The Bristol Mercury is a British nine-cylinder, air-cooled, single-row, piston radial engine. Designed by Roy Fedden of the

Bristol Aeroplane Company The Bristol Aeroplane Company, originally the British and Colonial Aeroplane Company, was both one of the first and one of the most important British aviation companies, designing and manufacturing both airframes and aircraft engines. Notable a ...

it was used to power both civil and military aircraft of the 1930s and 1940s. Developed from the earlier Jupiter engine, later variants could produce 800 horsepower (600 kW) from its capacity of 1,500 cubic inches (25 L) by use of a geared

supercharger In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement. The current categorisation is that a supercharger is a form of forced induct ...

. Almost 21,000 engines were produced, with a number also being built under license elsewhere in Europe. Several examples remain airworthy, with other preserved examples on public display in

aviation museum An aviation museum, air museum, or air and space museum is a museum exhibiting the history and cultural artifacts, artifacts of aviation. In addition to actual, replica or accurate reproduction aircraft, exhibits can include photographs, maps, P ...

Design and development

The Mercury was developed by the

in 1925 as their

Bristol Jupiter The Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turn ...

was reaching the end of its lifespan. Although the Mercury initially failed to attract much interest, the Air Ministry eventually funded three prototypes and it became another winner for the designer Roy Fedden. With the widespread introduction of

s to the aviation industry in order to improve altitude performance, Fedden felt it was reasonable to use a small amount of boost at all times in order to improve performance of an otherwise smaller engine. Instead of designing an entirely new block, the existing Jupiter parts were re-used with the stroke reduced by one inch (25 mm). The smaller capacity engine was then boosted back to Jupiter power levels, while running at higher rpm and thus requiring a reduction gear for the

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

. The same techniques were applied to the original Jupiter-sized engine to produce the

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

. The Mercury's smaller size was aimed at fighter use and it powered the Gloster Gauntlet and its successor, the Gloster Gladiator. It was intended that the larger Pegasus would be for bombers, but as the power ratings of both engines rose, the Mercury was used in almost all roles. Perhaps its most famous use was in a twin-engine

light bomber A light bomber is a relatively small and fast type of military bomber aircraft that was primarily employed before the 1950s. Such aircraft would typically not carry more than one ton of ordnance. The earliest light bombers were intended to dro ...

, the Bristol Blenheim. In 1938 Roy Fedden pressed the Air Ministry to import supplies of 100 octane aviation spirit (gasoline) from the USA. This new fuel would allow aero engines to run at higher

compression ratio The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...

s and

boost pressure than the existing 87-octane fuel, thus increasing the power. The Mercury XV was one of the first British aero engines to be type-tested and cleared to use the 100-octane fuel in 1939. This engine was capable of running with a boost pressure of +9 lbs/sq.in (0.62 bar) and was first used in the Blenheim Mk IV. The Mercury was also the first British aero engine to be approved for use with variable-pitch propellers. The Bristol company and its shadow factories produced 20,700 examples of the engine. Outside the United Kingdom, Mercury was licence-built in Poland and used in their PZL P.11 fighters. It was also built by NOHAB in Sweden and used in the Swedish Gloster Gladiator fighters and in the Saab 17 dive-bomber. In Italy, it was built by Alfa Romeo as the Mercurius. In Czechoslovakia it was built by

Walter Engines Walter Aircraft Engines is an aircraft engine manufacturer and former automotive manufacturer. Its notable products include the Walter M601, M601 turboprop. The company is based in Prague, Czech Republic. It has been a subsidiary of GE Aviation ...

. In Finland, it was built by

Tampella Oy Tampella Ab was a Finnish heavy industry manufacturer, a maker of paper machines, locomotives, military weaponry, as well as wood-based products such as packaging. The company was based mainly in the Naistenlahti district of the city of ...

and mainly used on Bristol Blenheim bombers.

