The Bristol Hercules is a 14-cylinder two-row radial

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 ...

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 wealthy ...

and produced by the

Bristol Engine 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 ...

starting in 1939. It was the most numerous of their single

sleeve valve The sleeve valve is a type of valve mechanism for piston engines, distinct from the usual poppet valve. Sleeve valve engines saw use in a number of pre-World War II luxury cars and in the United States in the Willys-Knight car and light truck. ...

( Burt-McCollum, or

Argyll Argyll (; archaically Argyle, in modern Gaelic, ), sometimes called Argyllshire, is a historic county and registration county of western Scotland. Argyll is of ancient origin, and corresponds to most of the part of the ancient kingdom of ...

, type) designs, powering many

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...

in the mid-

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

timeframe. The Hercules powered a number of aircraft types, including Bristol's own

Beaufighter The Bristol Type 156 Beaufighter (often called the Beau) is a British multi-role aircraft developed during the Second World War by the Bristol Aeroplane Company. It was originally conceived as a heavy fighter variant of the Bristol Beaufort ...

heavy fighter design, although it was more commonly used on

bomber A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching aerial torpedo, torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped ...

s. The Hercules also saw use in civilian designs, culminating in the 735 and 737 engines for such as the

Handley Page Hastings The Handley Page HP.67 Hastings is a retired British troop-carrier and freight transport aircraft designed and manufactured by aviation company Handley Page for the Royal Air Force (RAF). Upon its introduction to service during September 1948, ...

C1 and C3 and Bristol Freighter. The design was also licensed for production in

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

by SNECMA.

Design and development

Shortly after the end of World War I, the Shell company, Asiatic Petroleum, commissioned

Harry Ricardo Sir Harry Ralph Ricardo (26 January 1885 – 18 May 1974) was an English engineer who was one of the foremost engine designers and researchers in the early years of the development of the internal combustion engine. Among his many other works, ...

to investigate problems of fuel and engines. His book was published in 1923 as “The Internal Combustion Engine”. Ricardo postulated that the days of the poppet valve were numbered and that a sleeve valve alternative should be pursued. The rationale behind the single

design was two-fold: to provide optimum intake and exhaust gas flow in a two-row radial engine, improving its volumetric efficiency and to allow higher compression ratios, thus improving its thermal efficiency. The arrangement of the cylinders in two-row radials made it very difficult to utilise four valves per cylinder, consequently all non-sleeve valve two- and four-row radials were limited to the less efficient two-valve configuration. Also, as combustion chambers of sleeve-valve engines are uncluttered by valves, especially hot exhaust valves, so being comparatively smooth they allow engines to work with lower

octane number An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonatin ...

fuels using the same compression ratio. Conversely, the same octane number fuel may be utilised while employing a higher compression ratio, or supercharger pressure, thus attaining either higher economy or power output. The downside was the difficulty in maintaining sufficient cylinder and sleeve lubrication. Manufacturing was also a major problem. Sleeve valve engines, even the mono valve Fedden had elected to use, were extremely difficult to make. Fedden had experimented with sleeve valves in an inverted V-12 as early as 1927 but did not pursue that engine any further. Reverting to nine cylinder engines, Bristol had developed a sleeve valve engine that would actually work by 1934, introducing their first sleeve-valve designs in the 750

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 the ...

(560 kW) class

Perseus In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...

and the 500 hp (370 kW) class Aquila that they intended to supply throughout the 1930s. Aircraft development in the era was so rapid that both engines quickly ended up at the low-power end of the military market and, in order to deliver larger engines, Bristol developed 14-cylinder versions of both. The Perseus evolved into the Hercules, and the Aquila into the

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological characters named Taurus * ''Bos taurus ...

. These smooth-running engines were largely hand-built, which was incompatible with the needs of wartime production. At that time, the tolerances were simply not sufficiently accurate to ensure the mass production of reliable engines. Fedden drove his teams mercilessly, at both Bristol and its suppliers, and thousands of combinations of alloys and methods were tried before a process was discovered which used centrifugal casting to make the sleeves perfectly round. This final success arrived just before the start of the Second World War. In 1937 Bristol acquired a Northrop Model 8A-1, the export version of the

A-17 A17, A 17, A.17 or A-17 is a three-letter acronym that may refer to: * A17 Cutty Sark, a 1930 British Saro aircraft * A17 road, in several countries * Aero A.17, a 1922 Czech sailplane * ARM Cortex-A17, a microprocessor core * British NVC community ...

attack bomber, and modified it as a testbed for the first Hercules engines. The first Hercules engines were available in 1939 as the 1,290 hp (960 kW) Hercules I, soon improved to 1,375 hp (1,025 kW) in the Hercules II. The major version was the Hercules VI which delivered 1,650 hp (1,230 kW), and the late-war Hercules XVII produced 1,735 hp (1,294 kW). In 1939 Bristol developed a

modular Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a sy ...

engine installation for the Hercules, a so-called " power-egg", allowing the complete engine and cowling to be fitted to any suitable aircraft. A total of over 57,400 Hercules engines were built.

