Fabric-covered Clark Y Max Coefficient of Lift I'm looking at the Aeronca C-3 Collegian, which had a Clark Y airfoil, and I'm finding the following:


Wing area: 142 ft²
Empty weight: 466 lbs
Payload: 470 lbs
Stall speed: 38 mph


When I do the math for that wing area, a gross weight of 936 lbs, and a stall speed of 38 mph, I get a coefficient of lift of of about 1.8; that's higher than I see from either simulations or wind tunnel tests.

I'm inclined to trust these figures, since they line up with pilot reports on the C-3, and the airspeed range would be very narrow if the stall speed were higher; could it be that distortion of the fabric results in a later stall?  The little I could find on the subject doesn't suggest any such effect.  What's going on here?
One contributor with a lightweight airplane like the C-3 is thrust.  At a high angle of attack, a significant fraction of the engine's thrust is directed downward, lightening the loading that the wing's lift is working against.  Even at idle, this allows slowing further before the angle of attack becomes critical -- making the coefficient of lift appear higher than it is.