well known on propellers (centrifugal force causing an outward displacement of the boundary layer), or wings (boundary-layer suction). The leading-edge cuff inboard vortex and wing tip vortex act both to remove the boundary layer of the wing's outer section, helping this low-aspect-ratio virtual wing to achieve a higher stall angle. An important point is that the wing seems to be aerodynamically split in two parts, the inner stalled part and the outer part that behaves as an isolated low-aspect-ratio wing, able to reach a high angle of attack. The sharp discontinuity of the cuff is a key factor; all attempts by gradual fairing to suppress the vortex and the positive effects of the modification reintroduced an abrupt tip stall. Stall/spin results According to a NASA stall/spin report, "The basic airplanes: AA-1 (Yankee), C-23 (Sundowner), PA-28 (Arrow), C-172 (Skyhawk) entered spins in 59 to 98 percent of the intentional spin-entry attempts, whereas the modified aircraft entered spins in only 5 percent of the attempts and required prolonged, aggravated control inputs or out-of-limit loadings to promote spin entry." Wing aspect ratio and location effects The most successful NASA experimental results were obtained on a quite low 6:1 aspect ratio wing (Grumman Yankee AA-1), with a DLE placed at 57% of the semi-span. As the vortices (inboard cuff and wing tip) are efficient on a limited span length (about 1.5 times the local chord), a DLE alone is unable to preserve enough outboard lift to keep the roll control in case of high aspect ratio wing. Wings of more than 8 or 9 aspect ratio features other devices to complete the cuff effect, for example stall strips (as used on the Cirrus SR22 and Cessna 400), "Rao slots" (as used on the Questair Venture), vortex generators or segmented droop (as used on a NASA modified Cessna 210). In the case of the high aspect ratio Cessna 210 wing (AR =11:1), roll damping at stall was not as efficient. The case of high-wing configuration wing was different. Full scale testing of a modified Cessna 172 showed that the outboard leading-edge cuff alone was not sufficient to prevent a spin departure, the aircraft lacking directional stability at high angles of attack. With a ventral fin added, the aircraft entered a controlled spiral in lieu of a spin. Drag penalty Depending on the cuff length and shape, the leading-edge cuff can exert an aerodynamic penalty for