1914 photo of Ellehammer's coaxial helicopter hovering
Following the end of his apprenticeship as a watchmaker he moved to Copenhagen where he worked as an electronics mechanic before establishing his own company in 1898. In the beginning he produced cigarette machines, beverage machines and other electronic machinery. In 1904 he produced his first motorcycle, the Elleham motorcycle. In 1905, he constructed a monoplane, and in the following year a "semi-biplane". In this latter machine, he made a tethered flight on 12 September 1906.
1935 photo of Ellehammer's disc-rotor compound helicopter model
Ellehammer's later inventions included a successful triplane and helicopter. His helicopter was a coaxial machine. A famous photo shows it hovering in 1914, though there is no evidence that it was successful in achieving translational flight. Ellehammer later studied a disc-rotor configuration - a compound helicopter with coaxial blades that extended from the hub for hover, and retracted for high speed vertical flight. Although a wind tunnel model was constructed, there's no evidence that anything more was studied.