winglets

A small, nearly vertical, winglike surface usually shaped like the airfoil section attached to the wing tip. The surface may or may not have control surfaces. It is generally located rearward above the wing tip and is effective in reducing the induced drag by reducing the spilling of high-pressure air beneath the wing to a lower pressure above the wing. Two small vortices create less drag than one huge vortex; thus, they create less of a hazard to aircraft following on approach through a less-induced wake turbulence. Winglets are most effective at a low speed or high alpha, where the induced drag is the highest. They may produce a forward component of lift as well as reduce the induced (vortex) drag, thus improving the range of long-range as well as short-range commuter jets. Also called wing-tip winglets, blended-wing tips, blended winglets, tip sails, or wing-tip sails. See also wing-tip sail.