The Bristol Mercury is a British nine-cylinder, air-cooled, single-row, piston

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. ...

. Designed by

Roy Fedden Sir Alfred Hubert Roy Fedden MBE, FRAeS (6 June 1885 – 21 November 1973) was an engineer who designed most of Bristol Engine Company's successful piston aircraft engine designs. Early life Fedden was born in the Bristol area to fairly weal ...

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 ...

it was used to power both civil and military aircraft of the 1930s and 1940s. Developed from the earlier

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

engine, later variants could produce 800

horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

(600 kW) from its capacity of 1,500

cubic inch The cubic inch (symbol in3) is a unit of volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its three dimensions (length, width, and height) being one inch long which is equivalent ...

es (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 (engine), displacement. It is a form of forced induction that is mechanically ...

. 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, Ph ...

Design and development

The Mercury was developed by the

in 1925 as their

Bristol Jupiter The Bristol Jupiter is a British nine-cylinder single-row piston radial engine that was 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 developme ...

was reaching the end of its lifespan. Although the Mercury initially failed to attract much interest, the

Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force and civil aviation that existed from 1918 to 1964. It was under the political authority of the ...

eventually funded three prototypes and it became another winner for the designer

. 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 (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 a working flu ...

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

Pegasus Pegasus (; ) is a winged horse in Greek mythology, usually depicted as a white stallion. He was sired by Poseidon, in his role as horse-god, and foaled by the Gorgon Medusa. Pegasus was the brother of Chrysaor, both born from Medusa's blood w ...

. The Mercury's smaller size was aimed at fighter use and it powered the

Gloster Gauntlet The Gloster Gauntlet was a single-seat biplane fighter designed and produced by the British aeroplane manufacturer Gloster Aircraft in the 1930s. It was the last fighter to be operated by the Royal Air Force (RAF) to have an open cockpit, and ...

and its successor, the

Gloster Gladiator 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 privat ...

. It was intended that the larger Pegasus would be for

bomber A bomber is a military combat aircraft that utilizes air-to-ground weaponry to drop bombs, launch aerial torpedo, torpedoes, or deploy air-launched cruise missiles. There are two major classifications of bomber: strategic and tactical. Strateg ...

s, 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 dr ...

, the

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

. In 1938 Roy Fedden pressed the Air Ministry to import supplies of 100 octane aviation spirit from the US. This new fuel would allow aero engines to run at higher

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

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 by

Państwowe Zakłady Lotnicze PZL (''Państwowe Zakłady Lotnicze'' - State Aviation Works) was the largest Poland, Polish aerospace manufacturer of the interwar period, and a brand of their aircraft. Based in Warsaw between 1928 and 1939, PZL introduced a variety of well-reg ...

in Poland and used in the PZL P.11 fighters. It was also built by

NOHAB NOHAB (Nydqvist & Holm AB) was a manufacturing company based in the city of Trollhättan, Sweden. History The company was founded by Antenor Nydqvist, Johan Magnus Lidström and Carl Olof Holm in 1847 as ''Trollhättans Mekaniska Verkstad'' as ...

in Sweden and used in the Swedish Gloster Gladiator fighters and in the

Saab 17 The Saab 17 is a Sweden, Swedish single-engine monoplane reconnaissance dive-bomber aircraft of the 1940s originally developed by AB Svenska Järnvägsverkstädernas Aeroplanavdelning, ASJA prior to its merger into Saab AB , Saab. It was the fir ...

dive-bomber. In Italy, it was built by

Alfa Romeo Alfa Romeo Automobiles S.p.A. () is an Italian carmaker known for its sports-oriented vehicles, strong auto racing heritage, and iconic design. Headquartered in Turin, Italy, it is a subsidiary of Stellantis Europe and one of 14 brands of mu ...

as the Mercurius. In

Czechoslovakia Czechoslovakia ( ; Czech language, Czech and , ''Česko-Slovensko'') was a landlocked country in Central Europe, created in 1918, when it declared its independence from Austria-Hungary. In 1938, after the Munich Agreement, the Sudetenland beca ...

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 Aerospac ...

. In Finland, it was built by

Tampella Oy Tampella Ab was a Finland, 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, Naistenlahti di ...

and mainly used on

bombers.

Variants

''Note:'' ;Mercury I :(1926) , direct drive.

