Hercules
Cutaway Bristol Hercules engine at the National Museum of Flight, East Fortune, Scotland
Type Piston aircraft engine
National origin United Kingdom
Manufacturer Bristol Aeroplane Company
First run January 1936
Major applications Bristol Beaufighter
Short Stirling
Handley Page Halifax
Number built 57,400
Developed from Bristol Perseus
Developed into Bristol Centaurus

The Bristol Hercules is a 14-cylinder two-row radial aircraft engine designed by Sir Roy Fedden and produced by the Bristol Engine Company starting in 1939. It was the most numerous of their single sleeve valve (Burt-McCollum, or Argyll, type) designs, powering many aircraft in the mid-World War II timeframe.

The Hercules powered a number of aircraft types, including Bristol's own Beaufighter heavy fighter design, although it was more commonly used on bombers. The Hercules also saw use in civilian designs, culminating in the 735 and 737 engines for such as the Handley Page Hastings C1 and C3 and Bristol Freighter. The design was also licensed for production in France by SNECMA.

Design and development

Shortly after the end of World War I, the Shell company, Asiatic Petroleum, commissioned Harry Ricardo to investigate problems of fuel and engines. His book was published in 1923 as “The Internal Combustion Engine”.[1] Ricardo postulated that the days of the poppet valve were numbered and that a sleeve valve alternative should be pursued.[2]

The rationale behind the single sleeve valve 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 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 (560 kilowatts) class Perseus 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.

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.[2]

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.[3]

In 1939 Bristol developed a modular engine installation for the Hercules, a so-called "power-egg", allowing the complete engine and cowling to be fitted to any suitable aircraft.[4]

A total of over 57,400 Hercules engines were built.

Variants and applications

Hercules fitted to a Vickers Varsity on display at the Newark Air Museum
Bristol Hercules in Aviation Museum Kbely, Prague
Bristol Hercules engine. Note the absence of pushrods on the cylinders. Each cylinder has two exhaust ports on the front (short L-shaped tubes) and three intake ports on the back supplied through a single manifold.
Bristol Hercules XVII engine

Hercules I (1936) – 1,150 hp (860 kW), single-speed supercharger, run on 87 octane fuel. Applications:[5]

Hercules II (1938) – 1,375 hp (1,025 kW), single-speed supercharger, run on 87 octane fuel. Applications:[5]

Hercules III (1939) – 1,400 hp (1,000 kW), two-speed supercharger, run on either 87 or 100 octane fuel. Applications:[6]

Hercules IV (1939) – 1,380 hp (1,030 kW), single-speed supercharger, run on 87 octane fuel. Applications:[6]

Hercules V (1939) – 1,380 hp (1,030 kW), civil prototype derived from the Hercules IV but not developed.[6]

Hercules VI (1941) – 1,615 hp (1,204 kW), two-speed supercharger, run on either 87 or 100 octane fuel. Applications:[6]

Hercules VII production cancelled.[6]

Hercules VIII – 1,650 hp (1,230 kW), very high-altitude version of the Hercules II, single-speed supercharger with an auxiliary high-altitude single-speed 'S' supercharger. Applications:[6]

Hercules X (1941) – 1,420 hp (1,060 kW), derived from the Hercules III. Applications:[7]

  • Armstrong Whitworth Albemarle Mks I, II, V & VI
  • Bristol Beaufighter Mk I
  • Short Stirling Mk I
  • Vickers Wellington Mk III

Hercules XI (1941) – 1,590 hp (1,190 kW), derived from the Hercules III, run on 100 octane fuel. Applications:[8]

  • Armstrong Whitworth Albemarle Mks I, II, V & VI
  • Bristol Beaufighter Mk I
  • Folland Fo.108
  • Short Stirling Mks I, II & III
  • Vickers Wellington Mks III & X

Hercules XII – derived from the Hercules IV.[8]

Hercules XIV (1942) – 1,500 hp (1,100 kW), developed for the civil market and used by BOAC, run on 100 octane fuel. Application:[8]

  • Short S.26

Hercules XVMT – 1,650 hp (1,230 kW), very high-altitude development of the Hercules II, single-speed supercharger with an auxiliary high-altitude turbo-supercharger. Applications:[8]

  • Folland Fo.108
  • Vickers Wellington Mk V

Hercules XVI (1942) – 1,615 hp (1,204 kW), two-speed supercharger, run on either 87 or 100 octane fuel. Applications:[8]

