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. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbin ...

types of the

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

era that were designed by Pierre Clerget( fr). 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 '' ...

and in Great Britain by

Gwynnes Limited Gwynnes Limited was a City of London England engineering business, iron founders and pump makers founded in 1849 to capitalise on the centrifugal pump inventedThe first practical centrifugal pump called the Massachusetts pump was built in the Uni ...

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. 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 engine ...

radial engine The radial engine is a reciprocating engine, reciprocating type internal combustion engine, internal combustion engine configuration in which the cylinder (engine), cylinders "radiate" outward from a central crankcase like the spokes of a wheel. ...

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

Rotary engine development (spark ignition)

What distinguished the Clerget rotary engine from its rivals (

Gnome A gnome () is a mythological creature and diminutive spirit in Renaissance magic and alchemy, introduced by Paracelsus in the 16th century and widely adopted by authors, including those of modern fantasy literature. They are typically depict ...

and

Le Rhône Le Rhône was the name given to a series of Rotary engine, rotary aircraft engines built between 1910 and 1920. Le Rhône series engines were originally sold by the Gnome et Rhône#Le Rhône, Société des Moteurs Le Rhône and, following a 1914 ...

) was that the Clerget had normal intake and exhaust

valves A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, ...

unlike the Gnome, and the

connecting rod A connecting rod, also called a 'con rod', is the part of a reciprocating engine, piston engine which connects the piston to the crankshaft. Together with the crank (mechanism), crank, the connecting rod converts the reciprocating motion of the p ...

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

piston ring A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine. The main functions of piston rings in engines are: # Sealing the combustion chamber so that there is mini ...

s, called obturator rings. 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 Ignition systems are used by heat engines to initiate combustion by igniting the fuel-air mixture. In a spark ignition versions of the internal combustion engine (such as petrol engines), the ignition system creates a spark to ignite the fuel-ai ...

was either switched on or off to provide a rudimentary form of engine speed control, the Clerget featured a

throttle A throttle is a mechanism by which fluid flow is managed by construction 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'' ha ...

. The Bentley BR1 and

Bentley BR2 The Bentley B.R.2 was a nine-cylinder British rotary aircraft engine developed during the First World War by the motor car engine designer W. O. Bentley from his earlier Bentley BR.1. The BR.2 was built in small numbers during the war, its mai ...

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. Air-cooled designs are far simpler than their liquid-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 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 (vehicle), trailer or machinery such as that used in agriculture, mining or constructio ...

engine. The engines worked on a

four-stroke cycle A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directio ...

. The chief points of difference from other rotary engines were: * The connecting rods had a tubular section. * The inlet and exhaust valves were mechanically operated by means of separate

cam Cam or CAM may refer to: Science and technology * Cam (mechanism), a mechanical linkage which translates motion * Camshaft, a shaft with a cam * Camera or webcam, a device that records images or video In computing * Computer-aided manufacturin ...

tappet A tappet or valve lifter is a valve train component which converts rotational motion into linear motion in activating a valve. It is most commonly found in internal combustion engines, where it converts the rotational motion of the camshaft into ...

s and

rocker arm A rocker arm is a valvetrain component that typically transfers the motion of a pushrod in an overhead valve engine, overhead valve internal combustion engine to the corresponding intake/exhaust poppet valve, valve. Rocker arms in automobiles are ...

s. The direction of rotation was counter (anti)-clockwise as seen from the propeller-end of the engine. Like many other

rotary engine The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and its ...

s of the period they were made chiefly of steel, for strength and lightness.

Rotary engine types

; Clerget 7Y :(1912) , seven-cylinder. ; Clerget 7Z :(1913) , seven-cylinder. ;Clerget 9A :(1913) , nine-cylinder derivative of 7Z. (designation reused for radial) ;

Clerget 9B The Clerget 9B is a nine-cylinder rotary engine, 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 Cler ...

:(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 da ...

. *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 paintings ...

RNAS Yeovilton Royal Naval Air Station Yeovilton, commonly referred to as WAFU central, (HMS ''Heron'') is an airbase of the Royal Navy, sited a few miles north of Yeovil, in the English county of Somerset. It is one of two active Fleet Air Arm bases, the ...

Operational rotary engines

The Shuttleworth Collection The Shuttleworth Collection is a working aviation, automotive and agricultural collection located at Old Warden Aerodrome in Bedfordshire, England. History The collection was founded in 1928 by aviator Richard Ormonde Shuttleworth. While fl ...

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, which contains a large working collection of vintage aircraft, cars, motor cycles and agricu ...

in the UK, operate an airworthy late production

Sopwith Triplane The Sopwith Triplane is a British single seat fighter aircraft designed and manufactured by the Sopwith Aviation Company during the First World War. It has the distinction of being the first military triplane to see operational service. The T ...

''(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 front-on. The advantage of an X engine is that it is shorter than a V engine of the same number of c ...

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 sesquiplane designed during the 1920s. A light multi-purpose Strike fighter, fighter-bomber, it was designed as a line aircraft and used in a variety of roles, including F ...

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 2,000 hp (1,500 kW) through the use of four Rateau

turbocharger In an internal combustion engine, a turbocharger (also known as a turbo or a turbosupercharger) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into th ...

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