Clerget was the name given to a series of early rotary

aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...

types of the

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

era that were designed by Pierre Clerget. Manufactured in France by

Clerget-Blin Clerget-Blin (full name being ''Société Clerget-Blin et Cie'') was a French precision engineering company formed in 1913 by the engineer and inventor Pierre Clerget and industrialist Eugène Blin. In 1939, the company was absorbed into the ''G ...

and in Great Britain by Gwynnes Limited they were used on such aircraft as the

Sopwith Camel The Sopwith Camel is a British First World War single-seat biplane fighter aircraft that was introduced on the Western Front in 1917. It was developed by the Sopwith Aviation Company as a successor to the Sopwith Pup and became one of the b ...

and

Vickers Gunbus The Vickers F.B.5 (Fighting Biplane 5) (known as the "Gunbus") was a British two-seat pusher military biplane of the First World War. Armed with a single .303 in (7.7 mm) Lewis gun operated by the observer in the front of the ...

. In the 1920s Pierre Clerget turned his attention to

diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...

s and finally produced a H-16 engine before he died in 1943.

Rotary engine development (spark ignition)

Clerget 9 engine, cylinder head and valve rockers

What distinguished the Clerget rotary engine from its rivals (

Gnome A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its characte ...

and Le Rhône) was that the Clerget had normal intake and exhaust valves unlike the Gnome, and the

connecting rod A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the cranksh ...

arrangement was much simpler than the Le Rhone. A source of failure among the Clerget engines were the special-purpose piston rings, called

obturator ring An obturator ring was a type of piston ring used in World War I aircraft engines, aero engines for improved sealing in the presence of Cylinder (engine), cylinder distortion. Purpose The cylinders of Rotary engine, rotary aircraft engines of Worl ...

s. These were located below the

gudgeon A gudgeon is a socket-like, cylindrical (i.e., ''female'') fitting attached to one component to enable a pivoting or hinging connection to a second component. The second component carries a pintle fitting, the male counterpart to 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 Clerget engines were considered reliable but they cost more per unit to produce than their rivals. Unlike other contemporary rotaries in which the ignition system was either switched on or off to provide a rudimentary form of engine speed control, the Clerget featured a

throttle A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ...

. The

Bentley BR1 The Bentley BR.1 was a British rotary aircraft engine of the First World War. Designed by the motor car engine designer W. O. Bentley, the BR.1 was built in large numbers, being one of the main powerplants of the Sopwith Camel. Design and develo ...

and Bentley BR2 rotaries were designed as improvements of the Clerget, while sharing some of the earlier engine's distinctive design features.

Design features

The Clerget rotary engines were

air-cooled Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. In all combustion engines, a great percentage of the heat ge ...

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 A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...

engine. The engines worked on a four-stroke cycle. The chief points of difference from other rotary engines were: * The pistons were of an

aluminium alloy An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal ...

. * The connecting rods had a tubular section. * The inlet and exhaust valves were mechanically operated by means of separate cams,

tappet A tappet is most commonly a component in an internal combustion engine which converts the rotating motion of the camshaft into linear motion of the valves, either directly or indirectly. An earlier use of the term was for part of the valve gear ...

s and

rocker arm In the context of an internal combustion engine, a rocker arm is a valvetrain component that typically transfers the motion of a pushrod to the corresponding intake/exhaust valve. Rocker arms in automobiles are typically made from stamped steel ...

s. The direction of rotation was counter (anti)-clockwise as seen from the propeller-end of the engine. Between any two consecutive firing strokes, the engine turned through 80 degrees. Like many other rotary engines of the period they were made chiefly of steel, for strength and lightness.

Rotary engine types

; Clerget 7Y :(1912) , seven-cylinder. ; Clerget 7Z :(1911) , seven-cylinder. ;

Clerget 9A Clerget was the name given to a series of early rotary aircraft engine types of the World War I era that were designed by Pierre Clerget. Manufactured in France by Clerget-Blin and in Great Britain by Gwynnes Limited they were used on such airc ...

