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Old 29 November 2007, 12:05   #71
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Originally Posted by visualpecepts View Post
If with no conveyor the plane was moving forward at 100mph, you then put a conveyor under it moving backward at 100mph, the plane would come to halt relative to the ground.
Only if the thrust was coming from the plane's wheels. It's not. The thrust is directed into the air, and it's that effect that creates the forward motion. The planes motion is created by the difference between the still air and the jet exhaust. Putting a treadmill at the same 100mph underneath just gets the wheels doing 200mph, with the plane still going forwards. To get the plane sitting still, you have to remove the recipient of thrust, i.e. the air; it has to be moving rearward at the 100 mph to get the plane to stand still. At that point, you've got airflow over the wings, which generates lift, and, well... see ya.

jky
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Old 04 February 2008, 21:16   #72
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Finally! The definitive answer!

[YOUTUBE]0ul_5DtMLhc[/YOUTUBE]

Told ya so....
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Old 05 February 2008, 02:01   #73
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That proved nothing. The plane was moving relative to the ground all the time. He was overcoming the slight backward motion of the belt by gunning the engine a bit harder to get ground speed = air speed = lift = flight.

It would have been more scientific if they had measured the air speed at takeoff with and without the belt.

One thing that has not been mentioned as far as I can see is the boundary layer effect (all fluids tend to stick to surfaces). The belt would tend to drag air along with it and provide lift to a plane maintaining its velocity over the belt in the opposite direction (whether still relative to the ground or not). The effect would probably be insignificant for the plane in the clip but it might be non-negligible on a small scale. The effect would quickly diminish as the plane lifted away from the belt but it is possible that flight might be maintainable just above it.

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Old 05 February 2008, 04:55   #74
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Old 05 February 2008, 19:18   #75
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Way over complicated
Pulling that "conveyor belt" leads to all discrepencies in co-efficent of friction between the wheels and the canvas and the ground beneath.
You would need a frictionless system (impossible) and computerised matching of belt and plane belt speed to get true effect.
Boils down to this.

Plane needs increased airflow over wings to provide lift.
So get on your 5 speed on a roller bearing.
Pedal slow and then pedal fast.
Do you feel the wind in your face
Nuff said
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Old 05 February 2008, 19:30   #76
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Originally Posted by limeydal View Post
Way over complicated
Pulling that "conveyor belt" leads to all discrepencies in co-efficent of friction between the wheels and the canvas and the ground beneath.
You would need a frictionless system (impossible) and computerised matching of belt and plane belt speed to get true effect.
Boils down to this.

Plane needs increased airflow over wings to provide lift.
So get on your 5 speed on a roller bearing.
Pedal slow and then pedal fast.
Do you feel the wind in your face
Nuff said
It's NOT THE WHEELS THAT ARE POWERED ON A PLANE AND THATS WHY IT TAKES OFF!!!!!!!!!
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Old 05 February 2008, 20:38   #77
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It's NOT THE WHEELS THAT ARE POWERED ON A PLANE AND THATS WHY IT TAKES OFF!!!!!!!!!
I don't think your going to convince them.
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Old 05 February 2008, 21:08   #78
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I don't think your going to convince them.
I tend to agree. Maybe I'll have more luck at this:-

Although you can see it's green,this grass is actually red.
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Old 05 February 2008, 23:33   #79
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The propellor provides the "pull" to increase the wings speed relative to the air
around it. No forward movement " relative to the air " ,so no decrease in pressure above the wing ,so no increase in lift on the areofoil , hence no flight.
Think someones pulling our plonkers
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Old 06 February 2008, 07:35   #80
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I have had RC planes in the past that will takeoff from a complete standing start just using thrust from the prop - will also take off vertically like a helicopter - it's all about power to weight ratio.
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