A leading-edge cuff is a fixed aerodynamic wing device employed on fixed-wing aircraft to improve the stall and spin characteristics. Cuffs may be either factory-designed or an after-market add-on modification. A leading-edge cuff is a wing leading-edge modification, usually a lightly drooped outboard leading-edge extension. In most cases of outboard leading-edge modification, the wing cuff starts about 50–70% half-span and spans the outer leading edge of the wing. The main goal is to produce a more gradual and gentler stall onset, without any spin departure tendency, particularly where the original wing has a sharp/asymmetric stall behaviour with a passive, non-moving, low-cost device that would have a minimal impact on performance. A further benefit is to lowering stall speed, with lower approach speeds and shorter landing distances. They may also, depending on cuff location, improve aileron control at low speed. Terminology Leading-edge cuffs were called droop concept or drooped leading edge (DLE), or modified outboard leading edge in technical reports on stall/spin resistance. In these reports and others NASA reports on the same object, "leading-edge cuff" expression was not used. Other authors use simply "cuff" or "wing cuff". History NASA led a general aviation stall/spin research program during the 1970s and 1980s, using model and full-scale experiments, seeking an effective means to improve stall/spin characteristics of general aviation airplanes. The effect of a central notch at mid-span on the wing maximum lift was demonstrated in 1976. Following the testing of different leading-edge modifications on models and full-sized aircraft NASA eventually selected the semi-span drooped leading edge (DLE) that was tested first on an American Aviation AA-1 Yankee (1978). A 1979 NASA report explains that at high angles of attack the cuff discontinuity generates a vortex that acts as a fence, preventing the separated flow from progressing outboard. The lift slope has a flatter top and the stall angle is delayed to a higher angle. To reach high angles of attack, the outboard airfoil has to be drooped, some experiments investigating "exaggerated" drooped leading edges. The physical reason for the cuff effect was not clearly explained. Some much older reports gave some similar results. A 1932 NACA report about the effect of leading-edge slots of various lengths said, "this is an indication that the slotted portion on each tip of the wing operates to some extent as a separate wing". Getting higher lift coefficients as a result of boundary layer removal is