U.S. Patent Specifications

In a vehicle power plant comprising a pair of coaxial controllable‐pitch propellers and means for rotating said propellers independently in opposite directions, means for holding one of said propellers against rotation, and means for turning the blades of the propeller so held to a pitch position at which aerodynamic forces acting on said propeller during flight tend to turn said propeller in the same direction as the direction of rotation of the other propeller.