No, the thrust would push the plane 'forwards' but the treadmill would turn at an equal speed in the opposite direction. The plane would not be able to move forward along the treadmill and so the air over the wings would not move relative to the plane and so would not generate lift.
why do you think (most) planes have to move forward to take off?
Thrust pushes against the atmosphere. So assuming the treadmill is the same length as a normal runway, the aircraft will accelerate until it's airspeed reaches takeoff speed, and it'll take off. It's wheels will be spinning madly because of the treadmill, but that has noting to do with the takeoff speed through the atmosphere.
Actually, there will probably boundary-layer effects from the treadmill, meaning the aircraft can take off at a lower speed, but ignore that.
Just which wheel size is best? And what tyres should I use on that size?
andrewh - Member
No, the thrust would push the plane 'forwards' but the treadmill would turn at an equal speed in the opposite direction. The plane would not be able to move forward along the treadmill and so the air over the wings would not move relative to the plane and so would not generate lift.
Of course it would. Planes don't need wheels to take off. The wheels have nothing to do with the power delivery of the engines! Planes are not cars they do not rely on drive from the wheels to move. The wheels could be going backwards at 500mph and all that the plane would suffer is some bearing drag.
why do you think (most) planes have to move forward to take off?
Because that is the most efficient way to take off and that's the direction they travel because of the engines thrust.
Are we seriously doing this?
Are we seriously doing this?
Whenever I read a response like andrewh's I think, good troll, then I realise he might be serious, and it makes me sad..
We are doing this but not necessarily seriously...
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however, yes the engines would push the plane 'forwards' but the treadmill would counteract that and it would remain stationary so no lift. The wheels have nothing to do with the engine, they are not conected in any way. However, the treadmill would cause them to turn in the wrong direction and stop the plane moving.
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you could in theory make it take off by putting a huge fan in front of it and blowing air over the wings, it would then take off from a standstill regardless of whether or not it was on a treadmill. If the treadmill worked do you not think aircraft carrier designers would have fitted them rather than enormous runways? Actually could a plane land on a treadmill?
However, the treadmill would cause them to turn in the wrong direction and stop the plane moving.
How, exactly? The wheels are free-turning, so how can they stop the plane moving?
If the treadmill worked do you not think aircraft carrier designers would have fitted them rather than enormous runways?
Airplanes do need enormous runways. Whether those runways are made out of tarmac, water, ice, ball bearings or a giant treadmill is irrelevant. As long as the runway is long enough for the aircraft to reach takeoff speed, it'll take off.
I think you think we're talking about vertical takeoff - we're not.
Mythbusters did this - here watch the plane take off then argue your case
A bit worrying that a (presumably) qualified pilot can be surprised by that.
however, yes the engines would push the plane 'forwards' but the treadmill would counteract that and it would remain stationary so no lift. The wheels have nothing to do with the engine, they are not conected in any way. However, the treadmill would cause them to turn in the wrong direction and stop the plane moving.
Put a skateboard on a treadmill. Push the skateboard forward. What happens?
he is not a physicist though is he
How many racing drivers could explain the internal combustion engine
I suppose - I'd hope he'd have a better understanding of thrust vs. drag, though.
I'm not really sure how this would take off with or without a conveyor belt
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My favourite piece of esoteric Stw knowledge was a when forumer asked an obscure lift (as in elevator) related question. STW did not disappoint.
Reading all these comments, I'm guessing the weather must be pretty rubbish in the uk just now?
My favourite piece of esoteric Stw knowledge was a when forumer asked an obscure lift (as in elevator) related question. STW did not disappoint.
My first channelling of the STW-foo I wanted to know the hole size and pitch of the perforated metal sheets that are used on the gantries over the M25. Within a couple of hours I had the email address of the bloke that had designed them.
What is a concrete poker actually for
It vibrates the wet concrete which makes any trapped air come to the surface which reduces voids increasing strength. It also helps the concrete flow into tight nooks and crannies and between the reinforcing.
HTH
🙂
Reading all these comments, I'm guessing the weather must be pretty rubbish in the uk just now?
It's about 20 degrees and they're all wilting in darkened rooms
Seems to me that folksmhaven't been clear about the role of the conveyor.
