Originally Posted by JetPlaneFlyer
Actually anything that 'prevents' separation improves (as in helps delay) stall. Stall is by definition what happens when you have flow separation on the top surface of the wing, so anything that promotes separation also promotes stall.
while its true that stall (or at least huge drag) occurs on full separation its also true that separation on 50% or so of the upper surface is maximum lift.
imo the big advantage of kf is not so much that it delays stall (which can be very sudden and violent on laminar flow wings) but rather causes a more gradual onset and easier recovery. the ultralight guys refer to it as "mushing". i think separation occurs with kf at very low speeds which does improve lift and makes the plane feel so much more "friendly".