Plane on a Treadmill

[Yume]

A plane equipped with fixed horizontal engines and wheel landing gear is placed on a huge treadmill runway. The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction. Will the plane take off and fly or not?

If you've got half an hour to kill (hello people at work), check out this link, watch the video and read the ensuing thread. It's hilarious. Maybe only to science nerds.

http://www.meignorant.com/plane_Moz

[Snow]

Will the plane take off and fly or not?

Im curious how much the laminar flow over the treadmill would affect this

[Equivocal]

Perhaps I fail at understanding the physics of the system, but it seems to me that regardless of what's happening with the speed/treadmill of the problem, a plane by definition only functions by the speed of the plane displacing surrounding air underneath the wings causing lift when combined with a bit of a tilt to allow that force exchange to occur.

If the plane does not move on the X axis (because moving on an equilibrium of a treadmill makes for a lack of delta X), I would think that no (significant amount of) air would be displaced, and no lift would take place.

Unless the treadmill suddenly stopped.

Hmm.

[Yume]

The spinning of the treadmill in turn moves the wheels of the plane which rest on a nice free spinning frictionless bearing which does not translate into any force to counteract the force of the jet engines meaning that the plane moves relative to the air at its own speed without being affected by anything on the ground.

So we've established there's inequal forces at work (plane generates thrust and the movement of the treadmill doesn't to jack to stop it) so the plane moves relative to the air, air moves over the wing, and plane takes off.

Im curious how much the laminar flow over the treadmill would affect this

I swear i'm going to modify the phpbb source so that big words you use automatically link to their wikipedia entry.

http://en.wikipedia.org/wiki/Laminar_flow

Of course in this case it's all Greek to me how you are applying this concept in this manner so I'm going to say it's negligible relative to the actual motion at hand.

[Equivocal]

The spinning of the treadmill in turn moves the wheels of the plane which rest on a nice free spinning frictionless bearing which does not translate into any force to counteract the force of the jet engines meaning that the plane moves relative to the air at its own speed without being affected by anything on the ground.

So we've established there's inequal forces at work (plane generates thrust and the movement of the treadmill doesn't to jack to stop it) so the plane moves relative to the air, air moves over the wing, and plane takes off.

Ah, I was under the impression the movement was solely from the wheels, not the jet engines.

So, the plane would take off from the air displacement, but then would cruise significantly away from the treadmill. <_<

[Snow]

Perhaps I fail at understanding the physics of the system, but it seems to me that regardless of what's happening with the speed/treadmill of the problem, a plane by definition only functions by the speed of the plane displacing surrounding air underneath the wings causing lift when combined with a bit of a tilt to allow that force exchange to occur.

Well the high-school physics description that I was given way back when was that the wing shape indirectly causes lift: air has a longer path over the top than the bottom of the wing and travels faster over the top as the plane slices through it resulting in more dynamic pressure above than below, which causes more static pressure below than above. The difference in pressure (more static pressure below than above) causes lift.

The spinning of the treadmill in turn moves the wheels of the plane which rest on a nice free spinning frictionless bearing which does not translate into any force to counteract the force of the jet engines meaning that the plane moves relative to the air at its own speed without being affected by anything on the ground.

So we've established there's inequal forces at work (plane generates thrust and the movement of the treadmill doesn't to jack to stop it) so the plane moves relative to the air, air moves over the wing, and plane takes off.

Im curious how much the laminar flow over the treadmill would affect this

I swear i'm going to modify the phpbb source so that big words you use automatically link to their wikipedia entry.

http://en.wikipedia.org/wiki/Laminar_flow

Of course in this case it's all Greek to me how you are applying this concept in this manner so I'm going to say it's negligible relative to the actual motion at hand.

What I am saying is that you are forgetting a force here: the treadmill "pushs" the layer of air just above it, causing it to move. ie I would expect to get laminar flow of air above the treadmill. A more interesting question would be, what happens if the plane had no engine and the treadmill was really really big?

