 Quote by tsimon
Why does flow separation give less lift?
A separated "suction side" would in my pov give zero pressure (which is the lowest possible).
And low pressure on suction side is, of course, beneficial.
I think I got it now; as the pressure can not drop further a increase in angle of attack will produce less lift as the projected force (integration of pressure difference) in "lift direction" will be smaller.
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First, you can't have "zero pressure" unless you are in a vacuum.
Anyway, when the flow separates, you get a separation bubble which is a local area of the flow where the boundary layer has detached and formed a circulating bubble between it and the surface. In this bubble, velocities are typically much lower than underneath. When you slow a fluid down, the static pressure rises, so now you have a higher pressure above the airfoil than below in certain points. That can lead to a loss of lift, and in some situations, even the opposite effect.