Jacob Christian Hansen-Ellehammer (born 14 June 1871 in Bakkebølle, died 20 May 1946 in Gentofte) was a Danish inventor and aviation pioneer.

He obtained a total of 59 Danish patents and worked with many different things, including amusement machines, Tivoli boats, egg openers, cleavers for pig slaughterhouses, engines in countless shades, motorcycles, cars, alternative energy and fire-fighting equipment.

The father and his two brothers, Christian and Henrik, took part in the drainage of Vålse Vig using an invented water lift which was driven by a Dutch windmill.

Ellehammer was trained as a watchmaker in Nykøbing Falster and then went to Copenhagen, where he was apprenticed as an electromechanic, which was one of the pioneering jobs of the time.

The initial engine soon proved too weak and homemade cylinders with a larger volume were fitted on an even bigger block.

Ellehammer continued to work on the problem of controlled flight by making a more powerful engine and on reducing the aircraft's weight.

In Kiel, Germany, Ellehammer flew on 28 June 1908 approx 50m and thereby won a prize of 5,000 Mark for the achievement.

Hansen-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 horizontal flight.

An air-cooled two-cylinder engine was combined with a friction gear and drove the drive axle via belts.

[4] The Danish Museum of Science and Technology in Copenhagen permanently exhibits a large number of his inventions.