Plane Treadmill

[Karby]

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

Source: http://answers.google.com/answers/threadview?id=428718



Discuss.

[Tache]

No

[Anthaya]

No

Nice dicussion. :) but yeah I agree. After looking at all the posts on that thread half of the people I don't think understand how simple this question really is. But, if I'm right, the plane actually takes off from the wind acting on the wings it gets from speeding up during take-off and thus no matter how fast it's going on the treadmill it will ultimately be stationary and thus there won't be any real wind pressure on the wings except from the wind blowing. But I don't really know much on this I'm a math teacher so this is not something i know too much about.

[Tache]

This whole thing is bullshit.

The real question to answer is whether or not the plane moves relative to the ground or not. If it does, it takes off. If it stands still, it does not. It has nothing to do with thrust vs. wheels etc, a plane takes off because of lift created by air over and under its wings, thus the plane has to move to take off.. so, does it move kids?

[Anthaya]

This whole thing is bullshit.

The real question to answer is whether or not the plane moves relative to the ground or not. If it does, it takes off. If it stands still, it does not. It has nothing to do with thrust vs. wheels etc, a plane takes off because of lift created by air over and under its wings, thus the plane has to move to take off.. so, does it move kids?

I don't move relative to the ground when I'm on a treadmill so i guess it's the same for the plane. Which is the reason I said no.

[Leftquark]

I work at an Aerospace company and decided to ask some of the guys at work. I'm sure Arkinia could ask people at his work since he and the rest of them know a ton about planes as well, but here's what I got as answers:

I’m going with take off now.

This convinced me. I’m also assuming the thrust of the aircraft is much larger than the frictional forces between the wheels and the conveyor.



But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.

And another one:

The treadmill can be doing what ever it wants...the propeller is moving the entire craft forward...the tires will just be going twice as fast. It WILL take off. Since the propeller (turbine engin, whatever) is moving the entire craft forward, there will be wind generated which in turn creates lift over and under the wings which will allow the plane to take off. The fact that it's on a conveyor belt only moves the wheels at a different speed, which will not effect the forward motion caused by the propeller pushing the plane forward.

[Wintermute]

"A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?"

This problem statement is misleading and incomplete.

In order to have a definitive answer you need to have qualifiers which define the paramaters of the problem. Such as:

Does the plane have its engines on at a thrust level required for takeoff?

Are the frictional forces between the aircrait and its wheels negligable?

Is the treadmill longer than the required takeoff roll of the aircraft?

Is the aircraft in questoin any variation of one of the following: V-22, Yak-38, Mirage IIIV, F-35, or AV-8?

Otherwise, certiain sets of assumptions will support either yes or no answers.

[Mirkendargen]

The question is is air traveling across the wings? Given this situation, it might or might not, depending on the thrust this plane can put out compared to the rolling and kinetic friction on the tires and wheels.

What would probably happen is after a few minutes you will burn your tires off, snap the gear, and die in a plane fire.

But, since the wording of the question is tricky, you get another option. It says the "speed of the plane" and which implies that the plane has to be moving, or the treadmill is just chilling and doing nothing. So for a simplified equation to prove it true/false, if (thrust) - (rolling friction) - (kinetic friction on axle) > (air drag at takeoff velocity), then the plane takes off. The kinetic friction of the wheel on the axle is the only point and the maximum value of force that can be transfered to the plane from the treadmill.....unless those axels REALLY suck and the kinetic friction on them is greater than the static friction between the tires and the treadmill, in which case the tires would begin sliding, and the kinetic friction between the tire and the treadmill would be the maximum amount of force imparted on the plane.

Someone actually involved in aerospace would have to provide actual values on these things, but once that's done it's just plug and chug to see if it's possible.

[Anthaya]

An emo kid is standing on the edge of a bridge that can move (like a giant conveyor belt) and wants to jump off. This conveyor has a control system that tracks the kid's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will he be able to kill himself?

Discuss.

[Mirkendargen]

He'd get his ultra baggy pants caught in the treadmill and shred his face on the mat part of it.

[Selva]

Since the treadmill moves at the exact same speed as the plane I'm going to say it accelerates instantaneously.

So no matter how fast the engine can push it won't be able to create and force relative to the earth, it would only make the treadmill move faster.

So the answer is no.


Left your friends assumed that somehow the engine would move the plane forward, which means they misread the question. The point of the question is that the treadmill would cancel any movement relative to the earth.

Well at least in my interpretation. The answer directly relies on how you want to view the treadmills reaction to the plane.

[Bleedo]

The treadmill spinning in reverse of the planes direction still won't be able to stop the plane from moving forward. It doesn't matter if the treadmill is spinning at 1 rpms or 83976892768927 rpms, the thrust from the planes engines are still going to pull it through the air, causing lift. In fact, you could remove the planes wheels and it would move forward on it's belly as well, granted that'd cause severe damage to other parts of the plane which would prevent takeoff, not to mention the drag it would create... you'd need some pretty big engines to generate a greater amount of thrust.

It'd be like if you had skates on a human treadmill. You could set the treadmill to go like 200 mph and you'd still be able to pull yourself forward via the handlebar, assuming the bearings on your skates didnt fall off and hurt you beforehand.

again, A treadmill/conveyor going in reverse won't stop a plane from moving no matter how fast it goes... the plane moves forward relative to the air around it, not the ground.

[Baaguk]

A plane gets its forward movement from engines pushing air either through or past them, unlike a car (which they obviously want you to think about) which gets its forward movement from pushing ground either through or past them.

So... since a car gets its movement from pushing against the ground, using a treadmill to move that piece of ground versus the car's push would work.

AND since a plane gets its movement from pushing against the wind, if they could somehow move that piece of air that's getting sucked in and spit out at speed THEN the plane would never take off.

[Buba]

I like pie!~

[Selva]

again, A treadmill/conveyor going in reverse won't stop a plane from moving no matter how fast it goes... the plane moves forward relative to the air around it, not the ground.

That is correct. That is how the treadmill and airplane would respond to each other.

However, the topic at hand is whether or not the plane would lift off.

So yes the airplane could generate force relative to the earth. However, if the airplane isn't off the treadmill instantly then the force would disperse to the treadmill.

Using your example of skates on a treadmill. Keep in mind that this is, so to speak, a magic treadmill that adjusts instantaneously to your speed. So if you were to push yourself forward, the energy you just created would be isntantly matched by the treadmill.

But a person could push up against the handrails and lift themselves off the treadmill. Thus using yourself to use your enviroment to remove yourself from the treadmill. The same as the airplane's engine using the air around itself to lift off.

So you are correct in theory.

However, there isn't a vehicle on earth that could generate enough thrust instantly to prople itself off the surface of the earth.

You would probably need to create a hurricane's worth of force in an instant to lift something as dense as an airplane using air.