A start is made by considering why the subsonic propeller was abandoned when aircraft speeds approached the shock stall. It is true that the shock stall also occurs on the propeller blades under these conditions, causing a loss of lift and an increase of drag, but this is not the predominant effect which produces the marked decrease of propeller efficiency associated with high-speed aircraft. The main aerodynamic difficulty associated with the shock stall on the wings of an aircraft is due to the separation of flow caused by the shock wave rather than the presence of the shock wave itself. This difficulty is reduced on a propeller, as any separation of flow which might occur on a propeller blade due to the shock stall, would tend to cause the air to be stagnant relative to the blade, and would thus experience a large centrifugal force by virtue of the propeller rotation. Thus the propeller shock stall would never develop to the same degree that it does on the wings of an aircraft in steady flight.