De Havilland Gipsy Six

Gipsy Six
Preserved Gipsy Six
Type	Piston inline aero engine
Manufacturer	de Havilland Engine Company
First run	1935
Major applications	de Havilland Dragon Rapide
Number built	1,139
Developed from	de Havilland Gipsy Major
Developed into	de Havilland Gipsy Queen

The de Havilland Gipsy Six is a British six-cylinder, air-cooled, inverted inline piston engine developed for aircraft use in the 1930s. It was based on the cylinders of the four-cylinder Gipsy Major and went on to spawn a whole series of similar aero engines that were still in common use until the 1980s.

The engines were of particular note for their exceptionally low cross-sectional area, a drag-reducing feature which made them ideal for the many racing aircraft of that period. In 1934, the basic bronze-headed Gipsy Six, rated at 185 horsepower (138 kW) at 2,100 rpm was modified for use in the DH.88 Comet air racer as the Gipsy Six "R" which produced 223 horsepower (166 kW) at 2,400 rpm for takeoff. Many Gipsy Six engines remain in service powering vintage aircraft types today.

The de Havilland company had hoped to produce a version of the basic engine capable of utilising a hydraulically actuated variable-pitch (VP) airscrew based on the American Hamilton "Bracket-Type" in time for the 1934 MacRobertson Race. Since there was so little time to perfect this installation, as a compromise, a French "Ratier" VP airscrew was fitted to the Comets' "R" engines, which utilised a simple air-filled bladder for a once-per-flight automatic pitch change. Later on, Comets were fitted with the Series II engine, which eliminated this crude system. Power for the "R" was increased to a takeoff rating of 223 horsepower (166 kW) by increasing the compression ratios from 5.25:1 to 6.5:1, while fitting aluminium alloy cylinder heads, domed-pistons and modified valve gear. Production of the basic fixed-pitch Gipsy Six unit began in 1935, with the engines rated at 200 horsepower (150 kW) at 2,400 rpm for takeoff.

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