Anton Flettner's start in the aeronautical industry goes back as far as 1905 when, on finishing his studies, he was employed by Zeppelin on development work into remote-control systems for lighter-than-air craft.
During World War I he perfected his servo-control, the Flettner tab, still in use today on almost every aircraft in the world.
During the 1920s he invented the Flettner rotor, a sort of rotating cylinder producing an aerodynamic force sufficient to move a vessel. The rotors were actually fitted to two ships, the Buchau and the Baden-Baden, on which they were mounted vertically on the top deck.
Flettner first entered the rotary wing field in 1930 by designing a torqueless drive helicopter with which some tethered tests were carried out in 1933, but a gust of wind destroyed this prototype. It had a two-bladed rotor 30 metres in diameter, each blade of which was fitted with a small Anzani 30hp engine. In operation it was quite like Isacco's aircraft.
P.Lambermont "Helicopters and Autogyros of the World", 1958