Think your smart?

[Stangster5.0]

This is way off topic for this forum but I had to do it ,sorry admin.I got this off of another forum I belong to and take no credit for the question.I was the only one to get this right and it really is a tricky question.Ill post the link to the forums afterwords if anyones intrested.

A plane is sitting on a conveyor belt that covers the entire runway.The conveyor belt spins in reverse the exact same speed as the wheels at any given time.There is no wind at all in any direction.Can the plane take off?

 

[Chythar]

This is way off topic for this forum but I had to do it ,sorry admin.I got this off of another forum I belong to and take no credit for the question.I was the only one to get this right and it really is a tricky question.Ill post the link to the forums afterwords if anyones intrested.

A plane is sitting on a conveyor belt that covers the entire runway.The conveyor belt spins in reverse the exact same speed as the wheels at any given time.There is no wind at all in any direction.Can the plane take off?

Sure. The takeoff thrust actually comes from the jets, not the wheels. So the plane will pick up speed and take off no matter what speed or direction the wheels are moving in. Now, what condition the landing gear will be in after this little exercise is anybody's guess.

 

[1TallMF]

I would have to say yes, it will take off as usual. Assuming the friction in the wheels is negligible, this eliminates one factor from the system, leaving only the thrust of the engines on the surrounding atmosphere. The plane will take off as normal only the wheels will be spinning twice as fast as normal at all times (assuming they survive those rpm's)

 

[Blackened302]

think you'RE smart?

hehehe

i would say no--no wind, no lift. no lift, no fly.

 

[Therian]

VTOL

 

[WhiteStallionGT]

Yup, I'm with Paul. No wind = no way a plane can get off the ground.

 

[blksn955.o]

I agree, the lift comes from the air moving around the wings.

Planes do have a stall speed that if they dont keep up they will fall.

Now with diff. math....ANYTHING is possible. What is it a humming bird cannot fly by some physics...yet it does.

 

[Zero Signal]

Yeah I'm with Cythar. Planes rely on thrust, the wheels don't do any work, so the plane can take off. Furthermore, no matter how fast the plan is moving, the wheels will be moving at the same rate as the conveyor since they're coupled no matter what.

I have a better one. . .

Say you wrap a rope around the earth (lets say the circumference is 27,000 miles). Take that same rope and add 10 feet to it then wrap it around the earth again. If the distance from the rope to the earth's surface is constant and equidistant, WHAT would it be?

This is best in person whith your friends and tell them to do it in their head. Otherwise you guys will all break out the geometry. But the answer is pretty cool.

 

[pleasehelp]

It cannot take off. If you are talking about as soon as the plane starts moving and so does the belt and matches the thrust, meaning the plane will stay stationary it will not go anywhere. And if it's not moving it cannot create LIFT<---key word. I don't think it matters if there is no wind or not. So it would stay there stationary with the wheels spinning. Which there is nothing that makes the wheels turn except for thrust pushing the plane but it is being canceled out by the conveyor belt.

 

[69clark]

I say no but I'm also dumb so don't expect much!

 

[94venom5.0]

It cannot take off. If you are talking about as soon as the plane starts moving and so does the belt and matches the thrust, meaning the plane will stay stationary it will not go anywhere. And if it's not moving it cannot create LIFT<---key word. I don't think it matters if there is no wind or not. So it would stay there stationary with the wheels spinning. Which there is nothing that makes the wheels turn except for thrust pushing the plane but it is being canceled out by the conveyor belt.

i agree, no movement or wind = no lift....but im really not that smart i just quoted the guy..

 

[SeventyMach1]

Yes. Simply turn the conveyor belt off ..... that way you don't even have to think about it, lol.



Seriously ..... I don't think it can take off. If there was wind .... or some form of air motion, it could take off. But since there is no wind, the plane won't get the lift it needs to take off.



BTW, pleasehelp, I see what you're saying about the wind not really being a factor .... and I agree. But the plane COULD actually get it's lift if there was some nice winds. Usually they make their own wind by thrusting forward .... but not in this case.

 

[Zero Signal]

The fact is the plane's movement is COMPLETELY independent of what the wheels are doing. The wheels don't DO anything other than give the plan something to roll on while the thrust pushes it. How about a lesson in statics to prove that the plane will move forward as normal.



View attachment 467124

 

[Stangster5.0]

,this is getting as good as it did in the other forum.I should have made this a poll,I will post the answer when the thread starts dying down.

 

[95WhiteVenom]

On the belt that plane would move along as if it were normally taking off and produce thrust from the engines but without the WIND RESISTANCE against the wings the thrust can only propel the plane foward not up.

 

[GRGT1994]

The question has already been answered correctly in this thread. In fact this question has been posted here before.

In short, yes it will take off. Planes move forward by engine thrust, not by driven wheels. So it makes no difference what is happening beneath the tires (conveyor, floating stationary on a river, etc.)

The question attempts to conflate an impact from the conveyor on the plane, but there is none. Even if the plane were moving backwards on a huge conveyor, the engines could still thrust the plane so that it first slows it's reverse speed, then eventually comes to a halt (relative to the ground and objects not on the conveyor), then the engines continue thrusting the plane to takeoff speed moving forward (again regardless of the rearward speed of the conveyor).

The comment about there being no wind is a red herring. It's not that there is no air, nor is it that the plane cannot create lift (by forward motion), just that there is NO wind (read the question again). Now if the question posed that there WAS wind, and that wind was a substantial tail wind, then that could impact the ability of the plane to take off. But with a long enough runway to accelerate, a plane could take off (theoretically, ignoring turbulence) even with a 1000 mph tailwind. A plane creates its own "wind" for lift by moving forward, and it can still do that on this huge conveyor.

Remember, the conveyor exerts very little rearward force on the plane (only friction on the wheel bearings). But planes land and take off at high speed, so their wheel bearing are designed to operate a high speed. Hence, it would take an incredibly fast conveyor to exert enough rearward force to stop the forward acceleration of the plane. But the question does not mention the speed of the conveyor (mostly because the conveyor is another red herring and is essentially meaningless).

Simple eh?

 

[BlueOvalStangGT]

think you'RE smart?

 

[BlueOvalStangGT]

It doesn't matter what the conveyor belt is doing because the airplane's energy is acting on the air, not the belt. I had better luck simplifying the problem like so: imagine instead of a plane, you've got a rocket with wheels sitting on that belt. When that rocket fires, it's eventually going to rocket off the end of that belt...which means that it doesn't remain stationary to the ground and if it had wings, it would fly.


The plane gets its lift via the bernoulli effect. This has to do with wing shape and its interaction with air moving rapidly past. If the plane has no motion relative to the wind, there will bo no lift to force the plane up. That plane is going nowhere fast. Kind of.

Thrust acts accordingly to Newtons Third Law of Motion - every action has an equal and opposite reaction. In the case of an aircraft, the reaction of the engines is that of forward motion, against whatever medium it is stationary. But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.




I just googled your question and found that.

 

[BlueOvalStangGT]

Say you wrap a rope around the earth (lets say the circumference is 27,000 miles). Take that same rope and add 10 feet to it then wrap it around the earth again. If the distance from the rope to the earth's surface is constant and equidistant, WHAT would it be?

What would what be? The rope is still a rope.....or do you mean how long is the rope? Would it be 27,000 miles and ten feet?

 

[mootang]

No it will not take off because there will be no lift!!

since the plane will be stationary there will be no wind to provide lift, therefor the plane can not possibly fly!