Originally Posted by LD Max
So I must accept that you are right to say that positive pressures often exist below a cambered aerofoil. However, they never do appear to dominate and negative pressures certainly DO exist while lift is being generated at "normal" AoAs.
I think I'd concede that. Well argued!
Foilsim's fun, isn't it?!
I would imagine that a typical "design" cruise Cl is of the order of 0.3 to 0.4 for a light aircraft (perhaps less for transport aircraft). With your symmetric aerofoil, I'd agree that the average Cp is negative. But for the flat plate it's most definitely positive.