The Bristol Hercules is a 14-cylinder two-row

radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance (geometry), a directional coordinate in a polar coordinate system * Radial set * A ...

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 ...

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 ...

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 ...

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 tru ...

( Burt-McCollum, or

Argyll Argyll (; archaically Argyle; , ), sometimes called Argyllshire, is a Shires of Scotland, historic county and registration county of western Scotland. The county ceased to be used for local government purposes in 1975 and most of the area ...

, type) designs, powering many

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

in the mid-

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

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 t ...

heavy fighter A heavy fighter is an historic category of fighter aircraft produced in the 1930s and 1940s, designed to carry heavier weapons or operate at longer ranges than light fighter aircraft. To achieve performance, most heavy fighters were twin-engine ...

design, although it was more commonly used on

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. 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 Bristol Type 170 Freighter is a British twin-engine aircraft designed and built by the Bristol Aeroplane Company as both a freighter and airliner. Its best known use was as an air ferry to carry cars and their passengers over relatively s ...

. The design was also licensed for production in

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

SNECMA Safran Aircraft Engines, previously Snecma (''Société nationale d'études et de construction de moteurs d'aviation'') or Snecma Moteurs, is a French aerospace engine manufacturer headquartered in Courcouronnes and a subsidiary of Safran. It d ...

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 Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through ...

flow in a two-row radial engine, improving its

volumetric efficiency Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the equivalent volume of the fresh air drawn into the cylinder during the intake stroke (if the gases were at the reference condition for density) to th ...

and to allow higher compression ratios, thus improving its

thermal efficiency In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For ...

. 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 causing engine knocking. The higher the octane number, the more compression the fuel can withstand be ...

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 class

Perseus In Greek mythology, Perseus (, ; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of the Perseid dynasty. He was, alongside Cadmus and Bellerophon, the greatest Greek hero and slayer of ...

and the class

Aquila Aquila may refer to: Arts, entertainment, and media * ''Aquila'', a series of books by S.P. Somtow * ''Aquila'', a 1997 book by Andrew Norriss * ''Aquila'' (children's magazine), a UK-based children's magazine * ''Aquila'' (journal), an orni ...

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 ** Vṛṣabha, in vedic astrology * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological ch ...

. 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 attack bomber, and modified it as a testbed for the first Hercules engines. In 1939 Bristol developed a

modular Module, modular and modularity may refer to the concept of modularity. They may also refer to: Computer science and engineering * Modular design, the engineering discipline of designing complex devices using separately designed sub-components ...

engine installation for the Hercules, a so-called "

power-egg A power-egg is a complete "unitized" Modular design, modular engine installation, consisting of engine and all ancillary equipment, which can be swapped between suitably designed equipment, with standardised quick-changing attachment points and ...

", allowing the complete engine and cowling to be fitted to any suitable aircraft. A total of over 57,400 Hercules engines were built.

Variants

Hercules I (1936) – , single-speed

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 ...

, run on 87

octane Octane is a hydrocarbon and also an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers ...

fuel. Hercules II (1938) – , single-speed supercharger, run on 87 octane fuel. Hercules III (1939) – , two-speed supercharger, run on either 87 or 100 octane fuel. Hercules IV (1939) – , single-speed supercharger, run on 87 octane fuel. Hercules V (1939) – , civil prototype derived from the Hercules IV but not developed. Hercules VI (1941) – , two-speed supercharger, run on either 87 or 100 octane fuel. Hercules VII production cancelled. Hercules VIII – , very high-altitude version of the Hercules II, single-speed supercharger with an auxiliary high-altitude single-speed 'S' supercharger. Hercules X (1941) – , derived from the Hercules III. Hercules XI (1941) – , derived from the Hercules III, run on 100 octane fuel. Hercules XII – derived from the Hercules IV. Hercules XIV (1942) – , developed for the civil market and used by

BOAC British Overseas Airways Corporation (BOAC) was the British state-owned national airline created in 1939 by the merger of Imperial Airways and British Airways Ltd. It continued operating overseas services throughout World War II. After the ...

