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Old 7th Aug 2006, 22:14
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LD Max
 
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Originally Posted by porridge
I have been intrigued for sometime that why aerofoils develop lift is due to a combination of Bernouli's principles along with Coanda effect. Read this interesting paper: http://www.aa.washington.edu/faculty/eberhardt/lift.htm
- "A Physical Description of Flight"

Thanks for this link. Unfortunately it doesn't start out well, because it accuses the Bernoulli theorems of depending upon equal transit times in order to explain the differing velocities. Actually, Bernoulli's theorem says nothing of the sort, but is often misquoted in this way in popular texts. This is, indeed, one good reason for this thread!

The Coanda Effect you refer to explains the phenomenon that air "Sticks" to the surface of the wing as it moves through the air mass. (Similar, I believe, to a ping-pong ball held against a stream of water).

It is said that this effect causes the air molecules to change direction, and contribute to the lift in some way. I suspect that it is merely this turning effect which plugs energy into the Bernoulli equations to generate pressure differentials and gradients. These pressures may, in turn, be determined by measuring their associated air velocities. Notice I shy away from saying that an increase in airspeed CAUSES a drop in pressure. Bernoulli does not actually say this. He merely says pressure and velocity are related. If solved correctly, Bernoulii predicts extremely accurate models and are used as the basis for modern Computational Fluid Dynamics.

With thanks to Unfazed above, who steered me to another thread, this link seems to put the Coanda Effect in its proper place.


:-)

Last edited by LD Max; 7th Aug 2006 at 22:46.
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