Imagine a plane is sitting on a treadmill

so in conclusion...

the answer is...

Is that why there are no conveyor belts at John Lennon Airport?

Here, I got Mater to do a demo, note in this situation he has no forward force, only the small backward force due to the friction in his wheels. If his wheels were locked then of course the outcome would be totally different. If he had a jet engine on top then he would go forwards regardless of how hard or fast i pulled the paper out from under him. If you want the video pm me.

no it would go backwards! i say the plane remains in the same position! therefore not creating lift? i refuse to fly again until i know ican trust you lot.

must go great thread btw. dont realy care if im wrong or right tbh.

Just as the planes at John Lennon airport dont have wheels!

You can't go gideon, we're not finished with you yet!

As you well know you naughty minx the loss of one testicle would still leave me with two fully functioning ones.

If the conveyor belt is moving at 1000mph and the wheels are rotating at 2000mph then the aircraft will be moving w.r.t the air. The questions states (I think) that the plane and the conveyor belt are moving at the same speed, but the wheels will be rotating much faster.

So we've concluded no airspeed, no lift, and JE has three functioning testicles. Well done TT. It's a great day for science.

You told me that you had bet and lost them years ago.

sGb57 now do it slowly, your cars stays in the same place due to inertia. the plane is taxiing so starts from 0. and the whole system works in tandem. sorry did toms push pencil paper thingie and i got the same result as you did...

wheel i have to go. i will be using a hovering thermo nuclear hoverpad. now explain those physicy, cos you guys are donig well...

i wish discovery or the beeb would do this for real... we could all meet and be geeky.

Has your missus given them back yet, then?

Hey if one of you would hit the emergency stop button on the belt I bet you have a hell of a take off ;-)

ok so what about landing?

could you land a plane on a moving conveyor belt so that we could have really small runways?

*clears throat*

*decides not to say anything*

Hey, I told you I had just scanned the thread, couldn't be arsed to trawl through all your geeky nonsense

What slows a plane down when it lands?

The airbrakes.

Case closed m'lud.

Hmmmmm... I think that I've recognized a flaw in my logic. Of course, the conveyor is designed to match the speed of the PLANE, and not of the speed of the WHEELS at the point they touch the conveyor!!!

So, I change my answer: the plane will take off, assuming that the engines can produce enough thrust to negate the speed of the conveyor itself.

Simply because the rolling friction of your pencil relative to the pencils mass is enough to accelerate it with the paper at such a slow speed.

Yes of course, and now I am giving him a gentle breeze from behind and he zooms off forwards. No matter how fast or hard I pull the paper I cannot compete with the gentle wind from behind, now imagine a jet engine.

Or maybe I'm just talking shit and have no idea what's right... ???

Fuck, I need a beer...

The correct answer is that no enough information is given. The issue is lift and as DW hasn't said what the airspeed was (i.e. to generate enough lift). Yes, the plane could take off if it also had hurricane force headwinds.

The question had all the information necessary.

You could, however, add that its a still day but that would not affect the answer.

You could also say the runway would be long enough for the plane to take off normally, but thats pretty well assumed as most planes fly to/from airports with runways that are long enough.

You could say that the treadmill moves at the same airspeed as the plane, but it would make no difference.

You could say that the treadmill moves at the same groundspeed as the plane, but it would make no difference.
(the above two statements are identical anyway if there is no wind anyway)

The plane will take off

@ Bumpy

What makes a plane go forwards? Clue: not its wheels.

Bumpy's post is as much use as a 3rd testicle.

What, "handy if you lose the other two"?

Actually Bumpy is right. Read the DW post about flying a plane backwards. It all depends on where to and how fast the air is moving.

If you assume the air is staying still relative to the ground (in other words there's no wind) the plane will take off.

I'm off for a while. Have fun.

If the air is staying still relative to the ground, and the plane is staying still relative to the ground (the treadmill is taking care of that by definition in the question), then the plane is staying still relative to the air. So it won't take off.