, run on 100 octane fuel. Hercules XVMT – , very high-altitude development of the Hercules II, single-speed supercharger with an auxiliary high-altitude

turbo-supercharger 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 the ...

. Hercules XVI (1942) – , two-speed supercharger, run on either 87 or 100 octane fuel. Hercules XVII (1943) – , two-speed supercharger locked in 'M' gear. Hercules XVIII – low-level development of the Hercules VI with cropped supercharger

impeller An impeller, or impellor, is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. Strictly speaking, propellers are a sub-clas ...

s. Hercules XIX (1943) – , a development of the Hercules XVII, the two-speed supercharger had cropped impellers locked in 'M' gear. Hercules XX – similar to the Hercules XIX. Hercules 36 – a development engine derived from the Hercules VI and Hercules XVI, run on 100 octane fuel. The Hercules 38 was a further development of the Hercules 36. Hercules 100 (1944) – , the first in a new sub-series of Hercules engines designed primarily for the impending post-war civil market. The entire series was split, some versions had standard epicyclic reduction gearing and parallel versions had a new

torquemeter A dynamometer or "dyno" is a device for simultaneously measuring the torque and rotational speed (RPM) of an engine, motor or other rotating prime mover so that its instantaneous power may be calculated, and usually displayed by the dynamomet ...

-type reduction gearing. Hercules 101 – , developed from the Hercules 100. The Hercules 103 was the torquemeter version. The Hercules 110 was a further development of the Hercules 101. Hercules 105 – , developed from the Hercules 101 with modified supercharger gears. Hercules 106 – , developed from the Hercules 101. The Hercules 107 was the torquemeter version. Hercules 120 – , high-altitude development of the Hercules 101. The Hercules 121 was the torquemeter version. The Hercules 200 was further modified version of the Hercules 120. Hercules 130 – , development of the Hercules 100. The Hercules 134 was a development with modified mounting ring and exhaust pipes for a rear manifold. Hercules 216 – , development of the Hercules 106 with the Hercules 230 power section and single speed supercharger. Applications: Hercules 230 – , development of the Hercules 130 with the re-designed power section and modified mounting ring and exhaust pipes for a rear manifold. The Hercules 270 was a development. The Hercules 231 and Hercules 271 were the torquemeter versions. Hercules 232 – modified development of the Hercules 230 for improved performance. The Hercules 233 was the torquemeter version. Hercules 234 – modified development of the Hercules 232. The Hercules 235 was the torquemeter version. The Hercules 238 was a military version of the Hercules 734 which itself was based on the Hercules 234. Hercules 260 – modified development of the Hercules 230 to suit reversible propellers. The Hercules 261 was the torquemeter version. Hercules 264 – , a development of the Hercules 260. The Hercules 265 was the torquemeter version. Hercules 268 – a further development of the Hercules 260. The Hercules 269 was the torquemeter version. Hercules 630 – , a civil development of the Hercules 100. The Hercules 631 was the torquemeter version. Hercules 632 – , a civil-series engine developed from the Hercules 630. The Hercules 633 was the torquemeter version. The Hercules 638 and Hercules 672, along with their torquemeter versions the Hercules 639 and Hercules 673 were developments of the Hercules 632. Hercules 634 – , a civil-series engine developed from the Hercules 630 with modified mounting ring and exhaust pipes for a rear manifold. The Hercules 635 was the torquemeter version. Hercules 636 – a civil-series engine developed from the Hercules 630 with modified mounting ring and exhaust pipes for a rear manifold. The Hercules 637 was the torquemeter version. The Hercules 637-2 and Hercules 637-3 were further torquemeter developments. Hercules 730 – , a civil-series engine developed from the Hercules 230 and 630 with improved power section, the Hercules 731 was the torquemeter version. Hercules 732 – a civil-series engine developed from the Hercules 730 with modified mounting ring and exhaust pipes for a rear manifold. The Hercules 733 was the torquemeter version. Hercules 734 – , a civil-series engine developed from the Hercules 730. The Hercules 735 was the torquemeter version. The Hercules 238 was a military version of the civil Hercules 734. Hercules 736 – , a civil-series engine developed from the Hercules 730. The Hercules 737 was the torquemeter version. Hercules 738 – a civil-series engine developed from the Hercules 730. Hercules 739 – the torquemeter version of the Hercules 738. Hercules 750 – a civil-series engine developed from the Hercules 730 to suit braking propellers. The Hercules 751 was the torquemeter version. Hercules 758 – , a civil-series development of the Hercules 750, the Hercules 759 was the torquemeter version. The Hercules 790 and its torquemeter version the Hercules 790 were further developed from the Hercules 758. Hercules 760 – a civil-series engine developed from the Hercules 730. Hercules 762 – , a civil-series high-altitude development of the Hercules 730 with modified supercharger. The Hercules 763 was the torquemeter version. Hercules 772 – , a civil-series development of the Hercules 762. The Hercules 773 was the torquemeter version.

