Anton Flettner pioneered rotating-wing aircraft. In 1932 tested machine with engine/propeller on each main rotor blade. Formed Flettner GmbH 1935, built Fl 184 autogyro, Fl 185 operable as autogyro or helicopter and Fl 265 helicopter with 2 intermeshing 'eggbeater' rotors (6 for German navy 1939—40). Led to Fl 282 Kolibri, first mass-produced helicopter in world (24 in service 1943, 1,000 ordered but factories bombed).

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