Wing tip flow control

In a fluid foil having a span with a root at one end and a tip at the other end thereof, said foil generating lift when moved with relative motion through a fluid, said motion inducing variations in pressure on said foil with the tip end producing an associated drag-inducing vortex flow therearound due to the crossflow moving outwardly with respect to the root from the higher pressure surface of the foil toward the lower pressure surface thereof, the improvement comprising, in combination, crossflow capture means at said foil tip, said capture means having a flow intercepting surface comprising a curved capture surface extending at least across the chord of said foil tip and from the upper surface of said foil to below the lower surface thereof, the lower edge of said surface extending inboard of said foil tip, with the concave side of said capture surface facing said foil root and forming a crossflow capture inlet, and aspirating means for removing crossflow captured by said capture surface for venting at a location away from said capture flow inlet, said aspirating means consisting of a fluid stub foil fixedly mounted on the tip of the fluid foil on the low pressure surface side thereof, the flow of fluid over said foil and stub foil generating regions of higher and lower pressures on the surfaces thereof, a slot in said stub foil surface opening on to a low pressure region thereof, a fluid passageway connecting said slot to the crossflow capture inlet such that said slot aspirates the crossflow intercepted by the curved capture surface whereby the crossflow intercepted and removed by said capture and aspirating means weakens the tip vortex core strength to thereby reduce lift-induced drag on said fluid foil.