Off topic - a little puzzle

This inoccuous little teaser has been doing the rounds on discussion forums everywhere, and almost without exception, causes heated debate.

Just thought I'd try it here....

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" A plane is on a runway that is made of a large conveyor belt. The plane starts up its engines and starts to move forward, but as it moves forward, the conveyor belt senses the speed of the plane's wheels and moves at exactly the same speed in the opposite direction. Can the plane take off???"

Yes. Done to death on Pistonheads, Skyline OC etc...

Yep - Skyline Owners forum. 16 pages, 300-something posts and over 2000 hits in 3 days.

Which camp are you in, Dave ? YES or NO

Yep - Skyline Owners forum. 16 pages, 300-something posts and over 2000 hits in 3 days.

Which camp are you in, Dave ? YES or NO

I just said above, yes.

Heres one for you...

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

The question is:

Will the helicopter take off or not?

Aeroplane nope - Helicopter yup.

Before anybody says Aeroplane no, just consider this alternative..

Imagine you put a roller skate on one foot, and attempt to put it on a non moving tread mill (but this treadmill will move in exactly the opposite direction and exact speed to your foot if you push your foot forward)

Do you honestly think you will never be able to push your leg forward, ever, like its forced up against an immovable brick wall?

Right - I'm on a treadmill, on a skateboard - what do I do next?

Right - I'm on a treadmill, on a skateboard - what do I do next?

Flap your arms...

OK - couple of large farts and I moved forward. It would appear that the friction that the skateboard wheels was not significant enough to overcome the massive thust that I produced and so I moved relative to the rest of the room. So I have to admit that my initial analysis was proven wrong by a controlled experiment. The plane would take off. The speed of the wheels and converyor belt is largely irrelevant.

If you think of it in reverse - if you started up the conveyor belt whilst the plane was stationary, would the plane immediately move backwards at the speed of the converyor? No - its little wheels would spin like the clappers and the plane would slowly build up speed. So the speed of the plane relative to the ground does not have to depend on the speed of the conveyor/wheels. Ah what a fool i've been - I;ll get me coat

Helicopter yup.

That wasnt a serious conundrum....

Here is one though...

http://www.youtube.com/watch?v=UXq8ixy-Dwo

Very good - thats cheered up a very dull afternoon

Is this a terrorist threat?

[Alpineandy]

The speed of the wheels and converyor belt is largely irrelevant.

So the speed of the plane relative to the ground does not have to depend on the speed of the conveyor/wheels.

A planes ability to take of is it's speed relative to the air, not the ground.
Air speed not ground speed. Could it get enough air across it's wings to generate lift?

The speed of the wheels and converyor belt is largely irrelevant.

So the speed of the plane relative to the ground does not have to depend on the speed of the conveyor/wheels.

A planes ability to take of is it's speed relative to the air, not the ground.
Air speed not ground speed. Could it get enough air across it's wings to generate lift?

I think Mich means the speed of the plane relevant to the ground (planet), ie if the plane is flying at 100mph, and a conveyer is going 100mph or the wheels are going 50mph makes do difference, its still 'flying' at 100mph..

In reality, as the wheels freely spin on the axels, and are not 'driven' by a motor/direct drive, the fuselage above being pushed by the jet engine doesnt really give a toss what direction the 'ground' is moving below...

Here's another angle that makes it easy to work out. Imagine the wheels are actually spheres that can move in ALL directions, and instead of the conveyor going the opposite direction to the plane, it goes sideways instead, at the exact same speed of the plane. Do you think once started the plane will travel in an exact 45 degree direction, or will thrust overcome it and it will eventually end up going more or less straight...