Reflexing ailerons like on gliders and the Flight Design CT reduces drag because the aerofoil is designed to run laminar flow far back on the lower surface with the flap in the reflexed position. When the flap is down the pressure gradient ahead of the flap causes transition of the laminar b.l. earlier. On modern gliders with cruise (reflexed) flaps, the curvature is continuous over the flap hinge, the hinge line itself if faired over with flexible mylar and the laminar b.l. runs all the way onto the flapperon with forced transition via blowholes (pneumatic turbulators) at 95% chord. With careful design elements like this it is possible to acheive a max L/D of 52 on an 18m glider!
OG