Schneider Trophy The Coupe d'Aviation Maritime Jacques Schneider, also known as the Schneider Trophy, Schneider Prize or (incorrectly) the Schneider Cup is a trophy that was awarded first annually, and later biennially, to the winner of a race for seaplanes and ...

racing engine ;Mercury II :(1928) ,

5.3:1 ;Mercury IIA :(1928) ;Mercury III :(1929) , compression ratio 4.8:1, 0.5:1 reduction gear ;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 Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

. ;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 * Blackburn Skua * Boulton Paul P.108 *

* Bristol Bolingbroke *

Bristol Bulldog The Bristol Bulldog is a British Royal Air Force single-seat biplane Fighter aircraft, fighter designed during the 1920s by the Bristol Aeroplane Company. More than 400 Bulldogs were produced for the RAF and overseas customers, and it was one ...

* Bristol Bullpup * Bristol Type 101 * Bristol Type 118 * Bristol Type 133 * Bristol Type 142 * Bristol Type 146 * Bristol Type 148 * Breda Ba.27 * Caproni Ca.114 * Fairey Flycatcher * Fokker D XXI * Fokker G.1 * General Aircraft Hamilcar X * Gloster Gamecock *

* Gloster Gnatsnapper * Gloster Goring * Hawker Audax * Hawker F.20/27 *

Hawker Fury The Hawker Fury is a British biplane fighter aircraft used by the Royal Air Force in the 1930s. It was a fast, agile aircraft, and the first interceptor in RAF service faster than in level flight. It was the fighter counterpart to the Hawke ...

Hawker Hart The Hawker Hart is a British two-seater biplane light bomber aircraft that saw service with the Royal Air Force (RAF). It was designed during the 1920s by Sydney Camm and manufactured by Hawker Aircraft. The Hart was a prominent British aircraf ...

Hawker Hind The Hawker Hind is a British light bomber of the inter-war years produced by Hawker Aircraft for the Royal Air Force. It was developed from the Hawker Hart day bomber introduced in 1931 in aviation, 1931. Design and development An improved Ha ...

* Hawker Hoopoe * Hawker F.20/27 * IMAM Ro.30 * Koolhoven F.K.52 * Letov Š-31 * Miles Martinet *

Miles Master The Miles M.9 Master was a British two-seat monoplane advanced trainer designed and built by aviation company Miles Aircraft, Miles Aircraft Ltd. It was inducted in large numbers into both the Royal Air Force (RAF) and Fleet Air Arm (FAA) durin ...

* PZL P.11 * PZL.50 *

* Short Crusader *

Supermarine Sea Otter The Supermarine Sea Otter was an amphibious aircraft designed and built by the British aircraft manufacturer Supermarine. It was the final biplane flying boat to be designed by the company, and the last biplane to enter service with both the R ...

Valmet Vihuri Valmet Vihuri (Finnish language, Finnish for ''Gale'') was a Finland, Finnish advanced two-seat fighter trainer aircraft, serving in the Finnish Air Force between 1953 and 1959. Only a few airframes have survived, including one at the Central Fin ...

* Vickers Jockey * Westland Interceptor *

Westland Lysander The Westland Lysander is a British Army cooperation aircraft, army co-operation and liaison aircraft produced by Westland Aircraft that was used immediately before and during the Second World War. After becoming obsolete in the army co-operat ...

Airworthy examples

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 ...

operates two Bristol Mercury powered aircraft: A Westland Lysander III (''G-AZWT'') and a Gloster Gladiator I (''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 designed and built by the Bristol Aeroplane Company, which was used extensively in the first two years of the Second World War, with examples still being used as trainers until the end of the war. ...

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

Engines on display

*A Bristol Mercury VII is on display at the

Royal Air Force Museum London The Royal Air Force Museum London (also commonly known as the RAF Museum) is located on the former Hendon Aerodrome, in North London's Borough of Barnet. It includes five buildings and hangars showing the history of aviation and the Royal Air ...

.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 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 ...

. *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 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 ...

. *Bristol Mercury V is in running condition mounted on last PZL P.11 fighter at the Muzeum Lotnictwa Polskiego in

Kraków , officially the Royal Capital City of Kraków, is the List of cities and towns in Poland, second-largest and one of the oldest cities in Poland. Situated on the Vistula River in Lesser Poland Voivodeship, the city has a population of 804,237 ...

. * A Tampella Mercury is displayed next to

Finnish Air Force Museum The Finnish Air Force Museum (), formerly the Aviation Museum of Central Finland (), is an aviation museum located near Jyväskylä Airport in Tikkakoski, Jyväskylä, Finland. The museum exhibits the aviation history of Finland, from the early ...

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 (

MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany under the lead of Karlheinz Brandenburg. It was designed to greatly reduce the amount ...

format) {{Walter aeroengines Aircraft air-cooled radial piston engines Mercury 1920s aircraft piston engines