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If an airplane is positioned on a conveyor belt as wide as a runway, and this conveyor belt is designed to exactly match the speed of the wheels, but moving in the opposite direction, ...
Can the airplane take off?
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Message Closed
modified 10-Apr-22 20:24pm.
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Not a joke. A question asked by my friend, for which I am not aware of the answer.
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Degree in physics, as if it mattered: No. The lift depends on airflow over the airplane wings. There will be none.
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Certainly true - as long as you don't fire up the engines. But without the engines running, the plane won't lift even on a normal runway.
The engines will push the plane up to speed, creating that airflow. The push is unaffected by those free-running wheels spinning like crazy - the plane accelerates just as much, wheels spinning or not.
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The engines don't directly cause the airflow. The engines push the airplane, whose movement through the air causes the airflow over the wings.
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So there will be an airflow, and the plane will lift into the air.
The airflow is a consequence of the engines pushing the plane into speed, exactly as at a "standard" take off. The only difference is that the free running wheels will be spinning twice as fast when the plane leaves the ground, but the speed of the plane - relative to the surrounding air and the solid ground - will be exactly as for a normal take off. The air flow in the same.
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Not quite accurate. The airflow over the wings is only part of the lift needed to fly. Modern aircraft are too heavy to use the Bernoulli Principle to fly. Instead they use the redirected air flow from the belly of the fuselage. Watch an aircraft in flight - the nose is always higher than the tail and the plane is staying aloft from Newton's 3rd Law of motion. The force keeping the plane in the air is the air being deflected down by the slope of the fuselage.
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Yes it can, the wheels spin freely and have nothing to do with propulsion, even in normal takeoffs. The Mythbusters even did a show about it.
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The answer is not without wind.
An airplane is lifted off the ground, not because of the speed of the plane, per se.
But because of the speed of the air moving above and below the wing.
The shape of the wing leverages the Bernoulli affect. (High Pressure below the wing, lower pressure above),
giving the plane "lift".
In fact, during a strong wind storm. Planes that are stored OUTSIDE, and TIED DOWN. WILL Lift into the air, and pull against the ropes. Being in Florida, I have witnessed this first hand. It's wild. (And it only works if the plane is facing the wind! The other planes get pushed "down/away" as their wings are "reversed", or they get turned.)
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Obviously yes I would say 
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Not if its speed over the ground is zero.
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I’d argue that it’s the airspeed that matters. If hurricane force winds start blowing during the experiment, the airplane might take off. However the original question didn’t mention anything like that and, under normal conditions, airspeed and ground speed are roughly equal.
Mircea
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It is airspeed that matters, but how fast the wheels are spinning is irrelevant, they aren't what propels the airplane forward.
If you think 'goto' is evil, try writing an Assembly program without JMP.
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Of course you are right. I realized (late) that engines push the air back and, hence, the airplane forward irrespective of wheels moving or not (or even not existing at all as in the case of seaplanes).
Seems my brain was taking a day off yesterday  . Luckily it was a weekend day.
Mircea
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I hear you. My brain takes frequent breaks, and not just on weekends.  I just happened to have argued this same scenario a few years ago (and was on the wrong side at first) and recalled the facts.
If you think 'goto' is evil, try writing an Assembly program without JMP.
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Thanks for an interesting link.
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Other thought experiment: a toy car is on a conveyor, you push it forward and the conveyor goes backward "at the same speed" (whatever that means, which is not quite clear). Can you push it forward?
Whatever the answer, an airplane would do the same thing, because its thrust is applied in the reference frame of the air around it. The wheels are not driven, they spin freely except when the brake is applied.
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Quote: The wheels are not driven, they spin freely except when the brake is applied.
... and that is an important point 
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harold aptroot wrote: a toy car is on a conveyor, you push it forward and the conveyor goes backward "at the same speed" (whatever that means, which is not quite clear). Can you push it forward?
Yes, but you might want to rethink about the problem. Derek Muller was able to show that multiple physics professors at prestigious universities didn't even understand the basic underlying principles.
A Physics Prof Bet Me $10,000 I'm Wrong
It's not exactly the same problem, in the video the propeller will generate a greater force and the vehicle will move forward. Increasing the speed of the conveyor belt will result in an even greater vehicle speed.
The wheels are irrelevant. So are university degrees. 
Best Wishes,
-David Delaune
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Funny you would mention that. As a teen, I did an (I think) related experiment, which is easier to think about.
The setup is like this. Part A: a small lego (technic) car has a gear (which will act as pinion gear) on one of its axles, and you hold a long rack so that it meshes with the gear on the top. Clearly you can push the little car by pushing the rack, it will go at half the speed that you push it.
Part B: if you make a little sliding mount for the rack under the gear, can you still push the car? It turns out that you can, and it makes the car go very fast. That is a sort of similar situation as with that propeller car, except instead of wind there is a rack, and instead of a propeller there is a pinion gear that meshes with the rack.
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Hmmm,
I don't know much about this one.
I was curious as to what you're talking about. I looked it over and the article is referenced from another source:
Sullivan W. (1996). The Secret of the Incas: Myth, Astronomy, and the War Against Time. Three Rivers Press, New York.
Using my ever-improving Wikipedia editor skills, I checked that book beginning on page 41. The reference is based on references from yet another source and I quote 'from a discussion with Gary Urton'. Looks like Gary Urton is guy to contact on this. He probably has alot of free time[^].
Btw that guy has great credibility, you should check to see if there is something you missed.
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