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Post by Chris on Feb 2, 2006 5:16:08 GMT -5
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).
Does the plane ever take off, and why or why not?
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Post by JayP on Feb 2, 2006 5:24:57 GMT -5
No SOG = no lift = plane going no where unless it's a VTOL!
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Post by Clydesider on Feb 2, 2006 5:25:46 GMT -5
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction). Does the plane ever take off, and why or why not? No. Because the plane is effectively stationary. The plane requires air to flow over its wings at a sufficient speed to create a pressure deficit on the upside of the wings. The means that the greater pressure on the underside of the wings pushes the wings, and hence the plane, upwards. If no air flows over the wings, no lift is created.
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Post by Clydesider on Feb 2, 2006 5:26:29 GMT -5
Good point. Never thought of that.
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Post by "Squatter" on Feb 2, 2006 5:29:57 GMT -5
Chris,
Of course the plane will take off, once the flying speed is reached, and suficient airflow is achieved over the wing, low pressure will move from the top of the wing to the high presure below the wing (airfoil) and this will create lift, the pilot will gently pull back on the controls, activating the elevator and the plane will be airborne.
Simmilar system was used to launch a microlight off the roof of a car.
Another example - Inflate a paraglider on the side of a hill - (with a strong enough breeze) Stand dead still and apply break preasuer - wala - you are airborne...........
Perhaps this could be a new plan for launch control at Heathrow, hate to land on one though................
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Post by The Handsome Stick on Feb 2, 2006 5:44:10 GMT -5
Chris, Of course the plane will take off, once the flying speed is reached, and suficient airflow is achieved over the wing, low pressure will move from the top of the wing to the high presure below the wing (airfoil) and this will create lift, the pilot will gently pull back on the controls, activating the elevator and the plane will be airborne. Simmilar system was used to launch a microlight off the roof of a car. Another example - Inflate a paraglider on the side of a hill - (with a strong enough breeze) Stand dead still and apply break preasuer - wala - you are airborne........... Perhaps this could be a new plan for launch control at Heathrow, hate to land on one though................ But if the conveyor is moving in the opposite direction and at equal speed to the acceleration of the plane, it is stationary. There is no airflow.
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Post by T.P. on Feb 2, 2006 5:47:53 GMT -5
I'm going to say no it doesn't. It's the difference between running on a road and being on a treadmill. When you run on a road, you feel air flow past your face. In a similar way a plane needs this airspeed to take off. When you're on a treadmill you don't have this air flowing past your face, no airspeed, no take off.
T.P.
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Post by "Squatter" on Feb 2, 2006 5:50:28 GMT -5
Ok...............
I suppose you can say there will be no airflow theorectically.........................
Guess its like wheel spinning a car, wheels are turning, no grip, no movement....................
A wing will only fly if there is airflow................
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Post by Sewinbasher on Feb 2, 2006 5:52:01 GMT -5
I'd have to agree with TP and the others that say no. The plane needs airflow over the wing to create lift and this would not happen in this scenario.
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Post by tigermoth on Feb 2, 2006 6:03:30 GMT -5
Now then - think about when you run on a treadmill in a gym (god forbid) - as you increase your running speed, you can increase the speed of the treadmill. Do you feel the force of air/wind in your face..............?
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Post by ChrisNicholls on Feb 2, 2006 6:11:18 GMT -5
OH no not again!
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Post by MichaelL on Feb 2, 2006 6:32:04 GMT -5
Ok............... I suppose you can say there will be no airflow theorectically......................... Guess its like wheel spinning a car, wheels are turning, no grip, no movement.................... A wing will only fly if there is airflow................ You were right the first time. The aircraft will still take off (its not a car).
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Post by clockwork on Feb 2, 2006 6:33:43 GMT -5
I think the question here is not will it fly, but will it move?
I dont think the plane needs the wheels to run on the treadmill in order to move, the Engine Blowing Air (or Props) will thrust it forward, it doesn't need the conveyor.
The wheels will spin really fast though. It looks at first like the plane will stand still, but when you look at it as a plane, and not as a car which drives the wheels, you will see the potential for flight.
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Post by T.P. on Feb 2, 2006 6:39:04 GMT -5
Now then - think about when you run on a treadmill in a gym (god forbid) - as you increase your running speed, you can increase the speed of the treadmill. Do you feel the force of air/wind in your face..............? No you don't feel the wind increase. There are 2 speeds in flying, ground speed and airspeed. Your ground speed can be zero (you're basically going nowhere) but you won't drop out of the sky if you have sufficient airspeed. How does this work? Well if you're moving forward via jet propulsion and the head wind is the same as your forward thrust then you're going nowhere but there is lots of air flowing over the wings, creating lift. Sounds really similar to the treadmill, but it isn't. On the treadmill you're running forward - think of that as the thrust of the plane engine. If you ran along a road your airspeed would increase (you hear the air flow past your ears). When you're standing still and running (EDIT, that was very Irish as my Mother would say, I mean running on the spot), no airflow past your ears. No airflow, no lift. This plane could theoretically take off if the flaps were in the right position and wind was blown at a strong enough strength to create enough airflow to create lift. This is how a kite works when you first let go of it. Planes need a lot of airspeed to take off, hence the huge acceleration and they take off into the wind. When thinking about planes flying, think about kites or in my case hang gliders, they display exactly the smae principles as planes but in much simpler ways. If you ran on the spot with a kite in your hand and let go, what would it do? I don't think I've explained this very well. I hope this is a question with some jokey answer and we're all wrong! T.P.
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Post by Cothi on Feb 2, 2006 6:41:11 GMT -5
I am told there are about 5 pages of this boring rubbish on "The Beige Side" - as Chris fully knows.
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