Patent ID: 8215897

Claim:
A vertical windmill comprising: at least one airfoil continuously rotatable about a vertical axis in a direction of rotation, said airfoil having a nosepiece at a leading end and a tail comprising a wedge-shaped trough at a trailing end, said windmill including means for supporting said airfoil so that it travels in a circular path in a horizontal plane about said axis; said airfoil including aerodynamic surfaces for being driven by wind through four different phases of rotation relative to a wind direction, said phases occurring approximately 90 degrees apart within each 360 degrees of travel of said airfoil about said axis; a first phase of rotation wherein said airfoil travels laterally across said wind direction during which a forward net driving force is exerted on the airfoil by the wind in a first lateral direction of travel; a second phase of rotation during which said airfoil travels downwind in the direction of said wind and is driven forward by the force of air captured by the wedge-shaped trough of the tail and rearward facing surfaces on the leading end of said airfoil; a third phase of rotation in which said airfoil travels laterally across said wind direction in a second lateral direction of travel opposite the direction of travel during said first phase whereby a net forward driving force is exerted on the airfoil by the wind in the second lateral direction of travel; and a fourth phase of rotation during which said airfoil travels directly against the wind whereby a small retarding force relative to the net forces produced during the other phases of rotation is exerted on the airfoil by the wind.