Why the plane takes off in laymans (my) terms
30 Oct '06 11:391 editSorry for the double (triple) thread but this needs to be explained properly and the other threads got off topic talking irrelevant stuff.
The easy part:
The plane will take off.
The hard part:
Thought experiment.
Imagine you are lying on your stomach on a large skateboard. Along-side you is a horizontal rail which you grab and use to pull yourself forward. Your hand pulling on the rail generates the force that pulls you forward. Nothing to do with the ground.
Now imagine you're still on your large skateboard on a big conveyor belt. The rail is not attached to the conveyor-belt and does not move. Can you see that there is no practical speed the conveyor belt could travel that could make you move backward? Your hand holding the rail can easily overcome the friction in the bearings pulling you back, you could easily pull yourself forward as if you were on a normal floor.
Now replace you + skateboard with a plane (I like to visualise a little Cessna) and replace your hand pulling on a railing with a propeller pulling the plane through the air. The propeller pulls air backward generating the force which moves the plane forward. Again, nothing to do with the ground.
You should agree now that no matter what speed the conveyor belt moves the plane will pull itself through the air, accelerate to its required velocity and take off.
The only difference between the take-off on a conveyor-belt runway and a conventional runway is that the little wheels under the plane would spin much faster on the conveyor-belt.
NOTE 1:
The answer is the same for a jet propelled plane except that a jet is pushing the plane forward instead of pulling it like a propeller.
NOTE 2:
To those sidetracked by the propeller pulling air over the wing generating lift - you are kidding yourself.
Disagree?
Lets do another thought experiment (location Fairyland).
Your plane is anchored to an immovable pole by a strong cable stretching from the tail of your plane to the pole. You spin up the propellers to top speed generating sooooo much air movement over your wings that you get enough lift to lift off. Momentarily you are hovering held down only by the cable, you click a button releasing the cable and quickly accelerate forward and fly away.
If this were possible runways would only be for landing on and the last time i flew in a propellered plane i vaguely remember rolling forward faster and faster until the massive amount of air moving over the wings (caused by forward motion) generated the lift to get us off the ground.
I concede that with 2 very large propellers spinning extremely fast, over a specially designed wing on an extremely light plane this scenario MAY be possible but i doubt it. I don't know enough aerodynamics to explain why but i really doubt it. If anyone has evidence to the contrary, please post. I'm skilled at own-word eating.
The easy part:
The plane will take off.
The hard part:
Thought experiment.
Imagine you are lying on your stomach on a large skateboard. Along-side you is a horizontal rail which you grab and use to pull yourself forward. Your hand pulling on the rail generates the force that pulls you forward. Nothing to do with the ground.
Now imagine you're still on your large skateboard on a big conveyor belt. The rail is not attached to the conveyor-belt and does not move. Can you see that there is no practical speed the conveyor belt could travel that could make you move backward? Your hand holding the rail can easily overcome the friction in the bearings pulling you back, you could easily pull yourself forward as if you were on a normal floor.
Now replace you + skateboard with a plane (I like to visualise a little Cessna) and replace your hand pulling on a railing with a propeller pulling the plane through the air. The propeller pulls air backward generating the force which moves the plane forward. Again, nothing to do with the ground.
You should agree now that no matter what speed the conveyor belt moves the plane will pull itself through the air, accelerate to its required velocity and take off.
The only difference between the take-off on a conveyor-belt runway and a conventional runway is that the little wheels under the plane would spin much faster on the conveyor-belt.
NOTE 1:
The answer is the same for a jet propelled plane except that a jet is pushing the plane forward instead of pulling it like a propeller.
NOTE 2:
To those sidetracked by the propeller pulling air over the wing generating lift - you are kidding yourself.
Disagree?
Lets do another thought experiment (location Fairyland).
Your plane is anchored to an immovable pole by a strong cable stretching from the tail of your plane to the pole. You spin up the propellers to top speed generating sooooo much air movement over your wings that you get enough lift to lift off. Momentarily you are hovering held down only by the cable, you click a button releasing the cable and quickly accelerate forward and fly away.
If this were possible runways would only be for landing on and the last time i flew in a propellered plane i vaguely remember rolling forward faster and faster until the massive amount of air moving over the wings (caused by forward motion) generated the lift to get us off the ground.
I concede that with 2 very large propellers spinning extremely fast, over a specially designed wing on an extremely light plane this scenario MAY be possible but i doubt it. I don't know enough aerodynamics to explain why but i really doubt it. If anyone has evidence to the contrary, please post. I'm skilled at own-word eating.
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