Who's right?

["andy"]

The engines draw in air and push it out the back. This causes the plane to move forwards, hence air flows over the wings and we get lift.

oooops lol i see what ive done wrong now , having had a few drinks i failed to apprehend that they suck air into the front

was trying to work it out as though they where just mad thrusters pushing "summit" out the back

oops , so yea it will definetly take off

 

[Jotun]

Then it would not remain on the treadmill. Or is this treadmill runway length..

I've been assuming so. If it is very short the plane will go off the treadmill and keep going until it took off (or hit something)

 

[jhmaeng]

Then it would not remain on the treadmill. Or is this treadmill runway length..

If the treadmill was only 200m long, even better - once the plane's off the treadmill, it can take off as normal against terra firma.

 

[VIRII]

Thing is, the plane is not stationary.

So how long is the treadmill, infact if the treadmill is not having the effect of keeping the plane in the same place why is it there?

 

[clv101]

As the plane is stationary and no air flows over the wings where does the lift come from?

It's not stationary though, it's moving forward due to the thrust of the engines.

 

[Shock]

So how long is the treadmill, infact if the treadmill is not having the effect of keeping the plane in the same place why is it there?

To confuse people.

 

[divine`]

So how long is the treadmill, infact if the treadmill is not having the effect of keeping the plane in the same place why is it there?

The treadmill matches the wheel speed. Planes wheels can spin freely (unless you put brakes on obviously)

It makes no difference how long the treadmill is, other than whether the plane fell off the end before it took off.

The treadmill is there purely for the purpose of starting this stupid argument.

 

[VIRII]

If the treadmill was only 200m long, even better - once the plane's off the treadmill, it can take off as normal against terra firma.

None of that makes any sense.
The engines provide thrust which pushes the plane forward which creates the lift, ie the movement of the wings through the air at speed.
If the item is on a treadmill and the wings are not moving forwards at 120mph or more then there is not enough lift for takeoff.

The siggestion so far seems to be that a jet engine arttached to a wing will take off VTOL style simply by the amount of air it sucks into the engine being pushed out the back.
That air is going into the engine, not over the wing.

 

[clv101]

The treadmill is there purely for the purpose of starting this stupid argument.

Amen to that! Goodnight all.

 

[Scuzi]

As the plane is stationary and no air flows over the wings where does the lift come from?

The aircraft isn't stationary as it has applied full power and accelerated through the air mass.

Think of it like this. A plane on skis and the conveyor/treadmill is covered in snow. The same principle applies. Even taking into account the negligible friction, the aircraft engines apply their force against the air mass. The equal and opposite reaction (as per Newtons law) is for the aircraft to accelerate in the opposite direction to the force. Since the force is being applied against the air and not against the conveyor surface, the aircraft will still accelerate relative to the air mass. It is Newtons law.

There is no force between the aircraft and the conveyor in the horizontal plane, hence why the conveyor cannot apply an opposing force in order to counter act the force from the engines. As long as the wheels are able to rotate freely, a force cannot be applied to the aircraft by the conveyor.

Physics at its most basic level. They teach this stuff to 10 year old kids FFS.

 

[VIRII]

The treadmill matches the wheel speed. Planes wheels can spin freely (unless you put brakes on obviously)

It makes no difference how long the treadmill is, other than whether the plane fell off the end before it took off.

The treadmill is there purely for the purpose of starting this stupid argument.

So the plane does not move forward then.
If it was 100m from my house even at full jet thrust it would (because of the treadmill) still be 100m from my house.
Then it won't take off. It'll just make a lot of noise.

 

[Blinkz]

hahahahahaha. I love this scenario, it confuses everyone

Scuzi and the select few that said it will takeoff are all correct. Aircraft engines provide thrust relative to the airmass not to the ground. The plane will accelerate and will take off.

 

[divine`]

None of that makes any sense.
The engines provide thrust which pushes the plane forward which creates the lift, ie the movement of the wings through the air at speed.
If the item is on a treadmill and the wings are not moving forwards at 120mph or more then there is not enough lift for takeoff.

The siggestion so far seems to be that a jet engine arttached to a wing will take off VTOL style simply by the amount of air it sucks into the engine being pushed out the back.
That air is going into the engine, not over the wing.

No, because it is a physical impossibility for the treadmill to cause any kind of opposing force to the thrust provided by the engines on the body of the plane. So the plane is moving. Moving plane = air over wings. Simple.

 

[jhmaeng]

Physics at its most basic level. They teach this stuff to 10 year old kids FFS.

There should be a sticky at the top of GD, titled "Thinking of asking whether a plane on a treadmill will take off?"

 

[VIRII]

There is no force between the aircraft and the conveyor in the horizontal plane, hence why the conveyor cannot apply an opposing force in order to counter act the force from the engines.

Physics at its most basic level. They teach this stuff to 10 year old kids FFS.

Quite, so the conveyor is utterly irrelevent and does NOT have the effect of keeping the plane in one place. Hence why I asked how long the conveyor was. However several people appear to be suggesting a plane can remain stationary and simply take off.

 

[VIRII]

No, because it is a physical impossibility for the treadmill to cause any kind of opposing force to the thrust provided by the engines on the body of the plane. So the plane is moving. Moving plane = air over wings. Simple.

Quite As i said earlier "is the treadmill runway length".

 

[Byron5184]

Ah screw it. I know the right answer. Thats good enough for me

 

["andy"]

you need to realise the enigne is sucking the plane forward into the air aswell as pushing air against air behind it ,

thats how it gets upto speed

if the wheels wherent wheels that spun freely then no it wouldnt take off


the early post about bearings melting is probably true tbh as the wheels will be spinning twice the speed they normally would be

 

[divine`]

Quite, so the conveyor is utterly irrelevent and does NOT have the effect of keeping the plane in one place.

Exactly. It is useles. It there purely for the purpose of confusing people.

Hence why I asked how long the conveyor was. However several people appear to be suggesting a plane can remain stationary and simply take off.

I don't think anyone suggested that. If they did they are wrong but I think most people are working on the (correct) assumption that the plane moves forwards.

Quite As i said earlier "is the treadmill runway length".

It can be 17 miles long if you want, the only difference it will make is that if it's shorter than a runway the plane will fall off the end before it's taken off, where as if it's longer it'll just move along it and take off normally.

 

[Scuzi]

Quite, so the conveyor is utterly irrelevent and does NOT have the effect of keeping the plane in one place. .

YES! EXACTLY!

The aircraft cannot remain stationary and take off (assuming nil wind conditions). People do not seem to realise this. The length of the conveyor is largely irrelevant, as irrelevant as the existence of the conveyor itself