Imtought the whole point was that it kept the plane stationary
Imtought the whole point was that it kept the plane stationary
But how would it do that? Unless you run it really, really fast so the wheel drag becomes significant, the speed of the treadmill doesn't matter.
The same way a treadmill keeps,you stationary when you are running on it.
That's only because your legs are driven - your cant run infinitely fast, and if you stop running you fall off. Wheels can rotate as fast as you like.
So at what speed are people assuming the conveyoris running?
Okay, a thought experiment:
Imagine an airplane on a treadmill, with engines under full thrust. The treadmill can be rotating as fast as you like.
Now imagine you put wheels on that treadmill - so the airplane is on the treadmill, and the treadmill is on wheels. Wat happens?
What happens if you bolt the airplane to the treadmill frame?
Ben DR mungus be trolling
He be many things but dumb aint one of them
So at what speed are people assuming the conveyoris running?
Doesn't matter. There is no friction between the airplane and the treadmill, so it doesn't matter how fast or in which direction the treadmill is running.
No, i just thik the problem has never been clearly defined
Well, how would you define it? If the speed of the treadmill doesn't matter, the you can define it however you like, and it'll still have no effect on the result.
How would i define it? Depends on the point i'm trying to make. What assumptions are being made. Seems to be the frictionless wheels which cause the issue
Okay, they don't have to be frictionless - but now fast would the treadmill have to be going for the friction to be high enough to match the takeoff thrust of the engines? That's a lot of drag.
Okay,I'll accept that, if the treadmill is going at 1,000,000mph, the aircraft won't take off - because the wheels will explode.
Yeah, i guess it is the conflation of the questions. Would a non whell driven vehicle move forward on a treadmill. If that bit can be ascertained,as it can be, then the question about flight is trivial
Okay, here's a similar example. Imagine a bowling lane - you bowl a ball down the lane, it rolls to the end and hits the pins.
Now replace the lane with a treadmill - what happens if you try to bowl the ball down the treadmill?
It'll still roll happily along, won't it? It won't just stop dead.
No, i understand that bit, the bowling ball would work much like the roll a penny machines in arcades, they roll but stay in position until they slow down then fall over
Really? If you throw the ball forward onto the treadmill, it'll slow down until it's rotating just fast enough to exactly match the speed of the treadmill?
How does a bowling ball know how fast the treadmill is going?
Have you seen the roll a penny machines? The bowling ball would either move forwards or backwards on the conveyor, depend on its kinetic energy / angular momentum. The penny roller has the belt matched to the average speed of the coin
Okay, let's put some sums to it:
Say the treadmill is running at 1m/s. You bowl a 3kg ball at 2m/s. so the bowling ball has kinetic energy of 6J.
But if the ball becomes stationary on the treadmill, what happens to that energy? It's not gone into the treadmill - the treadmill is still going at the same speed. What's happened to it?
But your model does not have the ball rotating, the 6J is sliding
Okay, imagine you roll the ball instead of bowling it - like those ramps they use for kids. Now it's rolling - same difference.
Sure, but the energy is not 6J, you have rotational kinetic energy too
You do. So you go from 6J of angular kinetic energy and x rotational kinetic energy to zero angular kinetic energy and still x rotational kinetic energy. You've still lost the energy somewhere.
The same place you lose it when you roll a ball along a flat surface.
Are you aying that if you roll a ball down a slope and another down a sloed conveyor, the would both follow the same time- path?
you could in theory make it take off by putting a huge fan in front of it and blowing air over the wings, it would then take off from a standstill regardless of whether or not it was on a treadmill.
You could almost do that with a Feiseler Storch, 30m take-off with no head-wind:
https://en.wikipedia.org/wiki/Fieseler_Fi_156
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Sorry, you can't see the treadmill it's just taken off from...
Are you aying that if you roll a ball down a slope and another down a sloed conveyor, the would both follow the same time- path?
No, because they'd have a different angular momentum.
But actually that's a really good example - if you have the treadmill at an angle, will the bowling ball roll off the end?
It will eventaully, in fact you would need to continue to increase the speed of the onveyor just to keep the ball in place
Okay, now do the same thought experiment with something that has minimal angular momentum - a skateboard, say.
So imagine a skateboard on a sloped treadmill - will it roll off the end?
(Obviously there's the limiting case, as with the airplane, where the treadmill runs at 1,000,000mph and everyone bursts into flame)