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Looking through the NACA archives turns up some really interesting stuff! A technical note from May of 1940 compairs a Gwinn flap with a plain flap. Note that a Gwinn flap is essentially a flat plate attached to the aft end of the airfoil. Just about like many of our stunters today.

Some observations:
at 0 deg flap deflection the airfoil with the Gwinn flap (this would be like a Flight Streak airfoil) produced a higher max Cl than the plain flap at 0 Deg deflection. Cl max of 1.19 for the Gwinn and 1.09 for the plain flap. The plain flap would be the same as an unflapped airfoil. The Plain Flap produced a higher rate of CL change with flap deflection but the Gwinn produced a higher Cl max. Meaning that you need more Gwinn flap deflection (and get more drag) to achieve a specific Cl but the Gwinn can achieve a higher Cl max.

It sounds to me like Al Rabe independently duplicated much of these findings in his evaluation of flap shapes...

Thanks, Ron!

We had discussed this a bit previously, but there was disagreement. It seemed to me that the flat stationary flap might be better at t.e. flow management at angles of attack greater than zero, since it deflected the higher pressure flow under the wing more sharply downward. Anyway, I just yesterday e-mailed two SSW friends about whether I should stick to my original plans for including one on my high-A/R flapless project or take the easier approach of just continuing the t.e. sheeting taper to a sharp edge. Now, I'll get back to the NACA site and pull up that TN! I hope they have some data on final t.e. shape.

SK