[Closed] What is this aircraft on a conveyor belt that people often quote?

Firstly, the treadmill only moves if the aircraft, or it's wheels, depending on the question, moves... so, a stationary aircraft would be sat on a stationary treadmill.

Oh. I thought we had a powered one.

Funky, I dont believe it is possible in theory. Please see earlier post. What I do think "might" be possible is due to how a prop works, ie accelerating a cone of air. It "might" be possible that with a high lift wing this cone of air may be enough to generate the required lift due to airspeed over a portion of the wing whilst drag on the rest of the aircraft keeps the groundspeed(speed on the conveyor) to zero.

if that makes sense

This is an amusing thread, [i]Even though[/i] I am far from sure who is taking the mickey and who doesn't realise... There appears to be an element of double bluffing. Reminds me a little of Mornington Crescent... Love it.

Oh god noooooo...

uphillcursing... it has nothing to do with that. The way the aircraft moves forwards is by forcing air backwards, either by the use of a prop, or a jet. The wheels are merely there to reduce the coefficient of friction between the fuselage and the ground. If the wheels provided any motive force then how does an areoplane fly once it leaves the ground?

To nip it in the bud... Yes it can, as the engines provide the thrust not the wheels, but the treadmill would have to be as long as a normal runway. People think of it as gaining pace on the spot and being able to take off in no space, which is bollocks, the airspeed at take off would be identical, the wheels would just be going rather faster.

Couldn't we just lock the thread after this?

I'm pretty good at mechanical, dynamical, type physics and maths. This is what I believe would happen. I've talked to a pilot, and he confirmed my assumptions.

Not sure this really proves anything as I think the plane was going faster than the belt when it took off, it was definately moving forwards before it left the ground.
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Scuzz, an infinately long treadmill? Then you would be right. However most, maybe even all, treadmills are not infinately long. I was assuming that it would be about the length of the plane, which is much realistic 😉

Another thought, as the plane accelerate does the treadmill accelerate to match? If not all the plane has to do is out-accelerate the treadmill. If the treadmill is at a constant speed then Realman and whoever he is quoting are correct, but I think they have answered the wrong question.

Shirley the most important question in all of this is what tyres for the conveyer belt

andrewh - Member
Another thought, as the plane accelerate does the treadmill accelerate to match? If not all the plane has to do is out-accelerate the treadmill. If the treadmill is at a constant speed then Realman and whoever he is quoting are correct, but I think they have answered the wrong question.

I would have thought that the aircraft size was critical, you would need something Bomber size

Surely it also depends on the viscosity of air. If it was abnormally viscous then the conveyor would drag it backwards (or was it forwards?) which might or might not affect the air speed relative to the wing.

Funky.... Agree totally. What I am trying, and failing it seems to say . Is that to achieve any forward motion there has to be a force exerted by the prop. This is a force localised behind the diameter of the prop. If the diameter of the prop extends to cover a length of wing then this section will have airflow and therefore lift. The rest of the wing will not experience any any airflow and therefore produce no lift. given that conveyor keeps the aircraft stationary relative to a point on the ground.

Will the amount of airflow ever be big enough to let the aircraft take off? I think this may depend on the diameter of the prop. (maybe)

Am i dreaming? Is this really the nightmare returning to haunt me again?

Someone please make it stop!

Noooooooo.....

*deep breaths*

What you seem to be trying to answer is, can an aircraft ever take off will no forward speed, just the effect of the propwash over the wings. I'm fairly sure the answer to that question would be no.

But that is not the situation here.

There is nothing stopping the prop pulling the aircraft forwards. The treadmill is just a distraction.

Unless there is some way for the speed of the treadmill to influence the aircraft, which has non-driven, freely-spinning wheels, then there is no way for the treadmill to stop an aircraft taking off.

Uphillcursing, are you being serious? Lol

Beats a "what tyres for XXX " thread if nothing else 😉

Beats a "what tyres for XXX " thread if nothing else

we haven't even started on the 'what tyres for conveyor belts'question yet...

Conti Vert Pros obviously...

Next!

It has already been asked.
But not answerd.
Nobby nics for general all-round treadmills.
Do they do them in 42x23" folding?
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[EDIT] Funky's answer is better.

Well am I the only one wondering if it comes with a crown race?

uphillcursing - Member

Will the amount of airflow ever be big enough to let the aircraft take off? I think this may depend on the diameter of the prop. (maybe)

Surely it also depends on the viscosity of air. If it was abnormally viscous then the conveyor would drag it backwards (or was it forwards?) which might or might not affect the air speed relative to the wing.

I may have made it all up, though.

