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Old 22 November 2007, 11:54   #31
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But the wheels do not propel the plain it is the thrust from the engines, so it will take of as normal moving forward through the air creating lift under the wing!
But it will not be moving forward in relation to the surrouding air because the conveyor is running backwards at an equal velocity to the engines take off velocity. So, the plane appears to be stationary as far as air flow is concerned.
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Old 22 November 2007, 12:28   #32
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If the engines are off and the plane sits on a moving conveyor which direction does the plane go?

if there is "zero friction" in the tyres/bearings then they just spin and the plane remains stationary.

If friction is considered the plane moves at the same speed (and direction) as the conveyor (as it would with the brakes on) then why with the engines on providing forward thrust is there no longer a thrust in the opposite direction from the conveyor"?.

Anyone going to try it with a model at the local gym?
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Old 22 November 2007, 12:28   #33
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But it will not be moving forward in relation to the surrouding air because the conveyor is running backwards at an equal velocity to the engines take off velocity. So, the plane appears to be stationary as far as air flow is concerned.
Can you explain how the conveyor has an effect on the thrust of the engines? The engines do not propel the wheels, they push against the air, therefore the plane will go forwards in relation to the air and the surrounding ground, and at double the speed in relation to the conveyor.

The conveyor velocity does not equal the engines velocity as they are not connected!
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Old 22 November 2007, 12:50   #34
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The conveyor velocity does not equal the engines velocity as they are not connected!
Correct. The conveyor velocity is equal-and-opposite to the potential take-off velocity of the plain.

Therefore, the plane will effectively be stationary in its air space, Yes, the wheels will be going twice as fast but this is irrelevant.
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Old 22 November 2007, 13:02   #35
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Quote:
Originally Posted by Polwart View Post
If the engines are off and the plane sits on a moving conveyor which direction does the plane go?

if there is "zero friction" in the tyres/bearings then they just spin and the plane remains stationary.

If friction is considered the plane moves at the same speed (and direction) as the conveyor (as it would with the brakes on) then why with the engines on providing forward thrust is there no longer a thrust in the opposite direction from the conveyor"?.

Anyone going to try it with a model at the local gym?
As i said i have had a very simlar situation with my model planes.

James
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Old 22 November 2007, 13:05   #36
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http://www.straightdope.com/columns/060303.html

That explains it pretty much
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Old 22 November 2007, 13:13   #37
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Yep, that explanation is a good one. Sorted.
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Old 22 November 2007, 13:48   #38
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OK, what happens if a really fat guy carrying an 8 x 4 sheet of ply walks past the back of the plane?
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Old 22 November 2007, 13:51   #39
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OK, what happens if a really fat guy carrying an 8 x 4 sheet of ply walks past the back of the plane?
Imagine that the man is the second truck



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Old 22 November 2007, 14:22   #40
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