Side propellers for the propulsion of fast boats and aircraft

Claim 1

A propeller for providing forward thrust to a body traveling at relatively high speed through a surrounding fluid medium, comprising: (a) a propeller hub having an axis of rotation; (b) a plurality of airfoil surfaces mounted to and distributed radially about said hub;the position of each said airfoil surface being defined by first and second pitch angles, respectively, said first pitch angle being the angle in the rotation direction between the profile longitudinal axis of said airfoil surface and a tangent on the circular arc described by the rotation of said airfoil surface about said propeller hub, and said second pitch angle being the angle between the profile transversal axis of said airfoil surface and said axis of rotation; (c) each airfoil surface having a pivot connection in the region of said hub so that said airfoil surfaces are pivotable about said pivot connections between, on the one hand, an outwardly unfolded condition in which said blades are at a relatively large angle with respect to the hub axis and in which outer ends of said airfoil surfaces are disposed at relatively great distances from the hub axis and, on the other hand, an inwardly folded condition in which said airfoil surfaces are at a relatively small angle with respect to said hub axis and in which said outer ends of said airfoil surfaces are disposed at a relatively small distance from the hub axis; (d) said second pitch angle being relatively large when said airfoil surfaces are in their outwardly unfolded condition, said second pitch angle being relatively small when said airfoil surfaces are in their inwardly folded condition; (e) means for modifying said second pitch angle while said propeller is rotating by opening and folding the propeller by pivoting each airfoil surface, whereby said propeller will operate predominately as a conventional screw-type propeller for operation at low traveling speed through said fluid medium when said second pitch angle is large, and said propeller will provide greater efficiency at high traveling speeds than a conventional screw-type propeller when said second pitch angle is relatively small.