  • Avro Lancaster Mk II
  • Avro York Mk II
  • Bristol Beaufighter Mks VIC, VIF & TFX
  • Handley Page Halifax Mks III, VI, VII & IX
  • Short Stirling Mks III, IV & V
  • Vickers Wellington Mks IX, X, XI, XII, XIII, XIV, XVII & XVIII

Hercules XVII (1943) – 1,615 hp (1,204 kW), two-speed supercharger locked in 'M' gear. Applications:[8]

  • Bristol Beaufighter Mks TFX & XIC
  • Handley Page Halifax Mks III, VI, VII & IX
  • Vickers Wellington Mks X, XI, XII, XIII, XIV, XVII & XVIII

Hercules XVIII – low-level development of the Hercules VI with cropped 12 in (300 mm) supercharger impellers. Applications:[8]

  • Bristol Beaufighter Mks TFX, XIC & 21

Hercules XIX (1943) – 1,725 hp (1,286 kW), a development of the Hercules XVII, the two-speed supercharger had cropped 12 in (300 mm) impellers locked in 'M' gear. Application:[8]

Hercules XX – similar to the Hercules XIX. Application:[8]

Hercules 36 – a development engine derived from the Hercules VI and Hercules XVI, run on 100 octane fuel.[8]

Hercules 38 – a development engine derived from the Hercules 36.[8]

Hercules 100 (1944) – 1,675 hp (1,249 kW), 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-type reduction gearing. Applications:[9]

Hercules 101 – 1,675 hp (1,249 kW), developed from the Hercules 100. The Hercules 103 was the torquemeter version. Applications:[10]

Hercules 105 – 1,675 hp (1,249 kW), developed from the Hercules 101 with modified supercharger gears. Applications:[10]

  • Handley Page Hastings C1

Hercules 106 – 1,675 hp (1,249 kW), developed from the Hercules 101. The Hercules 107 was the torquemeter version. Applications:[10]

  • Handley Page Hastings C2
  • Handley Page Hermes II

Hercules 110 – developed from the Hercules 101.[10]

Hercules 120 – 1,715 hp (1,279 kW), high-altitude development of the Hercules 101. The Hercules 121 was the torquemeter version. Applications:[10]

Hercules 130 – 1,715 hp (1,279 kW), development of the Hercules 100. Applications:[10]

Engines on display

Specifications (Hercules II)

Data from Lumsden.[5]

General characteristics

  • Type: 14-cylinder, two-row, supercharged, air-cooled radial engine
  • Bore: 5.75 in (146 mm)
  • Stroke: 6.5 in (165 mm)
  • Displacement: 2,360 cu in (38.7 L)
  • Length: 53.15 in (1,350 mm)
  • Diameter: 55 in (1,400 mm)
  • Dry weight: 1,929 pounds (875 kg)

Components

Performance

See also

Related development

Comparable engines

Related lists

References

Notes

  1. ↑ Gunston (1993), p. 32.
  2. 1 2 Gunston (1993), p. 151.
  3. ↑ "Something Up Its Sleeve". www.flightglobal.com. Archived from the original on 22 January 2018.
  4. ↑ "1939 | 1- - 1270 | Flight Archive". www.flightglobal.com. Archived from the original on 2 March 2014.
  5. 1 2 3 Lumsden (1994), p. 119.
  6. 1 2 3 4 5 6 Lumsden (1994), p. 120.
  7. ↑ Lumsden (1994), pp. 120–121.
  8. 1 2 3 4 5 6 7 8 9 10 11 Lumsden (1994), p. 121.
  9. ↑ Lumsden (1994), pp. 121–122.
  10. 1 2 3 4 5 6 Lumsden (1994), p. 122.
  11. ↑ "Engines List". City of Norwich Aviation Museum. Retrieved 27 August 2023.

Bibliography

  • Bridgman, Leonard, ed. Jane's All The World's Aircraft 1945–1946. London: Samson Low, Marston & Company, Ltd 1946.
  • Gunston, Bill (1993). The Development of Piston Aero Engines. Sparkford, Somerset: Haynes Publishing Group P.L.C. ISBN 1-85260-385-2.
  • Gunston, Bill (1995). Classic World War II Aircraft Cutaways. Oxford: Osprey Publishing. ISBN 0-7607-1399-5.
  • Gunston, Bill (2006). World Encyclopedia of Aero Engines: From the Pioneers to the Present Day (5th ed.). Stroud: Sutton. ISBN 0-7509-4479-X.
  • Lumsden, Alec (1994). British Piston Engines and Their Aircraft. Shrewsbury: Airlife Publishing Ltd. ISBN 1-85310-294-6.
  • White, Graham (1995). 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: Society of Automotive Engineers. ISBN 1-56091-655-9.
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