Grace's Guide

British Industrial History

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Clerget 4-cylinder aero engine at Vienna Technical Museum. 4.6 litres, 50 HP at 1600 rpm. It powered the first Etrich-Traube. The museum's sign gives a date of 1909
Clerget aero engine at Vienna Technical Museum, showing details of cylinder head. Inlet and exhausr valves are actuated by coaxial pushrods
1910. 200hp 8-cylinder engine.
c.1911 Clerget 200 HP V8 engine at the London Science Museum
c.1911 engine at the London Science Museum
1910. Monoplane.
November 1912.
Type 9B. 130 hp. 16.29 litres. Exhibit at the Fleet Air Arm Museum.
Type 9B. 130 hp. 16.29 litres. Exhibit at the Fleet Air Arm Museum.

Pierre Clerget (1875 - 1943) was a French mechanical engineer, inventor and industrialist. He devoted himself to the design and development of aircraft engines.

1892 He produced a single-cylinder variable compression engine for experimental purposes.

1901 Clerget produced 4-cylinder petrol engines in conjunction with Laurent and Collot.

From 1905, Pierre Clerget designed engines manufactured by Clément-Bayard.

1911 Clerget developed a 4-cylinder engine of 100 hp for airships, then a 200 HP 60-degree V-8 engine with a high power-weight ratio, produced by Clément-Bayard. The V-8 was used by Gabriel Voisin for his 1912 seaplane.

1913 Clerget joined forces with the industrialist Eugène Blin and founded Clerget-Blin at 37 rue Cavé in Levallois-Perret, using the premises of Malicet-Blin and started to produce 7 and 9-cylinder rotary aero engines. Unlike the Gnome engines, the Clerget engines used conventional valves actuated by pushrods, for greater efficiency. They were cheaper than the two rotary competitors, the 9-cyl Gnome and the 9-cyl Le Rhône, and the engine was reliable and durable. The Clerget did not suffer the problems of its competitors - a fragile automatic valve opening device on the Gnome, and a vulnerable fuel supply system on the LeRhône engine. The engine's qualities were soon appreciated by Sopwith.

The best-known Clerget air-cooled rotary engine had nine cylinders, 120 mm by 160 mm, and was rated at 110 hp (82 kW), but capable of developing 130 hp (97 kW) at 1,200 rpm. It was fitted with a double thrust ball race, and could be used either as a pusher or as a tractor. Like many other radial engines it was made chiefly of steel. Its chief points of difference from other rotary engines were:

  • Aluminium alloy pistons.
  • The connecting rods had a tubular section.
  • The inlet and exhaust valves were mechanically operated by means of separate cams, tappets and rocker arms.


  • Approx oil consumption: 2 imp gal/h (9 L/h)
  • Approx petrol consumption: 10 imp gal/h (45 L/h)
  • Approx weight of engine: 365 lb (166 kg), i.e. 3.3 lb per rated hp (2 kg/kW) (0.36hp/lb)

Sopwith Aircraft used the Clerget 9A on a large scale, followed by the 9B.

The 7 and 9 series Clerget-Blin rotary engines were also produced in Britain by Gordon Watney (Weybridge), Gwynnes (Hammersmith), Ruston Proctor (Lincoln), and Humber-Bentley (Coventry).

Several British engineers, including Walter Owen Bentley, improved the engines. Bentley addressed overheating problems by various means, including the use by Bentley of aluminium pistons. The British engines would consumed less than 25 litres of petrol per hour, compared to more than 35 in competing engines, and six to seven litres of oil per hour, half that of the competitors.[1]

Pierre Clerget developed a diesel 9A in 1929, 9B in 1930, and 9C in 1932, followed by the 14-cylinder 14D and in 1934 the 400 HP 14E, followed by the 14F, capable of developing 450 HP.

In 1917, Clerget produced a non-rotary 400 HP 16-cylinder X-form engine of c.35 litres.

1922 Clerget produced a diesel engine with variable compression (compression rate varying from 4 to 14). In 1925, he produced a two-stroke V8 diesel engine developing 300 HP. The following year, he produced a four-stroke V8 Diesel which developed 60 hp.

In 1928, he designed a 9-cylinder four-stroke diesel engine that developed 100 hp for a weight of 195 kg.

In 1933, Clerget designed a new series of 14-cylinder double-row engines.

In December 1937, the Clerget-powered Potez 25 broke a world altitude record, piloted by Georges Détré, with STAé engineer Raymond Marchal, reaching 7,655 metres.

The Clerget 14 F2 engine passed homologation in 1938 with an output of 520 HP. It was licensed to Panhard-Levassor and Hispano-Suiza.

In 1938, Clerget embarked on the development of high-power diesel engines of 2,000 hp and more, for applications including aircraft, naval and railway use. The Clerget type 16 H engine was an 81-litre V16 turbocharged diesel developing 1,600 hp at 1,800 rpm.

When France fell in WW2, Pierre Clerget refused to collaborate and took refuge in Moissac. He was found dead in 'obscure circumstances' in the Garonne Canal in Moissac in 1943.

Much of the above information is condensed from 'Les moteurs Clerget - Le génie de la mécanique' by Gérard Hartmann. This source includes many illustrations, and also tables of the various engines designed by Pierre Clerget.[2]

See Also


Sources of Information

  1. [1] Les moteurs Clerget, p.10
  2. [2] 'Les moteurs Clerget - Le génie de la mécanique', by Gérard Hartmann
  • [3] Wikipedia
  • [4] Wikipedia - Pierre Clerget (in French)
  • [5] Les moteurs Clerget - Le génie de la mécanique by Gérard Hartmann