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09/30/2007. Dr. Friedrich von Doblhoff invented the helicopter with a rotor powered by ramjets mounted at the rotor tips. With the help of Dr. August Stepan and Theodor Laufer a series of helicopters was build at the Wiener Neustädter Flugzeugwerke (also known as WNF) in Vienna, Austria. The four different prototype helicopters were designated WNF-342 V1 to V4. The pictured fourth prototype used the ramjets at the rotor tips for take-off, hovering and landing only. An 140hp Siemens-Halske Sh.14A radial engine drove a conventional pusher propeller for forward flight while the rotor blades 'free-wheeled' in autorotation pitch. The side-by-side two-seater was first flown early in 1945 and captured by US forces in April of the same year. It was transferred to the USA for testing, where Dr. von Doblhoff provided assistance.