Variants

''Note:'' ;Mercury I :(1926) , direct drive. Schneider Trophy racing engine ;Mercury II :(1928) ,

5.3:1 ;Mercury IIA :(1928) ;Mercury III :(1929) , compression ratio 4.8:1, 0.5:1 reduction gear Bristol (NOHAB) Mercury

;Mercury IIIA :Minor modification of Mercury III ;Mercury IV :(1929) , 0.656:1 reduction gear ;Mercury IVA :(1931) ;Mercury IVS.2 :(1932) ;Mercury (Short stroke) :Unsuccessful experimental short stroke (5.0 in) version, ;Mercury V : (became the Pegasus IS.2) ;Mercury VIS :(1933) Bristol Mercury

;Mercury VISP :(1931) , 'P' for Persia. ;Mercury VIS.2 :(1933) ;Mercury VIA :(1928) (became the Pegasus IU.2) ;Mercury VIIA : (became the Pegasus IM.2) ;Mercury VIII :(1935) , compression ratio 6.25:1, lightened engine. ;Mercury VIIIA :Mercury VIII fitted with gun synchronisation gear for the Gloster Gladiator MkII ;Mercury VIIIA :535 hp, second use of VIIIA designation, (became the Pegasus IU.2P) ;Mercury IX :(1935) , lightened engine. ;Mercury X :(1937) ;Mercury XI :(1937) ;Mercury XII (1937) ;Mercury XV :(1938) , developed from Mercury VIII. Converted to run on 100 Octane fuel (previously 87 Octane). ;Mercury XVI : ;Mercury XX :(1940) ;Mercury 25 :(1941) , Mercury XV with crankshaft modifications. ;Mercury 26 :, Mercury 25 with modified carburettor. ;Mercury 30 :(1941) , Mercury XX with crankshaft modifications. ;Mercury 31 :(1945) , Mercury 30 with carburettor modifications and fixed pitch propeller for Hamilcar X.

Applications

''Note:'' *

Airspeed Cambridge The Airspeed AS.45 Cambridge was a British advanced trainer of the Second World War built by Airspeed Limited. It did not reach the production stage. Development The AS.45 was designed in response to Air Ministry Specification T.4/39 for a ...

* Blackburn Skua * Boulton Paul P.108 * Bristol Blenheim *

Bristol Bolingbroke The Bristol Fairchild Bolingbroke is a maritime patrol aircraft and trainer used by the Royal Canadian Air Force during the Second World War. Built by Fairchild-Canada, it was a license-built version of the Bristol Blenheim Mk IV bomber. De ...

* Bristol Bulldog * Bristol Bullpup * Bristol Type 101 * Bristol Type 118 *

Bristol Type 133 The Bristol Type 133 was a single-seat, single-engine monoplane fighter armed with four guns, using stressed-skin construction and with a retractable undercarriage. It was built by The Bristol Aeroplane Co. to meet Specification F.7/30. The ...

Bristol Type 142 The Bristol Blenheim is a British light bomber aircraft designed and built by the Bristol Aeroplane Company (Bristol) which was used extensively in the first two years of the Second World War, with examples still being used as trainers until t ...

* Bristol Type 146 * Bristol Type 148 *

Breda Ba.27 The Breda Ba.27 was a fighter produced in Italy in the 1930s, used by the Chinese Nationalist Air Force in the Second Sino-Japanese War. Design and development The Ba.27 was a low-wing braced monoplane with fixed tailwheel undercarriage. As or ...

Fairey Flycatcher The Fairey Flycatcher was a British single-seat biplane carrier-borne fighter aircraft made by Fairey Aviation Company which served from 1923 to 1934. It was produced with a conventional undercarriage for carrier use, although this could be exc ...

* Fokker D XXI *

Fokker G.1 The Fokker G.I was a Dutch twin-engined heavy fighter aircraft comparable in size and role to the German Messerschmitt Bf 110. Although in production prior to World War II, its combat introduction came at a time the Netherlands were overrun by t ...

* General Aircraft Hamilcar X *

Gloster Gamecock The Gloster Gamecock was a biplane fighter designed and produced by the British aircraft manufacturer Gloster. The Gamecock was a development of the earlier Grebe Mk III, an early interwar fighter procured by the Royal Air Force (RAF). Wor ...

* Gloster Gladiator * Gloster Gauntlet *

Gloster Gnatsnapper The Gloster SS.35 Gnatsnapper was a British naval biplane fighter design of the late 1920s. Two prototypes were built but the type did not enter production. Design and development The Gnatsnapper was a submission to Air Ministry specification ...

* Gloster Goring * Hawker Audax * Hawker F.20/27 * Hawker Fury * Hawker Hart * Hawker Hind * Hawker Hoopoe * Hawker F.20/27 *

IMAM Ro.30 The IMAM Ro.30 was a 1930s Italy, Italian observation biplane designed and built by Industrie Meccaniche e Aeronautiche Meridionali. It was only built in limited numbers before being replaced by the IMAM Ro.37, Ro.37. Development Following the ...

