From 1910 to 1913 a series of, Clerget badged, inline-four and V8 aero-engines were manufactured and marketed by the Clément-Bayard automobile firm.
From 1912, Pierre Clerget focused his efforts on developing a series of rotaryaircraft engines and founded a new company, Clerget-Blin in 1913. During World War I, more than 30,000 Clerget rotary engines were manufactured in France by Clerget-Blin and in Great Britain by Gwynnes Limited. Clerget rotary engines were used on such aircraft as the Sopwith Camel and Vickers Gunbus.
The first Clerget aero engine to enter series production was the 50 hp model introduced in 1910. It was a water-cooled inline-four engine that produced 50hp (37kW) when cold and approximately 40hp (30kW) when running at full operating temperature. The engine had aluminum pistons which contributed to its low weight of 73 kg (161 lb).[1]:106–110 Cylinders were made of steel with water-jackets shaped to form expansion bellows and electroplated with copper. On each of the four cylinders, the pushrod operating the inlet valve was fitted inside a hollow tubular rod which operated the exhaust valve.[2] The engine was used on several pioneering aircraft including the Coandă-1910 and the first Etrich Taube. Clerget also designed a similar, larger inline-four engine that produced 100hp (75kW). Both these engines were manufactured by Clément-Bayard.[1]:106–110
In October 1910, at the Paris Air Show, Clément-Bayard showcased a powerful Clerget water cooled V8 aircraft engine rated at 200hp (150kW).[1]:106–110 Each cylinder bank was of a similar design to Clerget's earlier inline-four models. The engine weighed 290kg (640lb) which gave a power to weight ratio of 0.515kW/kg (0.313hp/lb),[2] considered remarkable for its time period.[3] The engine featured a form of variable valve timing, utilising a camshaft that could be adjusted axially to engage different cam profiles. This allowed the opening period of the intake and exhaust valves to be optimised during flight.[1]:118[2] In 1912, a single 200 hp Clerget engine was fitted to the giant Voisin Icare Aero-Yacht.[1]:110
Early Clerget engine types
200 hp Clerget aircraft engine displayed at the London Science Museum
Cylinder head of a Clerget 9J, showing the two valve rockers and the induction pipe from the rear of the engine
From 1912, Pierre Clerget devoted himself to the design of rotary engines. Clerget's designs were successful, initially with the sports aircraft market and then with military customers. In 1913, Pierre Clerget founded a new company, Clerget-Blin with the industrialist Eugène Blin. More than 30,000 Clerget rotary engine were built during World War I [1]:163 with the type being fitted to a large number of important aircraft including the Sopwith Camel and Vickers Gunbus.[6]
Design features
The Clerget rotary engines were air-cooled with either seven, nine or eleven cylinders. They were fitted with a double thrust ball race, which enabled them to be used either as a pusher or as a tractor engine.[1]:136–137
The engines worked on a four-stroke cycle. The chief point of difference from other rotary engines was that the inlet and exhaust valves were mechanically operated by means of separate cams, tappets and rocker arms.[1]:136–137
A source of failure among the Clerget engines were the special-purpose piston rings, called obturator rings. These were located below the gudgeon or wrist pin, to block heat transfer from the combustion area to the lower part of the cylinder and overcome their subsequent distortion. These rings were often made from brass and only had a lifespan of a few hours. The Bentley BR1 and Bentley BR2 rotaries were designed as improvements of the Clerget, while sharing some of the earlier engine's distinctive design features they had conventional piston rings and cylinder liners.[7]
The Shuttleworth Collection based at Old Warden Aerodrome in the UK, operate an airworthy late production Sopwith Triplane(G-BOCK)[8] fitted with an original 9B as well as an airworthy late production Sopwith Camel(G-BZSC)[9] fitted with an original long-stroke 9Bf. These aircraft can be seen displaying at home air displays through the summer months.
An experimental 420 hp (310 kW) 16-cylinder, four-row X engine. The only non-rotary engine built by Clerget-Blin.[1]:362
Diesel radial engines
A Clerget 14F diesel aircraft engine preserved at the Conservatoire de l'Air et de l'Espace d’Aquitaine
Following the bankruptcy and liquidation of Clerget-Blin in 1920, Pierre Clerget joined the Service Technique de l'Aéronautique (STAé) as an engineer, where he specialised in the study of aircraft diesel engines up until his death in 1943.[1]:225–227
Clerget 9A
(1929) 100hp (75kW) nine-cylinder, single row radial engine.[10]
Clerget 9B
Clerget 9C
Produced under licence by Hispano-Suiza as the Hispano-Suiza 9T
Clerget 14F-01
(1937) 14-cylinder, two-row radial engine, flown in a Potez 25 biplane.
Clerget 14F-02
Clerget 14Fcs
16H engine
Clerget's final engine design was a V-16 designated Clerget 16H and known as the Type Transatlantique. It developed 2,000hp (1,500kW) through the use of four Rateauturbochargers.[1]:366
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