Airplane on a Conveyor Belt
January 30th, 2008So here’s the question of the day:
“A plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?”
Personally, my first thought was that the plane would not take off because it wouldn’t have enough lift without moving up to speed relative to the ground. But after thinking about what it is that actually causes a plane to lift off, the wind going around the wings, I wasn’t so sure.
The wheels in planes aren’t generally what cause the plane to move forward, it’s the suction of wind through the propeller or engines. Presumably the plane would pull the same amount of wind whether or not it was riding the conveyor belt, therefore, I think it would take off.
While you’re taking a moment to think about this problem, let me tell you that tonight the Mythbuster’s are putting this question to rest once and for all. Will a plane on a conveyor belt take-off? (We’ll see tonight, but I think yes).
January 31st, 2008 at 6:18 am
If the conveyor belt is going the same speed as the plane but in the opposite direction, then the plane would not be moving and no wind would pass over its wings. The wind over the wings comes from the plane travelling forward, not from the turbines and propellers.
January 31st, 2008 at 6:45 am
Think about it. The plane would take off in a perfectly normal manner. The wheels would be turning twice as fast and that’s the only difference.
January 31st, 2008 at 11:47 am
Will the plane take off? (Torrent)
February 1st, 2008 at 3:14 pm
Of course the plane would not take off. in order for the plane to take off the plane need to reach a speed known as V2 (this changed for each plane) but the plane is completely stationary, so their is no air passing over the wings due to movememnt. As this is what causes lift, the plane cannot take off, but good question.
February 1st, 2008 at 4:09 pm
Air movement across the wings (Bernoulli’s principle - http://library.thinkquest.org/27948/bernoulli.html) creates lift. The conveyer belt would not affect the movement of air above it. Therefore, since the plane would not be moving relative to the air around it, no lift would be created….and no take off.
-a humble science teacher in Alberta
February 1st, 2008 at 4:29 pm
I love the comments, especially since I’ve seen the episode and understand exactly why the plane can and does take off.
It boils down to the way that airplanes generate their forward momentum—not in the wheels like a car, but from the propeller or engine.
Imagine, Wiley Coyote, wearing roller skates, wings on his arms and a rocket strapped to his back. If he were to try and take-off on a reverse conveyor belt, he’d still be just a likely to lift-off, only the wheels on his skates would be going twice as fast as a normal, non-conveyor belt take-off.
No matter how fast the conveyor belt turns, it produces virtually no resistance to the plane.
February 7th, 2008 at 11:08 am
See Jason Kottke’s liveblogging of the episode.
February 8th, 2008 at 3:29 pm
The comment from “Peter the science teacher” is really showing how deceiving the question is, even for “educated” people. We are so used to vehicles with propulsion coming from the wheels (cars, bicycles, motorcycles etc) that we can hardly think when faced with a different case. The propulsion of an airplane does not originate from the wheels but from the air pressure and air speed produced by either a propeller or a turbine as in a jet engine. Remember that the airspeed produced by the engines that is blown backwards will push the aircraft in the opposite direction, i.e. forward since the surrounding air is standing still. No conveyor belt can stop this. A conveyor belt can only make the wheels spin faster during lift off.
If, on the other hand, there would be a big fan in front of the aircraft blowing air (like in a wind tunnel) at the same speed as the aircraft then the aircraft would not go forward. But it would still lift from the ground since the air passing over the wings at a high speed would produce a force lifting the aircraft from the ground.
Knowledge about Bernoulli is not enough, you have to think too.
Utbildning
http://www.stics.se
February 8th, 2008 at 4:46 pm
I agree.
It’s more of a trick question than a physics question.
February 22nd, 2008 at 7:53 pm
Can anyone provide a detailed description on why (still don’t think it will take off) why…I repeat why the plane will take off?
Pictures, video, etc.. would be greatly appreciated. I would share this questions and answer with my class.
Thanks.
February 24th, 2008 at 7:42 am
“The propulsion of an airplane does not originate from the wheels but from the air pressure and air speed produced by either a propeller or a turbine as in a jet engine.”
But the lift does not. Yes, think.
February 24th, 2008 at 10:15 am
From the “Science Content” section of the Mythbusters show.
Adam and Jamie are standing beside a small treadmill with a model car matching speed with the belt and therefore sitting stationary.
[Emphasis mine]