Tatoo,

Just found this thread. Most inserting discussions on airfoils, stab placement etc. Many thanks for this, learned a lot.

I'd bet that if you built a true, flat bottom wing with detachable leading edges and experimented, you'd find that sharp leading edges work best within a narrow speed range and angle of attack. You see a lot of them on free flights. Contrast this with some of the full size, extreme aerobatic, planes. They take the blunt leading edge concept to the extreme and it works well, for the pupose intended.

The airfoil on the Big Ugly, apparently contains an element not present on other airfoils that compensates for the well established notion that sharp leading edges are, generally, detrimental. That difference is the long, thin, trailing edge downward reflex. A negative angle of attack, renders this portion of the wing ineffective. At positive angles of attack, this reflex "grabs" a lot of air and compensates for any excess up-pitch. It's like having automatic down elevator every time the wing pitches up due to the sharp leading edge. It's this downwash part of the wing that prevents the oscillations around neutral.

Kudos on the innovative hollow airfoil. That it works well is most intriguing. How about anyone with access to a wind tunnel doing some tests and getting back to us?