Jacob Christian Hansen-Ellehammer (1871-1946) was a prolific Danish inventor and skilled engineer who filed for over 400 patents during his lifetime. On 12 September1906, Ellehammer made a short flight covering a distance of 42 meters (128 feet) in an airplane of his own design, although the aircraft had control only in pitch and was tethered to follow a circular flight path. By 1908, Ellehammer constructed an improved biplane, making short, free flights near the ground, mostly all in a straight line. A more refined monoplane followed this design, although its performance was still limited. In 1910, Ellehammer diverted his attention to the development of a helicopter and by September 1911 had constructed a 1/3-scale flying model of his proposed coaxial rotor design. From 1912-16, Ellehammer's full-scale helicopter made many piloted flights, mostly short hops, hovering close to the ground and flying slowly forward, all with reasonable stability. Ellehammer's helicopter design is technically significant in that it was the first to incorporate collective and cyclic blade pitch control, and it was also the first to be powered by an air-cooled radial engine. Ellehammer continued with his research into vertical flight aircraft for another two decades, patenting a convertiplane design in 1926 and a disk-rotor concept in 1936, but his designs never came to practical fruition.
Collins. A, Leishman. J (2011). The Aeronautical Exploits of Jacob Ellehammer.
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