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Old 5th September 2003 | 20:08
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CBLong
 
Joined: Jan 2002
Posts: 156
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From: Sandwich, Kent, UK
Hi Ryan,

The exact mechanism for the production of lift is quite controversial, but as you say, most authorities seem to agree that relying solely on Bernouilli is wrong. This site will give you a lot of background - try the link in the fourth bullet point labelled "critique".

For what it's worth (and I'm just a moderately maths / physics literate computer programmer / PPL), I think that whenever you get this sort of "holy war" over an issue, the most likely situation is that all the different points of view have some merit.

It's certainly true that the only way that any aircraft can generate any forces on itself (including lift, but also drag, thrust etc) is by applying a force on the surrounding air - it then feels the equal and opposite force as per Newton. Of course, applying a force to the air causes the air to accelerate, which leads to pressure diferentials, which lead to more accelerations, and so on - making it very difficult to analyse. Bernouilli's Theorem relates changes in velocity of a fluid to changes in its pressure, but it can't (easily) predict how much "change in velocity" will result from a given aerofoil moving at a given airspeed at a given angle of attack, etc.

I'm fairly sure that the Coanda Effect (the "water flowing round a spoon" thing) isn't relevant to aerofoils - the two situations are quite different... or so I've read...

Hope this helps... now that I've stuck my head above the parapet, let's see if my post starts a mini-"holy war" here!

Cheers,

cbl.
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