Brain-teaser: Will this plane fly?
 

I found this on another car site and it was fun to see people trying to figure it out. If you think you know the answer try to back it up with an explanation. Btw, there is only one answer and the type of plane doesn't make a difference. But to help simplify the discussion let's assume a plane with fixed thrust vectoring. So we aren't talking about anything that can take off vertically.

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The question is: Will the plane take off or not?

The plane is not being driven by the friction of the wheels on the belt. It is being pushed(assuming jet) by the engines against the air. The belt would not affect the speed of the aircraft other than the wheels would be spinning twice as fast. The plane will take off.

yes it will becuase once the plain reaches its spped to take off it, it will lift up with the conveyer not having an effect

What he said. But I think he means the plane will NOT take off. Only way it would take off if it was a Harrier. Then it could take of vertically. :cool:

the plane uses the moving air under its wings to lift it, not the wheels. no matter what the speed of the belt, the plane will lift because the energy lost to friction in the planes wheels(spinning backwards because of the belt) is not great enough to overcome the planes engines.

the plane will take off.

The plane isn't moving.

The plane will not take off. As ho1ywars stated, the plane uses air under its wings to lift. If the plane is on a conveyer belt, it would be standing still(think running on a treadmill). The plane will get no lift by standing still.

Wait I just got what you guys are saying. But I still don't think it would take off. I think it would still run off the conver belt.

Edit: confused at this point. But I don't think it would take off.

The engines on the plane don't cause lift. The air moving across the wings does though. Plane not moving = no air across wings.

It's all relative to air speed not ground speed. Ponder this...A plane flying 450 mph flys into a 450mph headwind, the plane is essentially standing still over ground but it is still flying due to the air speed over the fuselage of the aircraft.

the plain is moving. and any plane now adays would beable to do it, as long as the conveyer belt is jumped up to a bigillion mph right away. wheels have bearings in them, causing very little friction. the plane motors can easly over come the conveyer belt when they are up in rpms, is just a matter of can they get there before the conveyer belt ends and then topple off.. right?

if the planes engines are up to speed, its going to fly, probably any plane built now adays can i think.

Right, it's already been said, but no, it will not take off. Think of trying to climb up a down escalator. If you're going up at the same speed that the escalator is going down, you stay in exactly the same spot (though the muscles in your legs will disagree). Gotta love relativity...you're moving at take-off speed in relation to a point on the belt, but it's movement in relation to the earth (for lift) that matters.

I agree with him. THats what I meant to say I just didnt know how to explain it.

that doesnt make sence. if the plain is traveling sixty miles per hour, the belt matches that. the plain wheels will be doing 120, but the plane itself is only doing 60, enough for take off. planes use air rasistance(is that the right word?) to propell them, not the wheels.

Although, I'm going to disagree with myself only under the following exception. Think of riding on a train that's going at X mph east, and you throw a baseball towards the back of the train X mph (west). Like I said before, in relation to a 3rd party observer, the ball is standing still. However, if the train is a closed environment, it'll seem as if the ball is traveling west at X mph. SOOOO, if there was some intermediary between the belt and the plane that allowed it to pick up "air" speed, it would be able to take off (like a giant corridor). However, I think the question assumes otherwise.

Reread it...the belt is moving in the OPPOSITE direction. Think vectors, +60 and -60 don't equal 120, they equal 0.

no you reread it, if the belt alone is going sixty, and the plane alone is going sixty, the distance the wheels travel is both, 120. take a freaking matchbox car. put it on paper. put it at the end. mark one of the wheels. now push the match box car from one end of the paper to the other, count the wheel turns. now do it again, this time, move the paper in the oposite direction, yoru gonig two need to pieces of paper, in order for the car to move the same distance.

im a ****ing moron, i dont know how to explain ****.

120 is assuming there is no friction too, but ofcourse there is, so drop a few mph off of that.

What you're saying is that the belt is moving the wheels as well as the engines. This would be the same idea as what you said...pull the piece of paper from underneath the matchbox car in the opposite direction. That would be the case if the plane was suspended and the wheels were able to respond to the moving belt. BUT, from the perspective of the wheels (here comes that relativity again), the belt IS the ground...it's not moving freely under the wheels. Think of driving down the road, but the road is actually moving as one piece the opposite way. You're moving X mph relative to the road, the road is moving X mph the other way in relation to the earth, and your motion in relation to the earth is zero.

there is no air going under the wings so it wont take off.