> Russell, take a look at blade calculations for impulse 
> turbines. A flat plate
> has no lift as such (the paths are equally long around 
> both sides), it works as
> a deflector mostly. And its efficiency is low.

Surprisingly, and not overly intuitively until you've 
wandered through the various descriptive pages a few times, 
a flat plate does provide lift - as Sean says, for a flat 
plate,  maximum lift occurs at 45 degrees (!). It also has 
substantial drag. Some specialist aircraft have wings 
approaching flat plates. One example is very fast aircraft - 
especially it seems older fast ones. Starfighter comes to 
mind without going and looking how flat they are.

Lift occurs when you deflect an airstream such that there is 
an "easy" and "hard" path (or lower and higher resistance, 
or preferred and non preferred or ...). How you view what 
happens after that depends on which method of analysis you 
choose. There are various nice effects to complicate things. 
(Messrs Coanda, Bernoulli, Reynolds and more stand in the, 
er, wings)


        Russell


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