Applications

Bristol Hercules uses: *

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

Avro Lancaster The Avro Lancaster, commonly known as the Lancaster Bomber, is a British World War II, Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to ...

Mk II *

Avro Tudor The Avro Type 688 Tudor was a British piston-engined airliner based on Avro's four-engine Avro Lincoln, Lincoln bomber, itself a descendant of the famous Avro Lancaster, Lancaster heavy bomber, and was Britain's first pressurised airliner. Cus ...

VII *

Avro York The Avro York was a British transport aircraft developed by Avro during the World War II, Second World War. The design was derived from the Avro Lancaster heavy bomber, several sections of the York and Lancaster being identical. Due to the impo ...

Mk II * Bréguet 890H Mercure prototype *

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 Beaufor ...

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 * Folland Fo.108 * GAL Universal Freighter *

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 Halton 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 ori ...

Handley Page Hermes The Handley Page HP.81 Hermes was a civilian airliner designed and produced by the United Kingdom, British aircraft manufacturer Handley Page. The Hermes was developed during the 1940s in parallel with the closely related Handley Page Hastings ...

Nord Noratlas The Nord Noratlas is a dedicated military transport aircraft, developed and manufactured by French aircraft manufacturer Nord Aviation. Development commenced during the late 1940s with the aim of producing a suitable aircraft to replace the num ...

Nord Noroit The Nord 1400 Noroit was a French reconnaissance and air-sea rescue flying boat designed and built by Nord Aviation for the French Navy. Development The Noroit was an amphibian flying boat designed for the French Navy, a cantilever gullwing mono ...

* Northrop Gamma 2L * Saro A.36 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 servic ...

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 Ai ...

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 19 ...

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) during the war (the earlier Handley ...

* SNCASE SE-1010 *

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 ...

Vickers Varsity The Vickers Varsity is a retired British twin-engined crew trainer operated by the Royal Air Force from 1951 to 1976. Design and development The Varsity was developed by Vickers and based on the Viking and Valetta to meet Air Ministry Spec ...

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, Vickers-Armstrongs Limited at Brooklands near Weybridge in Surrey. After the Second World War, ...

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 W ...

Vickers Wellington The Vickers Wellington (nicknamed the Wimpy) is 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 t ...

Engines on display

* RAF Snaith Museum https://www.facebook.com/RAFSnaith/ * A Bristol Hercules is on public display at the

City of Norwich Aviation Museum The City of Norwich Aviation Museum is a volunteer-run museum and charitable trust dedicated to the preservation of the aviation history of the county of Norfolk, England. The museum is located on the northern edge of Norwich International ...

in Horsham St Faith, Norfolk. * Two incomplete and badly corroded examples from aircraft lost in the vicinity of Texel and recovered from the sea are on display at the

Museum Kaapskil A museum is an institution dedicated to displaying or preserving culturally or scientifically significant objects. Many museums have exhibitions of these objects on public display, and some have private collections that are used by researchers ...

in Oudeschild, Texel, NL.

Specifications (Hercules II)

References

Notes

Bibliography

* * * * * *

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