colinusher

I am not sure if I agree with Dave's philosophy, although the results he achieved cannot be disputed. As he say's Lift = Drag but lift in level flight always = weight. (exactly) You cannot have too much lift or the model would go up like an elevator. The EXCESS lift is traded into speed, the modern sailplane gets from LIFT A to LIFT B (thro' sink) as fast as possible, burning off all that excess lift as speed. A model whose lift just about equals its weight will always stagger along on the verge of a stall. We have all seen flyers trying to stay up staggering along just on the stall, a bit of down elevator & the model shoots off & the lift piles in. With the Cof G in the correct place the model should fly with the tailplane at more or less zero incidence, flying with loads of UP or DOWN elevator will produce drag. The answer is to use an aerofoil that produces its lift over the estimated speed range & produces min drag. Unless you are using CNC milled wings to the exact design profile you are wasting your time anyway with ribs & a sagged covering. The QUANTUM leap in modern sailplane performance has come about due to the computer generated aerofoil design being transalated 100% into the actual wing & not a 50% near copy.