is that the plane will take of. Someone wrote (after reading some discussions) "Turns out that it doesn't matter what the airplane's wheels are doing, because they spin freely: what matters is the airspeed of the plane. If the plane's moving fast enough with respect to the air, it'll take off."

I find it hard to believe since the only airflow that's created is by the actual thrust of the engines, I just can't imagine how that would be enough to lift the plane

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timmmay    20

So if the conveyor belt is moving at the same speed at all times in the opposite direction of the wheels....then I don't think the plane will take off at all as it shouldn't be moving!

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HawkMan    5,181

The key thing to this thought experiment is wether the converyor could actually hold the plane back no matter how fast itmoves in the other direction.

afterall theplane doesn't move forward by rotation the wheels, the wheel rotation on a plane movement is an effect of the planebeign pushed forware by the throttle.

so that just leaves the weight/mass of the plane pushign down on the conveyor and the conveyor dragging the plane backwards.

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Raa    1,411

Of course it'll take off... didn't anyone read about bernoulli's principle

The engines are creating air movement, the faster that it's doing that, the more air that moves over the wings.

It will lift.... strangely enough.

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HawkMan    5,181
Of course it'll take off... didn't anyone read about bernoulli's principle

The engines are creating air movement, the faster that it's doing that, the more air that moves over the wings.

It will lift.... strangely enough.

The engines don't make the air move over the wings.

the engines move the plane forware wich make air move over the wings. Witht he exception of propeller planes where the prop will make air move over a small part of the wings, but not enough to lift the plane without the plane moving forward.

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solo.man    0

There's two issues involved, and yes, the plane will both move forward and take off, assuming:

A. the friction between the wheels and the conveyor belt is within realistic bounds.

B. the air is not moving along the same vector as the Airplane.

If those two are true, then the conveyor belt is irrelevant since it hasn't got the "grip" to hold the plane to it's surface, therefore the plane will take off as usual.

If however, which wouldn't be possible in reality, the conveyor belt generated enough friction to keep the airplane on itself, then, yes, the plane would still take off, as long as the conveyor belt was moving fast enough in the right direction, otherwise, no.

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curme    30

The important part to remember is:

Did the plane take off? You'll have to wait until Wednesday to find out, but Adam said even the pilot guessed wrong.

If the pilot guessed wrong, it must be the opposite of what everyone assumes.

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teriba    2

It depends on how it is performed. There are two separate ways to look at it and from the wording of the problem you can't really tell what they mean. Without this being clarified you can't answer it.

Fact - You need positive ground speed to take off in a standard jet. Wheel speed is useless, except for tire ratings (your tires will blow when they are spinning too fast).

Case #1 - Assuming friction in the wheels

If there is friction in the wheels then the conveyor belt will be able to impart a force on the plane. The conveyor belt can run at a speed sufficient to keep the plane motionless and it cannot take off because there is no groundspeed. But, the conveyor belt must be running far faster than just the planes speed in the opposite direction to hold it back. So based on the wording it might still take off.

Case #2 - No friction

If there is no friction the conveyor belt will not impart any force on the plane, no matter how fast it is spinning. The only thing that will happen is the tires will spin faster. The plane will accelerate and take off as if it is on a normal surface.

Personally I think they mean case #2 when they describe the problem in which case the plane will take off fine.

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