Koolhoven F.K.52 Koolhoven F.K.52 was a Dutch-designed, two-seat reconnaissance-fighter biplane, which was developed in the 1930s by Koolhoven. The aircraft was equipped with an enclosed cockpit and single-strut landing gear. Only six aircraft were produced. The ...

* Letov Š-31 * Miles Martinet * Miles Master * PZL P.11 * Saab 17 *

Short Crusader The Short Crusader also called the Short-Bristow Crusader and Short-Bristol Crusader was a British racing seaplane of the 1920s, built by Short Brothers to compete in the 1927 Schneider Trophy race. Background Although inline engines had a cle ...

* Supermarine Sea Otter * Valmet Vihuri *

Vickers Jockey The Vickers Type 151 Jockey was an experimental low-wing monoplane interceptor fighter powered by a radial engine. It was later modified into the Type 171 Jockey II, which had a more powerful engine and detail improvements. Only one was built; ...

Westland Interceptor The Westland Interceptor was a fighter developed by the British company Westland Aircraft to Air Ministry Specification ''F.20/27''. When tested in 1929 and 1930, it showed unsatisfactory handling characteristics and was rejected by the RAF in ...

* Westland Lysander

Airworthy examples

The Shuttleworth Collection operates two Bristol Mercury powered aircraft: A Westland Lysander III (''G-AZWT'') and a

Gloster Gladiator I The Gloster Gladiator is a British biplane fighter. It was used by the Royal Air Force (RAF) and the Fleet Air Arm (FAA) (as the Sea Gladiator variant) and was exported to a number of other air forces during the late 1930s. Developed priva ...

(''G-AMRK'') which can be seen during flying displays at Old Warden Aerodrome, Bedfordshire. The Aircraft Restoration Company based at Duxford Airfield also operate a Mercury powered Westland Lysander (''G-CCOM'') as well as a

Bristol Blenheim I The Bristol Blenheim is a British light bomber aircraft designed and built by the Bristol Aeroplane Company (Bristol) which was used extensively in the first two years of the Second World War, with examples still being used as trainers until t ...

(''G-BPIV'') light bomber fitted with two Bristol Mercurys, which can be seen at air displays at

IWM Duxford Imperial War Museum Duxford is a branch of the Imperial War Museum near Duxford in Cambridgeshire, England. Britain's largest aviation museum, Duxford houses the museum's large exhibits, including nearly 200 aircraft, military vehicles, artill ...

as well as across the UK. The Fighter Collection, also currently based at Duxford Airfield, operate a 1939 Gloster Gladiator II (''G-GLAD'') powered by a Bristol Mercury XX. The

Canadian Warplane Heritage Museum The Canadian Warplane Heritage Museum is an aviation museum located at the John C. Munro Hamilton International Airport in Mount Hope, Ontario, Canada. The museum has 47 military jets and propeller-driven aircraft on display. Displayed is a co ...

has a Lysander IIIA in flying condition as does the

Vintage Wings of Canada Vintage Wings of Canada is a not for profit, charitable organization, with a collection of historically significant aircraft. The facility is located at the Gatineau-Ottawa Executive Airport, Quebec, Canada. It was founded by former Cognos CE ...

Engines on display

*A Bristol Mercury VII is on display at the Royal Air Force Museum London.RAF Museum - Bristol Mercury
Retrieved: 4 August 2009 *Another example of a Bristol Mercury VII is on display at 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 ...

. *A sectioned Bristol Mercury is on 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.

Specifications (Mercury VI-S)

References

Notes

Bibliography

* Bridgman, L, (ed.) (1998) ''Jane's Fighting Aircraft of World War II.'' Crescent. *Gunston, Bill. ''World Encyclopedia of Aero Engines: From the Pioneers to the Present Day''. 5th edition, Stroud, UK: Sutton, 2006. * Lumsden, Alec. ''British Piston Engines and Their Aircraft''. Marlborough, Wiltshire: Airlife Publishing, 2003. . * Warner, G. ''The Bristol Blenheim: A Complete History''. London: Crécy Publishing, 2nd edition 2005. . *White, Graham. ''Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II''. Warrendale, Pennsylvania: SAE International, 1995.

External links

Recorded sound of the Mercury V S2 engine
used in

PZL P.11c The PZL P.11 was a Polish fighter aircraft, designed and constructed during the early 1930s by Warsaw-based aircraft manufacturer PZL. Possessing an all-metal structure, metal-covering, and high-mounted gull wing, the type held the distinction of ...

( MP3 format) {{Walter aeroengines Aircraft air-cooled radial piston engines

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

1920s aircraft piston engines