AQ500 & BMatthews,

It's a little harsh and misleading to refer to flaps as a band-aid for high speed airfoils. Actually, they are a clever way to allow a small, efficient wing to generate more lift than is needed in cruise. They definitely apply here, as the CL will be far from constant. While we naturally associate flaps with take-off and landing, they are more generally applied than that. In fact, flaps are indeed used successfully on some model sailplanes and pylon planes, specifically to give higher CL when needed, and not just for take-off and landing. The case of a pylon plane, which needs very low CL most of the time and moderate CL for turns, is fairly similar to the duration problem we are discussing.

I think I would characterize this decision as a tradeoff between imperfectly implemented variable camber and well implemented ( smooth, lower drag ) constant camber. One is an attempt to tune camber for the varying weight, and pays a small drag penalty, while the other is an attempt to choose a camber which is OK for the whole flight, and also pays a drag penalty for having too much camber late in the flight, when CL is lower. I can't prove which is better, but the fact that some sailplanes & pylon planes are managing the implementation problems suggests to me that a careful implementation of "camber flaps" would give superior performance.

It might even be feasible to arrange the fuel tanks to counter the pitching moment caused by the flaps, by having the first fuel tanks to empty be behind the CG. Ideally, we could avoid huge elevator inputs to deal with the changing pitching moment of the wing.

banktoturn