Will it take off?

Splog

Splog

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An oldie but could be fun to discuss :D


Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Can the plane take off?
 
Splog said:
An oldie but could be fun to discuss :D


Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Can the plane take off?
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No - it is the airflow over the wings that generates the lift. If the speed of the wheels / belt match then the airplane will remain stationary and there won't be any air passing over / under the wings.
 
Didn't they prove it would on mythbusters?
 
Because the thrust of the engines work on the air, not the wheels. So the wheel speed is irrelevant!
 
Gary said:
i wouldnt believe everything you see on mythbusters ;)
thats all i'm saying :)
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No worse than mods telling us something is afoot in forum discussion and then failing to follow through:):naughty:
 
Splog said:
An oldie but could be fun to discuss :D


Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Can the plane take off?
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hold on, i just read it again.

i thought you meant the plane is standing still whilst the conveyor turns the wheels.. is the plane actually moving? *confused*
 
Ramp up the thrust and hence the conveyor belt velocity, and the ground effect under the wings could achieve the desired result.

Then again, "happiness is vectored thrust". Is the plane a Harrier?
 
Gary said:
the conveyor will cause some air to pass over the wings, but not at the speed it needs to take off..

i wouldnt believe everything you see on mythbusters ;)
thats all i'm saying :)
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Sorry Gary but the plane will take off easily (y)
 
Gary said:
hold on, i just read it again.

i thought you meant the plane is standing still whilst the conveyor turns the wheels.. is the plane actually moving? *confused*
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The plane and conveyor belt are both still to start with, but as the plane fires up it's engines the conveyor runs at exactly the same speed as the aircraft wheels rotate but in the opposite direction ..
 
I've given this matter far too much thought and now my head aches.
 
Splog said:
The plane and conveyor belt are both still to start with, but as the plane fires up it's engines the conveyor runs at exactly the same speed as the aircraft wheels rotate but in the opposite direction ..
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ooooooooooooooooooooo

didnt realise it was under thrust.. :)

in that case YES.. did i get it right? did i?? LOL
 
If it does start to move though the Gov't will find a way to tax it.
 
sheddy said:
I've given this matter far too much thought and now my head aches.
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Gary said:
ooooooooooooooooooooo

didnt realise it was under thrust.. :)

in that case YES.. did i get it right? did i?? LOL
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:LOL: Yes you did get it right gary (y) but it did take you two attempts :naughty:
 
I am confused by the question. Is the plane stationary, like a person on a treadmill? Or is it effectively a huge treadmil the length of the runway that shoots the plane along the ground at great speed?
 
HuntingMartians said:
I am confused by the question. Is the plane stationary, like a person on a treadmill? Or is it effectively a huge treadmil the length of the runway that shoots the plane along the ground at great speed?
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It's a treadmill that will run and match exactly the speed of the aircraft wheels, much the same as a runner on a treadmill matching the speed of it, but vice versa.

Isn't this about 'lift'...? In order to fly, there needs to be enough air flow over the wings to generate lift. If any forward movement of the plane is countered exactly by the revers direction of the treadmill, then the plane doesn't physically move forward or backward in space, and thus there is no airflow over the wings and thus no lift.

With this explanation, the plane doesn't fly.

That said... I am still not convinced of my answer.
 
theMusicMan said:
It's a treadmill that will run and match exactly the speed of the aircraft wheels, much the same as a runner on a treadmill matching the speed of it, but vice versa.
Isn't this about 'lift'...? In order to fly, there needs to be enough air flow over the wings to generate lift. If any forward movement of the plane is countered exactly by the revers direction of the treadmill, then the plane doesn't physically move forward or backward in space, and thus there is no airflow over the wings and thus no lift.
With this explanation, the plane doesn't fly.
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I agree

theMusicMan said:
That said... I am still not convinced of my answer.
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Me neither
 
theMusicMan said:
It's a treadmill that will run and match exactly the speed of the aircraft wheels, much the same as a runner on a treadmill matching the speed of it, but vice versa.

Isn't this about 'lift'...? In order to fly, there needs to be enough air flow over the wings to generate lift. If any forward movement of the plane is countered exactly by the revers direction of the treadmill, then the plane doesn't physically move forward or backward in space, and thus there is no airflow over the wings and thus no lift.

With this explanation, the plane doesn't fly.
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That's what I said.
 
You're assuming the aircraft is powered along by the wheels, it's not. The thrust from the engines will move it forward regardless of how fast the wheels are turning under it.
 
As I said 1 hour ago!!
 
The conveyor belt will drag air under the aircraft, which could cause sufficient ground effect. But will the conveyor belt stop instantly it loses contact with the wheels? (Thus killing the ground effect.)

