Plane on a treadmill...

[Nick]

But it is connected to the ground, thats the point.

Well, no, it isn't. It's in contact with the ground which isn't the same thing.

The speed of the treadmill isn't constant, it changes to match the thrust of the plane (and hence the speed of the wheels) and so can't be ignored.

Yes it can, as you'll see in a minute...

The wheels spinning and the thrust of the engines are not separate - where do the wheels get the force to spin? The engines.

No, the engines are not connected to the wheels. All any aircraft engine does is move air faster out the back... be it a prop or a jet. All aircraft wheels are unpowered, freewheeling things that stop the paint on the belly of the plane rubbing off on the runway.

So what's turning the wheels then? The treadmill.

Think about it, if the treadmill was spinning faster than the thrust of the engines, the plane would move backwards. If the thrust of the engines was faster than the speed of the treadmill, the plane would move forwards.

True to some extent. If you could actually build a dirty great treadmill and stick a 747 on it, then start up the treadmill, friction and momentum would see the 747 move back along the treadmill, the wheels not turning. However, the thrust from the engines is a separate force and, if the wheels are just freewheeling, it makes no odds how fast the treadmill goes or the wheels spin, the force from the engines will still propel the plane forwards, relative to a point stationary to both the treadmill and the plane.

The problems states than the treadmill matches the speed of the wheels. The wheels aren't powered by anything other than the thrust of the engines and so the force produced by the engines is matched by the force produced by the treadmill....

Again, the wheels aren't powered by anything at all... they turn because of the friction between them and the relative speed of the object they're attached to.

Imagine a landing plane... the wheels aren;t spinning as it comes into touch down but then they spin like fury as the plane lands... that plane could land on ice and the wheels would skid... perhaps even lock up if the pilot applies the breaks... does the plane instantly stop moving? No. That's because the relationship between the wheels and the plane and the wheels and the surface are two different things, which is why the wheels are freespinning...

As someone said earlier, imagine there are no wheels. In fact, how about imagining you've got the worlds first flying hovercraft... the speed of the wheels over the treamill and the speed of the treadmill are unaffected by the thrust of the engines... (other than to make the wheels spin like billy-o...)

[redsky009]

sorry, silly Firefox, double posting

[redsky009]

Why is there a hand pushing the plane back? The treadmill exerts zero force on the plane because the (frictionless) wheels freely rotate. All that happens is the wheels spin faster.

If it was frictionless, the wheels wouldn't rotate at all, the treadmill would spin and the wheels would remain stationary.

Think of it this way, a car is travelling at 100 mph: its engine exerts a force of x N forwards, the road exerts a force of exactly x N on the car - The forces balance, the car is moving, but not accelerating. In order for the plane to take off, it needs to exert more force than the treadmill exerts back, but this wont happen as the treamill (unlike a road) changes its speed and thus the force to match the thrust of the plane

[yamangman]

Ahhh, but the F/A-18 hornet has a powered nosewheel

[autopilot]

If it was frictionless, the wheels wouldn't rotate at all, the treadmill would spin and the wheels would remain stationary.

People are talking about the bearings in the wheel, not the wheels rubber against the surface of the treadmill.

[redsky009]

So what's turning the wheels then? The treadmill.

So many things to address, so little time

Just plane (I'll get my coats) wrong - the treadmill matches the speed of the wheels, hence if the wheels weren't turing, the treadmill wouldn't make them turn as it wouldn't be turning either.

The fact that the wheels are freespinning is all well and good, but the only reason the wheels are turning at all is the friction with the treadmill surface and the force from the thrust of the engines to which they are attached, (albeit indirectly). If they weren't attched the wheels would stick to the treadmill and the engines would go forward and leave their little wheels behind.

anyway, until someone builds one (myth busters anyone?) to on small scale for e.g. the sceptics will never beleive

[BenW]

The treadmill does not move the air around it. Therefore the air around the treadmill (And the plane) is just the same as it would be on a normal tarmac runway.

Planes work by moving the air around them. Ony the treadmill the air is the same as air on a stationary runway.

The wheels are disconnected to the engine so are free to spin at any speed.

A plane on a treadmill is identical to a plane on a runway.

[redsky009]

People are talking about the bearings in the wheel, not the wheels rubber against the surface of the treadmill.

Ay, but ball bearings or not the wheels are physically attached to the plane. If you pushed the wheels on a frictionless surfcae, the plane would move.

[BenW]

Ay, but ball bearings or not the wheels are physically attached to the plane. If you pushed the wheels on a frictionless surfcae, the plane would move.

No it wouldn't, the wheel would spin on the surface

[redsky009]

No it wouldn't, the wheel would spin on the surface

sorry, should ahve said, if you exerted horizontal force on the wheel, the plane would move.

Wine time play nicely now, i hope to have a hangover in the morning

[Skyrail]

So wait a minute, the plane is weightless or there is no gravity? these planes weigh a hell of a lot and so the wheels aren't just going to spin freely, you all talking about it as if the wheels are just touching the treadmill so they just spin, friction and the weight combined means that the wheels are effective to a certain point until the speed of the plane/treadmill overcomes the wheels friction and it's own weight meaning that there is no longer anything pulling it back. I think I don't know what I am talking about :F maybe just a load of rubbish, but I've gone back on myself lol.

So the plane wouldn't take off for a while, that's all

[redsky009]

So wait a minute, the plane is weightless or there is no gravity? these planes weigh a hell of a lot and so the wheels aren't just going to spin freely, you all talking about it as if the wheels are just touching the treadmill so they just spin, friction and the weight combined means that the wheels are effective to a certain point until the speed of the plane/treadmill overcomes the wheels friction and it's own weight meaning that there is no longer anything pulling it back. I think I don't know what I am talking about :F maybe just a load of rubbish, but I've gone back on myself lol.

So the plane wouldn't take off for a while, that's all

Almost right, except in this situation, the force exerted by the ground/treadmill is changing with the force of the plane's engines, so the plane would never overcome this resistance and never move forward.

[Skyrail]

hmm, good point, then again if it did get to the right speed a matter of things probably would of happened including ran out of fuel, engines overheated, reached it's terminal velocity yadayada

[JPreston]

So wait a minute, the plane is weightless or there is no gravity? these planes weigh a hell of a lot and so the wheels aren't just going to spin freely, you all talking about it as if the wheels are just touching the treadmill so they just spin, friction and the weight combined means that the wheels are effective to a certain point...

Noooo as posted above the tyres are perfectly grippy, there is 100% friction between the tyres and the treadmill, they work exactly as they should. The plane is of normal weight, gravity is normal, the wheel bearings are frictionless so the wheels are 100% efficient. Everything works exactly as it ideally should.

[Nick]

Right, I've got one word to solve all of this.


Helicopters.



Go away, find out how they fly (not how you THINK they fly but actually how they really do fly, ie, go a research and read), then come back and admit that either the plane will take off or helicopters cannot fly.

Go on, stop reading this post, go and Google.

[Skyrail]

Changed my mind again after discussing it with my dad, I keep on changing my mind too much, I'll stick with it won't move