Patent ID: 7497403

Claim:
A method for providing a foil, comprising: (a) providing a foil having an inward portion, a tip, a chordwise direction, a relatively higher pressure foil surface, a relatively lower pressure foil surface, a leading edge and a trailing edge, said foil having relative movement to a fluid medium that is arranged to permit said foil to experience lift generation that produces a foil lifting force on said foil having a direction that is substantially from said relatively higher pressure surface toward said relatively lower pressure surface, said tip having a tendency to create an induced drag vortex within said fluid medium in the wake behind said foil; and (b) providing a vortex generator connected to said foil near said tip, said vortex generator having a substantially streamwise alignment, said vortex generator being arranged to generate a counter vortex within said fluid medium in said wake behind said vortex generator that has a direction of spin that is opposite of said induced drag vortex, said vortex generator having a relatively lower pressure generator surface and a relatively higher pressure generator surface that are arranged to create a predetermined generator lifting force on said vortex generator, said vortex generator being oriented to substantially avoid creating a significant reduction in said foil lifting force on said foil during said lift generation, said substantially streamwise alignment being at an angle to said chordwise direction to generate said counter vortex; (c) adjusting said substantially streamwise alignment to control the strength of said counter vortex so as to create a reduction in the strength of said induced drag vortex.