If it's a multi-engine prop plane, there'll be airflow over the wings. Jets too?
 
Consider this folks, and is why I remain non decided.

Place a car on a treadmill, brakes off, in neutral, turn the treadmill on... what would happen...?

Turn the treadmill on slowly and the car would probably move with the treadmill. Turn the treadmill on quickly thus overcoming the inertia of the car, and possibly the car would stay still in space, but the wheels would turn (assuming minimal friction etc)

With me so far...?

Crank the speed of the treadmill up and the car remains physically stationary, but the wheels turn at the same speed... come to a constant speed and we have the car not moving in space with the treadmill running, and the wheels turning.

Agreed...?
 
The experiment is flawed. For the conveyor belt to move the plane backwards to match the thrust of a jet engine there must be friction in the bearings on the plane wheels - if there's no friction the plane will not be slowed. The amount of energy that would have to be dissipated through the wheels by them spinning and converting the kinetic energy from the thrust into thermo dynamic energy through friction is immense - it's the amount of energy produced by the engines. The wheels will melt or catch fire very quickly.

In any case, if the plane doesn't move there can be no lift from air travelling over the wings so the plane can't take off.
 
the plane is moved by the engine be it a prop or a jet engine, which moves air the wheels are not powered, my take on it is that regardless of how fast the wheels spin the engines will try to drag the plane forwards, if the engines can overcome whatever resistance the conveyor belt imparts on the wheels then it will move forwards regardless and eventually take off, but it will not be in contact with the conveyor belt. whilst their will be an amount of air being moved about by the engine (and the air being moved by the conveyor) i dont think this would be enough to generate the lift required to take off.


unless of course the conveyor setup is part of a windtunnel setup where the air is also moved but then thats a completely different kettle of tuna
 
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onomatopoeia said:
The experiment is flawed. For the conveyor belt to move the plane backwards to match the thrust of a jet engine there must be friction in the bearings on the plane wheels - if there's no friction the plane will not be slowed. The amount of energy that would have to be dissipated through the wheels by them spinning and converting the kinetic energy from the thrust into thermo dynamic energy through friction is immense - it's the amount of energy produced by the engines. The wheels will melt or catch fire very quickly.

In any case, if the plane doesn't move there can be no lift from air travelling over the wings so the plane can't take off.
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Wow! .. A very scientific answer (y) that is completely wrong in its conclusion :D ... The plane will definitely be able to take off :)
 
Splog said:
Wow! .. A very scientific answer (y) that is completely wrong in its conclusion :D ... The plane will definitely be able to take off :)
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I/you must be missing something here.

The plane is not moving (equate to runner on treadmill). There is no airflow (equate to runner on treadmill). Ergo no lift, ergo no fly. Simples!

Unless, as someone said earlier, it's a VTOL.
 
davek said:
I/you must be missing something here.

The plane is not moving (equate to runner on treadmill). There is no airflow (equate to runner on treadmill). Ergo no lift, ergo no fly. Simples!

Unless, as someone said earlier, it's a VTOL.
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It's not VTOL!

Why won't the plane move? The plane will move and it will take off :)
 
The plane will take off as normal so long as the wheels can withstand travelling at twice the rpm as usual during the takeoff run. Nothing else changes.
 
Nothing is driving the wheels - they only freewheel. The engines / jets / prop work against the air around them dragging the plane forward whatever happens. The wheels will just turn at twice the normal speed if the treadmill is going the oposite way at the same speed. As the engines work against the air and thrust the plane forward, it WILL take off as normal.

The only way the plane would not take off is if ONLY the wheels were driven by the engines (no jets or prop) but then you would have a glider in effect
 
theMusicMan said:
Consider this folks, and is why I remain non decided.

Place a car on a treadmill, brakes off, in neutral, turn the treadmill on... what would happen...?

Turn the treadmill on slowly and the car would probably move with the treadmill. Turn the treadmill on quickly thus overcoming the inertia of the car, and possibly the car would stay still in space, but the wheels would turn (assuming minimal friction etc)

With me so far...?

Crank the speed of the treadmill up and the car remains physically stationary, but the wheels turn at the same speed... come to a constant speed and we have the car not moving in space with the treadmill running, and the wheels turning.

Agreed...?
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It will

the problem is cars are driven by the wheels, if the plane was it woulnd't be able to take off (or move) BUT the engines push it along relative to the air, the conveyor belt will add load but the plane will still take off (if it has the power to counter the load)
 
david1701 said:
It will

the problem is cars are driven by the wheels, if the plane was it woulnd't be able to take off (or move) BUT the engines push it along relative to the air, the conveyor belt will add load but the plane will still take off (if it has the power to counter the load)
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Good answer :) but what is the load from the conveyor belt? .. :thinking:
 
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