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Jacob Christian Hansen Ellehammer (June 14, 1871 – May 20, 1946) was a Danish watchmaker and inventor, born in Bakkebølle, Denmark. He is remembered chiefly for his contributions to powered flight.
He served an apprenticeship as a watchmaker, before starting his own company in 1898, making a variety of machines, including cigarette-making machines
In 1904 he designed and started manufacturing the 'Elleham' motorcycle.
In 1903–1904 Ellehammer built what is said to be the world's first air-cooled radial aero engine, utilizing three Peugeot Frères cylinders and heads and a home-cast crankcase. This was a failure, and he then successfully adopted larger home-made cylinders and a bigger crankcase. The first functioning radial engine still exists and is displayed at the Danish Museum of Science and Technology at Helsingör. This museum displays an extensive collection of Ellehammer artefacts.
Ellehammer conducted flying experiments, unaware of the Wright brother's first flight in December 1903.
In 1905, he constructed a monoplane, and in the following year a "semi-biplane". Count Knuth Knuthenberg funded the construction of a 300m diameter circular test track on the island of Lindholm, where numerous experiments were undertaken with the aircraft tethered to a central tower. Ellehammer's tethered aircraft with a 9 HP engine was able to rise without the weight of a pilot. The wing area was increased, and an 18 HP engine installed, and on 12 September 1906 the piloted plane succeeded in flying a distance of 42 metres, reaching an altitude of just 0.5m.
Ellehammer moved on to untethered flying, travelling 175m on 14 January 1908, in a tractor triplane powered by his own 36 HP engine. On 13 February 1908 he covered 300m. In June 1908 in Kiel he made short hops of up to 100m., and won 5,000 marks for a flight lasting 11 seconds.
Ellehammer later built a 'coaxial' helicopter. A photo shows it hovering in 1914, though there is no evidence that it was successful in achieving horizontal flight.
Photo of 50 HP 6-cylinder radial engine in workshop here.
The engine shown in photo 1 above was an experimental 1932 3-cylinder, 2-stroke. Bore: 135 mm. Stroke length: 150 mm. Stroke volume: 6.4 litres, approx. 115 HP.