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Armstrong Siddeley Aero-Engines

Whenever the name Armstrong Siddeley is mentioned most people think of motor cars and rather luxurious ones at that, yet this firm also made rather a lot of aero-engines; in fact, it made far more aero-engines than motor cars! The depression that followed the Wall Street crash of 1929 lead to many manufacturers of motor cars going out of business, perhaps more importantly had Armstrong Siddeley concentrated on only producing cars they too would have gone out of business, fortunately, making aero-engines was a very profitable business and Armstrong Siddeley survived.

The Siddeley-Deasy component of Armstrong Siddeley had considerable experience in building aero-engines for the Royal Flying Corps with hundreds of Royal Aircraft Factory designs being delivered by the end of WW1. Perhaps of more importance as a result of the Royal Aircraft Factory ceasing to design and manufacture aero-engines and aircraft S.D. Heron, their principle engine designer joined Siddeley-Deasy bringing with him the design plans of the R.A.F 8 engine. This engine became the highly successful Jaguar air-cooled radial engine that was the world first supercharged aircraft engine.

Many aero engines were produced by Armstrong Siddeley from quite small engines through to jet age versions such as the Sapphire jet engine and the Double Mamba Turboprop engine. Following government intervention, Armstrong Siddeley was merged with Bristol Aero-Engines to become Bristol Siddeley, this firm was later absorbed into Rolls Royce. This section covers the engines built by Armstrong Siddeley up to the time it became part of Bristol Siddeley.

Armstrong Siddeley developed a wide range of air-cooled radial engines that they named after cats which are listed below in an at a glance table; it is intended to produce articles in greater detail of the coming months. Where the engine name is highlighted in blue there is a link to the full description.


An air-cooled 14-cylinder two-row normally aspirated radial engine first developed in 1922. There were several different versions including a supercharged version.


A small radial engine that used two-cylinders of the Jaguar engine.


A development of the Jaguar, initially known as the Jaguar Major, 27-litre 14-cylinder radial engine.


A further development of the Jaguar engine produced in the 1930s and was the first British aero-engine to use a two-stage supercharger.


A seven-cylinder air-cooled radial aero-engine that was in fact half of a Jaguar engine.


A development of the Lynx engine, initially known as the Lynx Major, with an increased bore but the same stroke as the Lynx. The Cheetah remained in production from 1935 to 1948. It was the first engine of its type to be certified for 1,200 hours of operational time between overhauls (TBO), with over 37,200 examples built.


A five-cylinder, air-cooled, radial engine that was first run in 1926, it was a popular light aircraft power plant.

Genet Major

A Genet with an increased bore and stroke.


The RAF version of the Genet Major.


A five-cylinder air-cooled radial engine first developed in 1926, it had an unusual configuration with the fifth cylinder at the bottom of the engine.


A development of the Mongoose, initially known as the Double Mongoose, with a double row of ten cylinders.


 A nine-cylinder single row air-cooled radial engine developed in 1945, one engine was tested but it did not go into production.


A 14cylinder single row air-cooled radial engine developed in 1927 and whilst it was the most powerful radial engine at the time it was only produced in limited quantities.


There was also a range of engines name after breeds of dogs, these were mainly triple row radial engines, there were difficulties developing these engine and following the Coventry Blitz in WW2, the British government ordered that all work on this range of engines should be halted as they could not be expected to enter into production in the foreseeable future.

The names given to these engines included, Deerhound, Hyena, Mastiff, Terrier, Wolfhound and Boarhound; for a full description click here.

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