Who's right?
- Thread starter gurusan
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Athanor said:It won't take off as it won't make any forward motion to generate lift from air moving over the wings via a longer route than under. The key is this:
Clearly to generate lift the plane must move forward. To move forward it's wheels must rotate on the ground propelled forward by the force of the engines (in order to make progress down the runway forcing the stationairy air over & under it's wings). In this case the treadmill is moving in a equal and opposite direction to the force being applied by the engines (i.e. if the engines should in theory be propelling the plane down the runway at 120knots to take off, the treadmill running at 120knots in the opposite direction means in effect the plane is not moving and so there is no lift).
I'm off to bed now - my work here is complete
You are wrong. Airspeed is the speed of the aircraft relative to the air mass, not the ground. Groundspeed is the speed relative to the ground, not the airmass. Your understanding is seriously flawed. You couldn't be more wrong.
In the example you give, the aircraft is moving at 120Kts through the air mass. Anything below the wings is irrelevant, it has enough airspeed to fly. Switch the example around to landing. By your understanding if an aircraft were to touchdown at 120Kts on this conveyor runway, the aircraft would stop dead. That is not the case.
You are wrong.
Yes but the treadmill is on the ground. Groundspeed is irrelevant. The engines propel the aircraft against the air mass. They don't transfer drive through the wheels. If an aircraft is pointing into a 120Kt headwind but is stationary on the ground, it can still fly. It may not be moving relative to the ground but relative to the air mass, it is moving at 120Kts.Athanor said:
I know that - that's what i said...Scuzi said:
the plane never gets any purchase to move forward and gain airspeed. The treadmill adjusts to roll back at the same speed the plane is trying to move forward so instead of the plane rolling down a runway pushing itself through the air mass to generate lift all it's doing is keeping up with a treadmill.
You are wrong i'm afraid
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Scuzi is not wrong I'm afraid you areAthanor said:
I dunno - the inaginary motors that power the treadmill - it's he's treadmill not mineclv101 said:
The point is he clearly says the treadmill adjusts it speed backwards to match any forward motion of the plane so therefore the plane never moves forward.
It does move forward relative to the airmass. This is where your understanding is flawed.Athanor said:I dunno - the inaginary motors that power the treadmill - it's he's treadmill not mine
The point is he clearly says the treadmill adjusts it speed backwards to match any forward motion of the plane so therefore the plane never moves forward.
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Scam said:
Thats a good explanation
I'm gonna toss my two pence into this cause im in a debate mood 
The question asked is if the conveyor is moving in the opposite direction at the same speed the plane should be travelling forward. (i.e. if the tyres are spinning at a rate to move the plane at 100MPH, the conveyor would be moving at 100MPH the other way) Oviously, to achieve this effect in the real world the conveyor would have to be motorised or designed like a rolling road like you see in a car garage etc... both would have exactly the same effect.
While the plane is on the ground, all the engine thrust is used to overcome the friction between the planes tires and the ground. Sufficient force will propel the plane forward. The forward motion on the plane forces air over the wings to generate lift. When the plane is travelling at sufficient speed the lift is strong enough to allow the plane to become airborn.
However, if the conveyor is moving in the opposite direction at the same as the aircrafts tyres. All that thrust the engines provide is transferred through the freewheeling tyres into the conveyor belt instead of the moving the plane forward. Because of this no lift is generated on the wings, therefore, the plane is completely incapable of taking off. The only way the plane could take off in these circumstances would be if the wind was blowing fast enough over the wings to generate the sufficient lift. But if a plane requires a speed of (for example) 200MPH in zero wind conditions, the head wind would have to be going 200MPH to cause the plane to lift off from a stationary position.
Think of it like a Formula 1 car sat on a rolling road. You can rev the engine all you like, all that will happen is you make the rollers spin faster all those aerodynamics will be useless because no air will be flowing over them. But a rolling road is rollers that are freewheeling. The conveyer for the plane would have to be motorised and controlled to allow it to travel in the opposite direction at the same speed the tyres are going.
Hell, replace the conveyor with a rolling road like in car garages and you've got exactly the same effect. All that thrust is transferred into the conveyor/rolling road through the tyres. The tyres are spinning which is the aim of the thrust but the ground is moving where as normally it isn't.
So simply put. If the ground (conveyor) is moving in the opposite direction at the same speed to keep the plane stationary, then NO, it will never take off.
Enjoy
The question asked is if the conveyor is moving in the opposite direction at the same speed the plane should be travelling forward. (i.e. if the tyres are spinning at a rate to move the plane at 100MPH, the conveyor would be moving at 100MPH the other way) Oviously, to achieve this effect in the real world the conveyor would have to be motorised or designed like a rolling road like you see in a car garage etc... both would have exactly the same effect.
While the plane is on the ground, all the engine thrust is used to overcome the friction between the planes tires and the ground. Sufficient force will propel the plane forward. The forward motion on the plane forces air over the wings to generate lift. When the plane is travelling at sufficient speed the lift is strong enough to allow the plane to become airborn.
However, if the conveyor is moving in the opposite direction at the same as the aircrafts tyres. All that thrust the engines provide is transferred through the freewheeling tyres into the conveyor belt instead of the moving the plane forward. Because of this no lift is generated on the wings, therefore, the plane is completely incapable of taking off. The only way the plane could take off in these circumstances would be if the wind was blowing fast enough over the wings to generate the sufficient lift. But if a plane requires a speed of (for example) 200MPH in zero wind conditions, the head wind would have to be going 200MPH to cause the plane to lift off from a stationary position.
Think of it like a Formula 1 car sat on a rolling road. You can rev the engine all you like, all that will happen is you make the rollers spin faster all those aerodynamics will be useless because no air will be flowing over them. But a rolling road is rollers that are freewheeling. The conveyer for the plane would have to be motorised and controlled to allow it to travel in the opposite direction at the same speed the tyres are going.
Hell, replace the conveyor with a rolling road like in car garages and you've got exactly the same effect. All that thrust is transferred into the conveyor/rolling road through the tyres. The tyres are spinning which is the aim of the thrust but the ground is moving where as normally it isn't.
So simply put. If the ground (conveyor) is moving in the opposite direction at the same speed to keep the plane stationary, then NO, it will never take off.
Enjoy
But how would any "force" from the treadmill get to the plane's body to counter the engines as there's no friction between the treadmill and wheels?Athanor said:I dunno - the inaginary motors that power the treadmill - it's he's treadmill not mine
Although you're not reading the question.Scuzi said:
The engines run.
The plane rolls forward (passing through the air to generate lift).
In this case however instead of rolling forward the treadmill matches the forward motion with a reverse motion of the same speed so the wheels never make any forward progress as the ground is in effect slipping out for under it.
it's nothing to do with being a pilot, it's basic physics