De Havilland Gipsy - Design and Development - Cirrus Origins

Cirrus Origins

In 1925 Geoffrey de Havilland was looking for a reliable cheap engine for use in a light sports aircraft. More particularly, he was looking for something like his favourite World War I aircraft engine: the 240 hp (180 kW) Renault 8G air-cooled V8, but with half the weight and half the power. Halford gave it to him by building a four-cylinder crankcase and adding to it half of the Renault's cylinders, several other of the Renault’s components, and standard parts used in car engines. The result was a 60 hp (45 kW) in-line aircraft engine that, although it fell short of the promised horse-power, was still superior to all contemporary engines for light aircraft. Most importantly it was a true aircraft engine at a time where its competitors were more often than not motorcycle engines adapted to running at high altitude. The engine secured, de Havilland Aircraft commenced manufacture of the D.H.60 Moth and the combination of reliable powerplant - the ADC Cirrus - and reliable training craft – the Moth - marked the start of serious sports flying in Britain.

By 1927 however, the Moth threatened to become a victim of its own success as continuing demand was depleting the stockpiles of surplus Renaults needed to build its Cirrus engine. The Moth now having provided a solid financial cushion, de Havilland Aircraft decided to take the problem head-on and start its own engine factory. Geoffrey de Havilland again went to his old friend Halford and this time asked him to design a completely new aircraft engine of weight and performance comparable to the latest version of the Cirrus, the 105 hp (78 kW) Cirrus Hermes.