andrewh… well, you have the conservation of momentum just about there… kinda..

Now you just need to understand that it’s got pretty much bog all to do with this, as the aircraft has a source of forward thrust that does not rely on the ground one little bit. The ground can be doing what the hell it likes… moving backwards or forwards, the plane will still take off…

njee20 – Member
Of course it can, BECAUSE THE WHEELS ARE NOT POWERED.

Right… toy car, on a conveyor belt. Can you push it forward, even if the conveyor belt is moving? Of course you can. That’s how the plane works.But if it’s a very big conveyor belt, then you’d be on it too, so you’d be moving backwards. Then, when you push the car forward the net motion would still be zero!

Haha! Well I know you’re trolling, so I’ll just ignore you!

Iit’s down to thrust and drag, the treadmill won’t have any effect on the aircraft as it’s not providing any friction at the wheels

It’s got nothing to do with friction at the wheels. thrust from the planes’s engine will make it faster but the treadmill speeds up to match.
Lets ignor the wheels for the sake of clarity. Imagine a fuslarge with a jet engine sitting on the treadmill. The thrust pushes it ‘forwards’ the treadmill ‘backwards’. However much thrust is generated the plane will not move as the treadmill sends it at an equal speed in the opposite direction. It can only take off it can out-accelerate the treadmill, which it can’t because the treadmill speeds up to match.
The question really is, can enough lift be generated by a stationary plane? I don’t know.

Sationary plane

Stationery plane

Aaaaaaaargh… you can’t ignore the wheels… the aircraft wouldn’t be able to take off irrespective of whether there was a treadmill or not without wheels (or equivalent)!

Nope, that’s it, you have to be trolling now.. *sticks fingers in ears* lalalalalalla

The question really is, can enough lift be generated by a stationary plane?

You’d want one of these, which could take advantage of the ground effect from the moving conveyor belt

And how is the treadmill resisting the thrust of the engines The wheels can spin freely regardless of any speed the treadmill is doing, Aerospce vehicles fly perfectly well without the need to generate lift ,the treadmill cannot counteract forward thrust produced by the expansion of the exhaust gasses unless the friction between the wheel on its bearing and landing gear is increased.

OK, lets have the wheels back on. It can’t move forward if the ground is moving at the same speedin the opposite direction. More thrut just makes the wheels turn faster (by speeding the whole plane up, not powering the wheels) and the treadmill speeds up in the opposite direction.
If “forward” speed = Nmph then the treadmill will move the other way at -Nmph and the plane will be static with the wheels spinning at 2Nmph

Oh dear god… *bangs head against a wall*

you would be better assuming that the fuselage is levitating magnetically, i.e. there’s no friction between it and the conveyor belt rather than imagining it just sitting on top.. (in which case it would not react as you describe anyway..)

If there is no friction then yes it would move forwards. But there is so it doesn’t.

so where do you choose to draw the line? how much friction is required?

But what if it was a plane on shopping trolley wheels and the conveyor belt was moving side on and it was made of ice and a South African was passing a ball out the window?

But you’re assuming friction increases with speed, which isnt the case. Imagine sitting on your bike on a treadmill and holding the sides of the treadmill. If you turn on the treadmill at 5mph you only need to hold on gentle to keep yourself in place (totally ignore the bike can be pedalled!!). You can pull youself forward with very little extra effort. Increase the treadmill to 50mph and you still only need to hold on with same force to remain stationary as friction is constant.

Take same situation with the plane – it would use only a very small proportion of its power to remain stationary, regardless of whether the treadmill was turning at 5mph or 500mph. That means that the rest of its thrust can be used for forward momentum, and as we all know – airspeed is what makes the plane fly…

Andrew you’re the only one who’s still not realised you’re talking crap! How long will it take?!

Isn’t this the 3rd time this topic has come up over the years?

[video]http://www.youtube.com/watch?v=bEyfHwDdXSg[/video]

Andrew,

In some respects you are right. If as the question sometimes states the treadmill matches the speed of the wheels then the plane will always have a ground speed of zero (where the ground is everything that is not on the treadmill) and so is unlikely to have any significant airspeed. In practice this is impossible to set up but like all good theoretical questions practical considerations don’t come into it. There was a joke above about considering perfect spheres in a vacuum. It’s that kind of thing and is the trick part of the question for those not paying attention.

However, there is another version of the question which leaves out the details about the speed of the wheels and instead refers to the speed of the plane. In this case the treadmill is an irrelevance as the wheels will just spin faster than the treadmill allowing the plane to move forwardand gain enough airspeed to take off.

jonba,

the wheels and conveyor are an irrelevance in both versions of the question. Thrust, an external force to the wheels and conveyor still acts upon the aircraft.
Assuming 0mph windspeed, the groundspeed of the plane (the speed of the conveyor) would be 2 x airspeed.

If you overtake the last person in a race, then you are in what position?

1st place – you’re lapping them.

If you overtake the last person in a race, then you are in what position?

Same as you were before, because you weren’t in the race.