Applications

''Note'':List from Lumsden 2003, some of these aircraft were used for test purposes, the Hercules not necessarily being the main powerplant *

Armstrong Whitworth Albemarle The Armstrong Whitworth A.W.41 Albemarle was a twin-engine military transport aircraft, transport aircraft developed by the United Kingdom, British aircraft manufacturer Armstrong Whitworth and primarily produced by A.W. Hawksley Ltd, a subsid ...

* Avro Lancaster B.II * Avro York C.II *

Bristol Beaufighter The Bristol Type 156 Beaufighter (often called the Beau) is a British multi-role aircraft developed during the Second World War by the Bristol Aeroplane Company. It was originally conceived as a heavy fighter variant of the Bristol Beaufort ...

* Bristol Freighter * Bristol Superfreighter * Breguet 890 Mercure *

CASA C-207 Azor The CASA C-207 Azor was a transport aircraft produced by Construcciones Aeronáuticas SA (CASA). It was a scaled-up version of the CASA C-202 Halcón and was designed for the domestic civil market. The C-207 received no civil orders, but the Span ...

Fokker T.IX __NOTOC__ The Fokker T.IX was a Dutch twin-engined bomber designed and built by Fokker for the Royal Netherlands East Indies Army Air Force as a replacement for their obsolescent Martin-built bombers. Development Design of the T.IX was started in ...

Folland Fo.108 The Folland Fo.108, also known as the Folland 43/37 and by the nickname Folland Frightful (or Frightener), was a large monoplane engine testbed aircraft of the 1940s. Design and development The Fo.108 was Folland's response to Air Ministry Spe ...

Handley Page Halifax The Handley Page Halifax is a British Royal Air Force (RAF) four-engined heavy bomber of the Second World War. It was developed by Handley Page to the same specification as the contemporary twin-engine Avro Manchester. The Halifax has its or ...

* Handley Page Hermes * Nord Noratlas * Northrop 8A (One Swedish 8A-1 was bought by Bristol to test the engine) * Northrop Gamma 2L * Saro Lerwick *

Short S.26 The Short S.26 G-class was a large transport flying boat designed and produced by the British aircraft manufacturer Short Brothers. It was designed to achieve a non-stop transatlantic capability, increasing the viability of long distant service ...

Short Seaford The Short S.45 Seaford was a 1940s flying boat, designed as a long range maritime patrol bomber for RAF Coastal Command. It was developed from the Short S.25 Sunderland, and initially ordered as "Sunderland Mark IV". Background In 1942, the Air ...

Short Solent The Short Solent is a passenger flying boat that was produced by Short Brothers in the late 1940s. It was developed from the Short Seaford, itself a development of the Short Sunderland military flying boat design. The first Solent flew in 194 ...

Short Stirling The Short Stirling was a British four-engined heavy bomber of the Second World War. It has the distinction of being the first four-engined bomber to be introduced into service with the Royal Air Force (RAF). The Stirling was designed during t ...

Vickers Valetta The Vickers Valetta is a twin-engine military transport aircraft developed and produced by the British manufacturing company Vickers-Armstrongs Ltd. Developed from the Vickers VC.1 Viking compact civil airliner, it was an all-metal mid-wing m ...

* Vickers Varsity *

Vickers VC.1 Viking The Vickers VC.1 Viking is a British twin-engine short-range airliner derived from the Vickers Wellington bomber and built by Vickers-Armstrongs Limited at Brooklands near Weybridge in Surrey. After the Second World War, the Viking was an i ...

Vickers Wellesley The Vickers Wellesley was a medium bomber that was designed and produced by the British aircraft manufacturer Vickers-Armstrongs at Brooklands near Weybridge, Surrey. It was one of two aircraft to be named after Arthur Wellesley, 1st Duke of We ...

Vickers Wellington The Vickers Wellington was a British twin-engined, long-range medium bomber. It was designed during the mid-1930s at Brooklands in Weybridge, Surrey. Led by Vickers-Armstrongs' chief designer Rex Pierson; a key feature of the aircraft is its g ...

Specifications (Hercules II)

References

Notes

Bibliography

* *Gunston, Bill. (1993) ''The Development of Piston Aero Engines'', Haynes Publishing, Somerset *Gunston, Bill. (1995) ''Classic World War II Aircraft Cutaways.'' Osprey. *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, UK: Airlife Publishing, 2003. . *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

Running a Hercules for the first time in 30 years

Image of the gear system for the sleeve drive
a 1948 advert for the Hercules in ''Flight'' magazine

a 1948 ''Flight'' advertisement for the Hercules {{Bristol aeroengines

Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...

Aircraft air-cooled radial piston engines Sleeve valve engines 1930s aircraft piston engines