[Androk]

If the wheels on the Plane are frictionless, the force exerted on the wheels from the treadmill will be exactly the same as the force of the wheels resisting movement from the treadmill. So, any other force exerted on the plane will move it.

Think of it this way. If you're holding a toy car(with super cool frictionless wheel bearings) on a belt sander all forces are equal. Now use your hand to push it off. The force you use to move it with your hand is the exact same thing as thrust from a jet engine.

So yeah, with those being the only relevant forces acting on it the plane will take off.

[shiv_]

The spinning of the treadmill in turn moves the wheels of the plane which rest on a nice free spinning frictionless bearing which does not translate into any force to counteract the force of the jet engines meaning that the plane moves relative to the air at its own speed without being affected by anything on the ground.

So we've established there's inequal forces at work (plane generates thrust and the movement of the treadmill doesn't to jack to stop it) so the plane moves relative to the air, air moves over the wing, and plane takes off.

Im curious how much the laminar flow over the treadmill would affect this

I swear i'm going to modify the phpbb source so that big words you use automatically link to their wikipedia entry.

http://en.wikipedia.org/wiki/Laminar_flow

Of course in this case it's all Greek to me how you are applying this concept in this manner so I'm going to say it's negligible relative to the actual motion at hand.

He was just trying to sound like he is actually getting an education at MIT instead of playing wow for a living. D: ?

[manx]

a. the tires will burn off and it will shoot off the back of the treadmill

b. the tires can handle unthinkable amounts of wear and tare and it will roll off the front of the treadmill.

since the wheela are working against the treadmill and the engines are working against nothing but air, wouldnt the wheels reach like a rotation lvl of infinity and then wouldn't the plane shoot off the front of the treadmill?

*edit- just thought about it a bit more, it would look just like a plane taking off on a solid surface speed wise.... the only way to keep the plane stable would involve the use of a wind tunnel to counteract the engines or whatever, which isnt part of the question... so my final answer is no, the this equation cannot exist in a perfect world! I think snovv pointed out that this equation would be much more interesting if the plane was propelled by its wheels.

[shiv_]

After actually reading the post I am not interested, but I am still going to leave my previous post up for good measure.

Doesn't a plane need to have acceleration in order to get lift? D:

If it can't accelerate how does it take off?

Maybe I should just watch the video

[Snow]

After actually reading the post I am not interested, but I am still going to leave my previous post up for good measure.

Doesn't a plane need to have acceleration in order to get lift? D:

If it can't accelerate how does it take off?

Maybe I should just watch the video

Dont plane models experience lift (which is measured) in wind tunnels when they are stationary? (I actually dont know much about fluid dynamics or aeroengineering so I admit I could be wrong).

ps the server needs to come up so we can stop talking about this

[manx]

the server is down? I was wondering why there was all this love on the forums!

[Lemmiwinks]

Thought experiments that sporadically ignore reality are fucking stupid.

It's like arguing theology with someone that thinks that God can make 2+2 not equal 4.

[futureal]

Dont plane models experience lift (which is measured) in wind tunnels when they are stationary? (I actually dont know much about fluid dynamics or aeroengineering so I admit I could be wrong).

Any type of model, plane or otherwise, experiences lift/drag/something in a windtunnel because of the air flowing around its surfaces. In the case of a plane in a wind tunnel, there is no thrust involved -- it is simply the flow of the air around the plane's surfaces. The air pressure above and below the wings of a plane becomes unequal due to this flow, and lift (or negative lift, depending on the orientation of the wings, aerilons, etc) is created.

Whether or not the plane is actually moving is irrelevant. What is relevant is whether there is a difference in air pressure above/below a surface, which creates lift or negative lift. This would mean that either the air has to be moving relative to the plane, the plane has to be moving relative to the air, or both. However, in this example, the air is not moving and the plane is not moving.

As long as the treadmill continues to cancel out the movement that would be generated from the plane's thrust, it will not "take off" or do much of anything. End of topic.

[Androk]

The question I got from the video wasn't wether it would leave the ground, it was wether the plane would move forward off the treadmill. I don't think the treadmill causing some kind of airflow over the wings was ever part of the equation.