Noooooooooooooooooooooooooooooooooo

Scuzz, could we experiment with a hyrofoil and an infinity pool to test the theory by using something more viscous than air? Would the principle be the same?
Do they make hydrofoils with a prop at the front?

😛

Right off to bed. Might try and dig out a text book from the attic tomorrow.

Same principle, we'd need an impellor powered submarine shaped like a plane with a hydrofoil, and a large pump system to simulate the forward airflow the plane would generate from thrust and a sheet of plywood to simulate the treadmill surface such that boundary layer viscous effects could be taken into account!

There needs to be a whole new definition for people like you lot. Troll is wrong, as it implies nastiness and a 'victim'. You lot know exactly what you are doing, and you derive an almost perverse pleasure from it. I shall call you gnomes, and I require you all to sign the gnome offenders register at once. 😆

@ the OP, yes to the first, but that depends on when you joined, and no to the second question, because I can't be arsed.
HTH.

[img] [/img]
No reference points to gauge speed but doesn't look like it's going very quickly.
Whole tribe of gnomes over on the stupid headset question thread.

What if the treadmill was travelling at almost the speed of light?

Not sure. Depends what the chaps at CERN find, they may be able to get the plane to go a bit quicker than that (once they have found a way of scaling it up from one nuetrino).
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BTW Scuzz, I have added your last post to my purple book of silly quotes. No one in the whole of history has ever said that sentance before.

[img] http://i93.photobucket.com/albums/l41/xeroate/plane.jp g" target="_blank">http://i93.photobucket.com/albums/l41/xeroate/plane.jp g"/> [/img]
Can't quite make out treadmill from this angle.

as tthew hints at with Thrust SSC on the treadmill.... the jet engine is pushing against the air that it piles up behind itself

the wheels just allow the thrust power to used as efficiently as possible

imagine thrust lying on the ground dragging itself along on its belly, it could still move it'd just need more power* to counteract the chassis/ground friction
- Or lying on the treadmill pushing against the direction of the travel, needs much more power still
- but add wheels to thrust and the wheels and bearings allow the treadmill resistance to be nullified, the wheels can spin as fast as they want as long as the bearings don't pop

*trademark J Clarkson

[img] [/img]

Is the treadmill on a gradient?

Its all to do with the inverse square law.

Treadmill makes very little difference since planes taking off are all about airspeed and not groundspeed. The planes propellor or jet push against the air to get going and not the ground. A flat surface with little friction (like a treadmill) has little impact on the planes take off roll. A rough surface with lots of fricion such as long wet grass would have a big impact in preventing the plane achieving flying speed.

In a car it would be different since it is actually the wheels touching the ground that drive the car forward.

The aircraft carrier example is also rubbish since the planes always take off towards the direction that the carrier is moving. This gives the planes say a 20knt headwind to work with. This means that if their flying airspeed is 200knt then the plane only needs to be doing 180knt groundspeed when it leaves the end of the runway to acheive the 200knt airspeed.

Planes would never take off when the carrier is reversing. Never good airmanship to take off with a tailwind. A tailwind does not impact on the airspeed needed to get flying (in otherwords the airspeed would still need to be 200knt) - it just means that the time to accelerate to 200knt would be greater, hence needing a much longer longer runway. For example of the carrier was reversing at 20knt then the groundspeed needed to acheive a 200knt airspeed would be 220knt and not 180knt as in the previous example.

Hope that makes sense.

Well, if the Ref says it can take off, then it can take off, no arguing surely !!

🙁

Treadmill makes very little difference since planes taking off are all about airspeed and not groundspeed.

But until the plane is in the air, then groundspeed and airspeed are the same, aren't they? If the treadmill/conveyor belt keeps up with the thrust, as it moves the plane, through its wheels, then the plane will stand still and not take off. There.

EDIT: hang on, that's not right. Oh dear . . . 🙁

Please tell me you are all trolling?

Aircraft use their engines to push the [b]AIR[/b] to move, it has nothing to do with wheels, treadmills or whether there are brackets in the equation.

If the treadmill matches the planes speed, then the only difference to conventional take-off is that the aircrafts wheels will be travelling twice as fast.

What if the wings are upside down?

I refer you all to my previous post, not trolling, but you have been gnomeslapped, good and proper.

If you read the original question (as explaine by druidh way back at the start). It has everything to do with the speed of the wheels and the treadmill. 😉

Again two versions of the question and peoples inability to read is what keeps this thread going and going.

You lot have no idea how to do proper physics!

To start, let's assume the plane and treadmill are spheres in a vacuum...

What if the treadmill was going backwards?