German inventor of the rotor ship, a vessel propelled by revolving cylinders mounted vertically on the deck. He also invented the Flettner trim-tab control for aircraft and the Flettner marine rudder.

Flettner directed an aeronautical and hydrodynamic research institute in Amsterdam following World War I. In 1926 he established in Berlin an aircraft company that produced the Flettner Fl 282 and other helicopters for the German Luftwaffe (Air Force) during World War II. After the war he went to the U.S., where he conducted helicopter research for the U.S. Army and was president of the Flettner Aircraft Corporation, Kew Gardens, Queens, N.Y.