For some years now an increasing amount of experimental and theoretical work has been done to obtain a deeper understanding of separated vortex flow associated with slender wings. Most of it has been concerned with flat plates or thin wings.

Slender thin wings with leading-edge separation have high lift-dependent or vortex drags, and lift-dependent drag factors are usually well above unity. Thick symmetrical wings also have high values of lift-dependent drag factor. On a slender wing with leading edge separation, no leading edge thrust is obtained but by suitable! addition of thickness, the high suction peak underneath the main vortex can be made to act on a forward facing surface to give a reduction in drag.