Clerget aircraft engines

Clerget-Blin
Company type	Private company
Industry	Aerospace engineering, Aircraft engines
Founded	1913
Founder	Pierre Clerget, Eugène Blin
Defunct	1920
Fate	Bankruptcy
Headquarters	France
Products	Aircraft engines (inline-four, V8, rotary, radial diesel)

Clerget denotes a series of aircraft engines developed by French engineer Pierre Clerget during the early 1900s.

Between 1910 and 1913, the Clément-Bayard automobile firm manufactured Clerget-branded inline-four and V8 aero-engines. Beginning in 1912, Clerget shifted his attention toward rotary aircraft engines, establishing Clerget-Blin in 1913. Throughout World War I, more than 30,000 Clerget rotary engines were produced in France and Great Britain (the latter by Gwynnes Limited), powering notable aircraft such as the Sopwith Camel and Vickers Gunbus.

Following the bankruptcy of Clerget-Blin in 1920, Pierre Clerget joined the Service Technique de l'Aéronautique (STAé), where he worked on diesel radial engines and an H-16 configuration until his death in 1943.

Early Clerget engines (inline-four and V8)

The initial series-produced Clerget aero engine was a water-cooled inline-four delivering 50 hp, introduced in 1910. It generated 50 hp when cold and approximately 40 hp at normal operating temperatures, utilizing aluminum pistons to reduce weight to 73 kg. The cylinders were constructed from steel with copper-electroplated water jackets. An innovative valve actuation system employed pushrods housed within hollow tubular rods. This engine powered early models such as the Coandă-1910 and the first Etrich Taube. Additionally, a larger 100 hp inline-four variant was produced by Clément-Bayard.

At the October 1910 Paris Air Show, Clément-Bayard showcased a robust Clerget water-cooled V8 engine rated at 200 hp. Weighing 290 kg, it exhibited an impressive power-to-weight ratio for that era. The engine incorporated adjustable camshaft technology that allowed variable valve timing to enhance intake and exhaust valve operation during flight. In 1912, a single 200 hp Clerget engine powered the enormous Voisin Icare Aero-Yacht.

Early Clerget engine variants

Clerget 50 hp: (1910), , inline-four
Clerget 100 hp: (1910), , inline-four
Clerget 200 hp: (1910), , V8

Early Clerget engines preserved

A 50 hp Clerget engine is part of the collection at the Vienna Museum of Science and Technology.
A 200 hp Clerget engine is exhibited at the London Science Museum.

Development of rotary engines (spark ignition)

Starting in 1912, Pierre Clerget concentrated on designing rotary engines, initially aimed at sports aircraft before expanding into military applications. In 1913, he partnered with industrialist Eugène Blin to establish Clerget-Blin. During World War I, over 30,000 Clerget rotary engines were manufactured, powering prominent aircraft including the Sopwith Camel and Vickers Gunbus.

Technical characteristics

Clerget rotary engines were air-cooled and came in seven-, nine-, or eleven-cylinder configurations, featuring a double thrust ball bearing that permitted use in both pusher and tractor aircraft layouts.

Operating on a four-stroke cycle, these engines were distinguished by mechanically actuated inlet and exhaust valves driven through separate cams, tappets, and rocker arms.

A particular challenge was posed by brass obturator piston rings located beneath the wrist pin designed to minimize heat transfer and distortion; however, these rings had a limited lifespan of only a few hours. Subsequent designs such as the Bentley BR1 and BR2 enhanced this concept by adopting conventional piston rings and cylinder liners while preserving certain original design principles.

Varieties of Rotary Engines

Clerget 7Y: (1912) , featuring seven cylinders.
Clerget 7Z: (1913) , equipped with seven cylinders.
Clerget 9A: (1913) , a nine-cylinder model derived from the 7Z. (note: designation later reassigned to a radial engine)
Clerget 9B: (1915) , nine-cylinder configuration. (designation later reused for radial engines)
Clerget 9Bf: (1915) , a nine-cylinder long stroke variant of the Clerget 9B. This was the most widely manufactured British engine, with 2,350 units produced.
Clerget 9J: (1917) , nine-cylinder engine featuring aluminium pistons, tubular connecting rods, and updated valve mechanisms.
Clerget 9Z: (1915) , nine-cylinder design.
Clerget 11Eb: (1918) , an 11-cylinder single-row engine.

Exhibited Rotary Engines

A Clerget 9B from 1917 is preserved at the Museum of Lincolnshire Life.
A Clerget 9B is also exhibited for public viewing at the Fleet Air Arm Museum, located at RNAS Yeovilton.

Rotary Engines in Operation

The Shuttleworth Collection at Old Warden Aerodrome, UK, maintains airworthy examples including a late-model Sopwith Triplane (G-BOCK) powered by an original 9B engine and a Sopwith Camel (G-BZSC) fitted with a long-stroke 9Bf. These aircraft regularly participate in summer airshows.

X16 Engine

Clerget 16X

An experimental four-row X engine configuration with 16 cylinders producing 420 hp (310 kW). This was the sole non-rotary engine developed by Clerget-Blin.

Diesel Radial Engines

Following Clerget-Blin’s insolvency in 1920, Pierre Clerget joined the Service Technique de l'Aéronautique (STAé), focusing on aircraft diesel engine development until his passing in 1943.

Clerget 9A: (1929) nine-cylinder, single-row radial delivering 100 hp (75 kW).
Clerget 9B
Clerget 9C: Produced under license by Hispano-Suiza as the Hispano-Suiza 9T.
Clerget 14F-01: (1937) fourteen-cylinder, two-row radial engine installed in a Potez 25 biplane.

Clerget 14F-02


Clerget 14Fcs

16H Engine

The last design by Clerget was the V-16 Type Transatlantique Clerget 16H, which generated 2,000 hp (1,500 kW) through the use of four Rateau turbochargers.

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