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Old Aug 02, 2006, 11:55 AM
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Something to think about.....Will it Fly? II

This is part II of the “Something to think about.....Will it Fly?” thread. The other thread was causing performance problems.

Orginal Question:

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?
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Old Aug 02, 2006, 12:01 PM
aka: A.Roger Wilfong
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AAAIIIEEEEE!!!!!!!!!!!!!!!!!!!!!!!!!

Not another &^(*$^%*$^%#&#!@#*&)!#@^@ one!

- Roger
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Old Aug 02, 2006, 12:02 PM
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Hugequark's Avatar
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There we go. Figured you'd start part II, thanks. And yeah Will, I couldn't avaoid the heat that long last night. Had to see what was going on. And I only have like a 10 min commute
================================================== ========
Originally Posted by Buzz
///Tilting it vertically has nothing to do with it. ///




It does 100%. If you say the plane can't move while the belt is horizontal, then it will also be true if you tilt the belt vertical. The angle shouldn't matter. Tilting it is just my way of getting you guys to visualize the force induced by thrust.
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Old Aug 02, 2006, 12:14 PM
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Originally Posted by Hugequark
There we go. Figured you'd start part II, thanks. And yeah Will, I couldn't avaoid the heat that long last night. Had to see what was going on. And I only have like a 10 min commute
================================================== ========
Originally Posted by Buzz
///Tilting it vertically has nothing to do with it. ///




It does 100%. If you say the plane can't move while the belt is horizontal, then it will also be true if you tilt the belt vertical. The angle shouldn't matter. Tilting it is just my way of getting you guys to visualize the force induced by thrust.
Don't think you’ll get much support on this one.

The more tilt you put in the less force of gravity has on the plane against the conveyor belt until it reaches 0 at vertical. This has nothing to do with the question.

Will
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Old Aug 02, 2006, 12:18 PM
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The only way the plane will lift off is if it creates lift. Left is created by moving through the air. When it is sitting on the conveyor belt, it is not moving through the air. No matter how fast the plane (and belt) move, it will still remain in the same position, and thus not move through the air.

I don't see what the big debate is about. The belt is preventing it from moving. It's effectively gluing the plane to the ground.
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Old Aug 02, 2006, 12:25 PM
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Quote:
Originally Posted by willhaney
Don't think you’ll get much support on this one.

The more tilt you put in the less force of gravity has on the plane against the conveyor belt until it reaches 0 at vertical. This has nothing to do with the question.

Will
Gravity is constant. How am I reducing gravity by tilting? Am I also reducing the plane's mass?

The tilting will find the breakaway point between the wheels and the belt. This breakaway point will also exist when the belt is horizontal. That is just a fact, you can't argue that one. Unless of course the belt is magic.
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Old Aug 02, 2006, 12:28 PM
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Quote:
Originally Posted by pilot89
The only way the plane will lift off is if it creates lift. Left is created by moving through the air. When it is sitting on the conveyor belt, it is not moving through the air. No matter how fast the plane (and belt) move, it will still remain in the same position, and thus not move through the air.

I don't see what the big debate is about. The belt is preventing it from moving. It's effectively gluing the plane to the ground.

The debate is because the belt doesn't stop the plane from moving in the air, just the wheels from rotating. If it were a car and the rotation of the wheels were the source of movement then it would stay still. But the movement is caused by the prop in the air, thus the wheels won't turn but the plane will still move and cause lift. If the plane where attached by the wheels so that they had to turn for the plane to move then it couldn't lift off.
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Old Aug 02, 2006, 12:38 PM
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Quote:
Originally Posted by Hugequark
Gravity is constant. How am I reducing gravity by tilting? Am I also reducing the plane's mass?

The tilting will find the breakaway point between the wheels and the belt. This breakaway point will also exist when the belt is horizontal. That is just a fact, you can't argue that one. Unless of course the belt is magic.
Did I say you are "reducing gravity by tilting"?

No. I didn't.

I said "less force of gravity has on the plane against the conveyor belt until it reaches 0 at vertical"

Does gravity have any effect on the plane in relation to the belt now?:
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Old Aug 02, 2006, 12:39 PM
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Quote:
Originally Posted by Hugequark
How am I reducing gravity by tilting?
By removing it's influence.

Will
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Old Aug 02, 2006, 12:43 PM
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Quote:
Originally Posted by willhaney
Did I say you are "reducing gravity by tilting"?

No. I didn't.

I said "less force of gravity has on the plane against the conveyor belt until it reaches 0 at vertical"

Does gravity have any effect on the plane in relation to the belt now?:
Yes. If the wheels are making contact, gravity has an effect.
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Old Aug 02, 2006, 12:59 PM
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Quote:
Originally Posted by Hugequark
Yes. If the wheels are making contact, gravity has an effect.
Really, how?

How is gravity pushing the plane against the belt when they are both vertical?

Will
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Old Aug 02, 2006, 01:08 PM
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Now will it move?
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Old Aug 02, 2006, 01:11 PM
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Will it take off?
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Old Aug 02, 2006, 01:19 PM
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Quote:
Originally Posted by willhaney
Really, how?

How is gravity pushing the plane against the belt when they are both vertical?

Will
Your diagram has the wheels making contact, does it not? Then there will be initial interaction until the wheels no longer are in contact. The problem is, breakaway will be achieved way before vertical. This means that the force needed for breakaway is less than the weight of the plane. And that breakaway value will be the same horizontally. The belt can speed up all it wants, but the real laws governing this type of interaction between matter, will not change. You can word it any way you want.

Now, had the question included a clause wherein we are supposed to suspend laws of physics, I would concede immediately and agree that the plane would be forever stuck in the same exact spot. But as it was originally worded, I need to know the weight of the plane, as well as the amount of thrust to answer correctly. So what I am doing is generalizing without these values. And the truth of the matter is that any plane, model or full scale, will need less than it's own weight in thrust to break away from the belt. One needs to understand that the belt can not exert more force than the weight of the plane. Not at 5mph, nor 1,000,000mph. And I say this because the question does NOT tell me to suspend the known laws of physics.
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Old Aug 02, 2006, 01:29 PM
I fly, therefore I am.
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No. Mainly 'casue I wanna follow this new thread. Why'd they change it again?!
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Last edited by Cessna 182; Dec 20, 2006 at 02:36 PM.
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