Will a plane on a treadmill take off?

OK, I have seen this question posted on a couple other message boards I go to, but seeing asd most of the people at those messageboards don’t have a large knowledge of physics, I am posting here in hopes to get the correct answer.

Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Can the plane take off?

I say no, because the plane will not move relative the the ground and air, and thus, very little airflow will occur over the wings (the engines will create a small amlunt, but not enough.) However, other peopel 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.

So what’s the real answer here>

You need to reassure me that the other people were joking or we are going to start taking away voting rights.

Airspeed is the only thing that matters to an airplane. The speed of the wheels has nothing to do with anything. You need air flowing very quickly over the wings and tail to generate lift.

The only time an airplane can take off from a very low groundspeed if it was facing into a very strong headwind. Some small planes have been know to hover relative to the ground if they are flying directly into a very strong wind.

How would that work? Would you have a sensor that monitors the rotational speed of the wheels and runs the conveyer accordingly? Let’s say you pulled the plane forward using a rope attached to a truck not on the treadmill. Wouldn’t this cause feedback between the wheels and the treadmill to cause the treadmill to speed up to infinity? And beyond?

Yeah, that’s what i thought. but some of these peopel almost seemed to know what they were talking about. Well, not so much the “thrust is from the engine and has no effect on the wheels” people, but there was another line of reasoning for why it could take off.

OK, I found someone’s explaination:

So basically they are saying that even though the magic runway matches the speed of the wheels on the opposite direction, that dosen’t matter, because it merely makes it slightly harder for the plane to move, but the plane will still move forward.

The plane would not sit there on a treadmill with just its wheels spinning either. It is the thrust of the engines that moves the plane forward, not the effect of its wheels on the ground. The wheels wouldn’t exert any backwards force on the treadmill, so it wouldn’t start to move. The plane would just move forward off the treadmill (and would eventually take off as normal).

That sounds right to me. The wheels aren’t the things that are accelerating the plane, so the treadmill doesn’t really do anything except spin them faster as the plane takes off.

I need names and voting jurisdiction. This is too unbelievable for words. I can actually relate to those Snopes type things a lot better than this.

That Newton. What a kidder.

The engines, wings, and air don’t know a thing about the conveyor belt. The engines push, the plane moves forward and continues to do so unless acted upon by some other force. The engines push harder, the plane moves faster, and eventually it takes off, while the wheels (and the conveyor belt) are moving at some multiple of the plane’s takeoff speed, how fast depends on how much acceleration the conveyor belt has behind it.

Please go find this person and take away the ballpeen hammer with which they’re hitting themselves in the forehead.

In your OP, basically you’d have a very loud, very big machine standing very still (relatively speaking). Just go back into that other thread, scream BERNOULLI! at them, and leave. Let them figure it out.

But you seem to be thinking that the conveyor build is actually conveying the airplane backwards at the same speed as the engines are moving it forward. But that shouldn’t be the case unless the pilot has the brakes on. Otherwise, it’s fairly easy to move the airplane against the force of the treadmill.

A thought experiment. Suppose you’re on the treadmill at the gym and someone sets the speed to “WHOAH!”. You’re going to go flying backwards. Now, suppose you have rollerblades on. With just one finger wrapped around the handbar, you’d be able to resist the force of the treadmill no matter what the speed was set to (up until the bearings on the rollerblades started smoking.)

Now, imagine someone gave you a Wile E. Coyote-style Acme rocketpack and lit it off. What direction do you think you’d go?

I still want an explanation of the feedback between the wheels and the treadmill. It sound like any foward motion will cause the treadmill to speed up to the point where it bursts into flames. How does the plane take off from a high speed flaming conveyer belt? Unless the speed of the belt generates a headwind sufficient to let the plane take off vertically… yeah, that might work…

All I know is that when I fly, the plane has to touch down every so often in order to regain speed.

I’m with pmwgreen on this.

If it were an automobile on the treadmill, you can program the treadmill to match the speed of the wheels and make the vehicle. It’s possible because the vehicle is trying to move by pushing on the treadmill surface, and you’re moving the treadmill surface so it can’t be pushed.

If you put an airplane on the treadmill, the airplane accelerates by pushing on the air, not the treadmill surface. If the treadmill is programmed to try to keep the plane in one spot, it will move faster and faster to try to stop the plane, but fail to do so. The plane will still move and take off. Unless the treadmill can move so fast that it overheats the wheel bearings of the airplane and causes them to fail.

I agree that the jet would surely take off, but as a thought experiment the belt is confusing.

Suppose for this thought experiment that a laser was monitoring the jet wheels and the throttle on the belt. Every little forward movement of the wheels caused an equal increase in belt speed.

Given that the jet would take off, how would the wheel/belt situation resolve itself?

Well, yeah, the physics of the conveyor belt don’t really work out unless the wheels are the only thing driving the plane. Otherwise you’re going to have to spin the conveyor belt at infinite speeds. (Or, in real world, fast enough so that the wheels would start slipping, because there’s only so fast you can drive them. The plane would take off amidst burning rubber and smoke. * Landing * would be a real problem.)

The question that needs to be asked is what is going to generate the lift?

Wait, scratch that. “With every detected increase in wheel speed…”

Sorry. I’m confused.

The bold is the technicality here, if the 2 match exactly the plane can’t move unless there is skidding. I suspect within a foot of travel the belt would be traveling a good portion of the speed of light however. Practically the tires would blow, the wheel bearings would overheat, seize (both giving a great deal of resistance to the forward motion).

Perhaps the belt can generate a wind high enough for the plane to lift off at zero speed.

No, you’d get a plane taking off from a big loud treadmill.

The plane is driven forward by the jet exhaust - tons of air moving at high speed, not by the action of the wheels. You can work it out from conservation of momentum or by keeping the center of mass of the system (plane + exhaust) constant, but no matter how you look at it the plane will move forward.

Suppose that the plane was being towed forward with a rope (the towing mechanism being located on solid ground, not on the treadmill). It’d certainly move forward no matter how fast you ran the treadmill, right? Same thing.

And IIRC the Bernoulli equation isn’t really what’s keeping a plane aloft, it’s conservation of momentum of the fluid flow over inclined planes (wings/flaps).

Thanks Dag Otto. But just in case that’s not enough:

OK, instead of a treadmill – which as people have pointed out, has some problems with infinite speed – consider that you have a perfectly smooth, flat, and slippery surface. For a car, that has the exact same effect as the treadmill – if you rev the engine the car spins its wheels and doesn’t move, right?

Now, what would happen to a plane on that surface? Just to make it easier, call the surface ‘ice’

Or, as Otto might have said “All I know is that skiplanes, floatplanes and other planes without wheels can never possibly get off the ground.”