:(1914) , nine-cylinder derivative of 7Z. (designation reused for radial) ;

Clerget 9B The Clerget 9B was a nine-cylinder rotary aircraft engine of the World War I era designed by Pierre Clerget. Manufactured in both France and Great Britain (Gwynnes Limited), it was used on such aircraft as the Sopwith Camel. The Clerget 9Bf was ...

:(1915) , nine-cylinder. (designation reused for radial) ;Clerget 9Bf :(1915) , nine-cylinder long stroke version of the Clerget 9B. The most numerous British production engine with 2,350 units being built. ;Clerget 9J :(1917) , nine-cylinder. Redesigned with aluminium pistons, tubular connecting rods and revised valve gear. ;Clerget 9Z :(1915) , nine-cylinder. ; Clerget 11Eb :(1918) , 11-cylinder, single-row engine.

Rotary engines on display

*A locally-built Clerget 9B of 1917 is displayed at the

Museum of Lincolnshire Life The Museum of Lincolnshire Life is a museum in Lincoln, Lincolnshire, in the UK. The museum collection is a varied social history that reflects and celebrates the culture of the county of Lincolnshire and its people from 1750 to the present day ...

. *A preserved Clerget 9B engine is on public display at the

Fleet Air Arm Museum The Fleet Air Arm Museum is devoted to the history of British naval aviation. It has an extensive collection of military and civilian aircraft, aero engines, models of aircraft and Royal Navy ships (especially aircraft carriers), and paintin ...

, RNAS Yeovilton.

Operational rotary engines

The Shuttleworth Collection The Shuttleworth Collection is a working aeronautical and automotive collection located at the Old Warden Aerodrome, Old Warden in Bedfordshire, England. It is the oldest in the world and one of the most prestigious, due to the variety of old a ...

based at

Old Warden Aerodrome Old Warden Aerodrome is located east southeast of Bedford, in Bedfordshire, England. The privately owned aerodrome serves The Shuttleworth Collection The Shuttleworth Collection is a working aeronautical and automotive collection located ...

in the UK, operate an airworthy late production Sopwith Triplane ''(G-BOCK)'' fitted with an original 9B as well as an airworthy late production

''(G-BZSC)''The Shuttleworth Collection - Sopwith Camel
Retrieved: 21 August 2018 fitted with an original long-stroke 9Bf. These aircraft can be seen displaying at home air displays through the summer months.

Radial 'X' engines

;Clerget 16X :A 420 hp (310 kW) 16-cylinder, four-row

X engine An X engine is a piston engine with four banks of cylinders around a common crankshaft, such that the cylinders form an "X" shape when viewed from front-on. The advantage of an X engine is that it is shorter than a V engine of the same number o ...

Diesel radial engines

In the 1920s Pierre Clerget designed static

s, the earliest were based on his rotary designs. ;Clerget 9A: (1929) 100 hp (75 kW) Nine-cylinder, single row radial engine. ;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 Potez 25 (also written as Potez XXV) was a French twin-seat, single-engine biplane designed during the 1920s. A multi-purpose fighter-bomber, it was designed as a line aircraft and used in a variety of roles, including fighter and escort mission ...

biplane. ;;Clerget 14F-02: ;;Clerget 14Fcs:

H-16 engine

Clerget's final engine design was an H-16 known as the Type Transatlantique. It developed 2,000 hp (1,500 kW) through the use of four

turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

References

* "Air Board" Technical Notes issued by Controller Technical Department for persons holding an official position in His Majesty's Service dated 1918 * *

External links

Image and description of aClerget 9B rotary engineA Clerget-Blin 9Bf, Gwynnes Ltd, at Powerhouse Museum, Sydney, AustraliaClerget engine details and type listings (French)
{{Clerget aeroengines Air-cooled aircraft piston engines 1910s aircraft piston engines Rotary aircraft piston engines Aircraft radial diesel engines