Andrew you’re the only one who’s still not realised you’re talking crap! How long will it take?!

Probably depends how much encouragement we give him.

Isn’t this the 3rd 495th time this topic has come up over the years?

Yes, about right!

the wheels and conveyor are an irrelevance in both versions of the question. Thrust, an external force to the wheels and conveyor still acts upon the aircraft.
Assuming 0mph windspeed, the groundspeed of the plane (the speed of the conveyor) would be 2 x airspeed.

This. As said previously, if the conveyor belt is moving at the same speed as the plane then it’ll take off at 150mph as normal, but the wheels will be doing 300mph. It’s completely irrelevant.

andrewh is making me laugh.

😀

Quality, wether intentional or not.

I think njee bike on a treadmill was a good example.

If you stand by the side of a treadmill and lower a bike on to it. You wont feel any force pushing you backwards. As the wheels will turn.

I suppose it would theoretically be possible to run the treadmill so quickly that that enough friction builds up in the hubs that the wheels cant match the speed on the treadmill and then you would feel the backwards force.

Not trolling, but have a sneaking suspicion that I am being a bit dim somewhere…

In this case the treadmill is an irrelevance as the wheels will just spin faster than the treadmill allowing the plane to move forwardand gain enough airspeed to take off.

That is kind of the point. If the treadmill accelerates to match the speed of the wheels then it doesn’t move forwards and so gets no air-speed.

All the wheels do is stop the bottom of the plane getting scuffed so why would the speed of the treadmill have any effect on the plane taking off?

Must resist….

Can it take off IF the belt matches the speed of the wheels

is equivalent to

Can it take off with zero groundspeed

yes, it *could* easily take off, but the wheels would be spinning faster than the belt, which breaks the constraint (as happens in the vids).

Yes, its both stupid and impossible, but there you go.

Everyone else understood this from page 1 onwards…

“This. As said previously, if the conveyor belt is moving at the same speed as the plane then it’ll take off at 150mph as normal, but the wheels will be doing 300mph. It’s completely irrelevant.”

If conveyer belt is moving at 150, then the plane will be moving at 150 relative to the treadmill, the wheels at 150 again realative to the treadmill. Relative to fixed point on ground aircraft is not moving, no airflow, no lift. No ground effect as speed over groud is required (not speed on conveyer belt). Jeez, why is there even a debate on this!!? Conventional plane will not take off if forward thrust matches speed of conveyer belt. Plane needs airflow over wings to generate lift.

Thrust vectoring assets are very different as they can genertae their own lift.

To quote Scroobius Pip –

“I’ve seen the world; I’ve seen the good and the shitty bits;
And all I’ve got to say is god damn, y’all are **** idiots.”

😀 😀 😀 😀 😀

I thought we solved this last time by saying that we needed an enormous fan in front of the plane, rather than a conveyer belt?

dont make me find the old thread

Conveyor belt: designed to run in the direction of travel.
Treadmill: Designed to run against the direction of travel.

Basically the wheels and treadmill are an irrelevance: The way the plane picks up forward momentum is by pushing against the air pressure, not against the friction of the ground; the wheels are there to merely aid the movement of the plane, not to propel it. Therefore, the plane will take off regardless of what the treadmill is doing as the treadmill has no effect on the air pressure surrounding the plane.

As many others have said, the only effect the treadmill would have is to make the wheels spin faster than if the plane was taxiing on an ordinary runway.

Goddamn it druid, you bad bad man!

Here’s another way for wallace to look at it, just in case he’s not trolling.

The treadmill is stationary, the plane is stationary, the jets go on full thrust and it begins to accelerate. when it gets to 100mph, the treadmill suddenly switches on, instantaneously going at 100mph. what happens to the aircraft’s speed relative to the air around it and the non-treadmill ground? Does it carry on accelerating? Or suddenly stop or start to go backwards?

You can have the airstrip made up of a bunch of treadmills in a row, all going at different speeds forwards and backwards, the plane will accelerate over them. The tyres will be under a bit of strain, but the plane will still accelerate in relation to the air and the earth (not treadmill) until the airflow over the wings generates more lift than the weight of the plane.

Or:

Can a plan land on a treadmill? Or a conveyor belt?

I’m still not sure what the question is.

Bit late to this and I struggle with long sentences, if the plane can take off coz “it’s airspeed over the wings produced by the engines” then why don’t planes just sit on a short runway with their wheel brakes on give it some beans and take off from stationary? Could save a lot of money building the next airport.

The myth busters episode doesn’t seem right because the plane moved forwards, the “conveyor belt” was running backwards but the thrust from engines carried the plane forwards.

I’ll stick with my original “no it won’t” stance.

That’s the spirit!!

Nedrapier – I do not disagree with you. In your scenario it will still accelerate.

However, the scenario in question dictates that the belt will match the speed of the wheels, therefore speeding up, and the thrust increases, therefore the aircraft will stay stationery, with the thrust used up to keep it stationery. No flight.

On running treadmill, you generate no forward momentum, so if you jump up, you would not leap forward relative to ground.