That's the point genie - the treadmill is NOT taking care of it by definition.

EDIT: Assuming the wheels don't lock, and assuming they are normally attached to the aircraft (i.e. can travel freely backwards and forwards), how is any force, whatsoever, exerted by the treadmill on the aeroplane? On the other hand the aeroplane IS exerting force on it surroundings by way of its jet engines, which will allow it to move forward normally.

The question is doing nothing of the sort. Re-think your logic

Right, I am off out now as well. I hope this comes up in the Arc Quiz

I'm assuming the speed of the plane means the ground speed of the plane.

Ground speed, air speed, its all the same if there is no wind. "Treadmill speed" however is a different factor here and largely irrelevant.

BYE!!!

Actually, you're right. I meant "treadmill speed", not ground speed. But it won't get off the ground anyways. If you have the treadmill run backwards at the ground speed of the plane (not it's treadmill speed), by definition you have a stable solution only at 0 ground speed, because for any non-0 ground speed the treadmill will act to counteract it (we're assuming here zero-latency dynamics of the treadmill, right?).

So in any case - zero ground speed, zero air speed.

Unfortunately though for you, the power of a jet engine far outweighs any bearing friction in the wheels, so it is very easy for the plane to accelerate away. There is no way you can stop a plane from getting away by tugging the "ground" back from under it, no matter how hard or fast you try.

Oh, I'm not that unfortunate about the plane, if it gets off the ground or not. I still think it doesn't, because the only thing we know about the treadmill is that it matches the speed of the airplane, which means it keeps it at 0 ground speed.

If the conveyor moves forward(same speed as the airplane) the only difference would be that wheels won't spin. Take off still happens

The plane is connected to the treadmill by wheels that are completely free to rotate though, so even if the treadmill is running backwards, it doesn't mean the plane's ground speed will be affected.

Plane will not take off. Airplane engines just do not have enough thrust to overcome the weight of the airplane and the need for lift. If they could, a plane could take off without a runway straight into the air. Normal planes are not built that way, a rocket propelled one maybe, but a commercial airplane not. An airplane has to reach a certain forward speed, not thrust, to achieve lift.

This is too funny. I hope you're enjoying it DW.

I'm having an absolute blast.

That is a clue!!!

I have a fairly academic maths / physics background and was originally in the "off-course its gonna take-off, dumbass" school of thought.

However...(change of mind)...I was about to say that it wouldnt take off, but have realised the crucial flaw - the engines are pushing against the air, not the moving treadmill.

If the engines were driving wheels sitting on the moving treadmill then, correct, the airplane itself would not budge an inch as any forward propulsion in the aircraft wheels would be offset by the reverse motion of the moving treadmill.

However, the thrust is coming from the engines pushing against still air and therefore the plane will move forward relative to the air at (say X mph) - the movement of the treadmill is irrelevant

The movement of the treadmill at X mph in the opposite direction only means that the airplane wheels will be rotating at 2X. However, the aircraft still takes off at its normal take-off velocity

Q.E.D.

...which was much more succiently expressed by Tom17 at about 3.34pm today...

the rest of you are wrong with a big W

... Never mind..

Because the planes are held to the ground either by brakes or straps. If there were no straps and the brakes were off the plane would move.

Anyone who still thinks the plane won't take off, go back and read all the posts, paying special attention to these ones :-D

If there was no friction between the wheels and the plane, and the engines were not on, then the plane would not move, only the wheels would spin. So, if the engines are then turned on, there is resultant force which would move the plane forwards. The only difference here is that there is a small amount of friction between the wheels and the plane, which means the forward force is marginally less, but still great enough to move the plane forwards. If the plane moves forward, air flows over/under the wings creating lift and so plane takes off.

OF COURSE THE DAMN THING TAKES OFF! BLOODY HELLLLLLLLLLLLL! 13 PAGES!!