The Rolls-Royce Kestrel (internal type F) is a 21.25 litre (1,295 in³) V-12

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 ...

from

Rolls-Royce Rolls-Royce (always hyphenated) may refer to: * Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct Automobiles * Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...

. It was their first cast-block engine, and used as the pattern for most of their future piston-engine designs. Used during the

interwar period In the history of the 20th century, the interwar period, also known as the interbellum (), lasted from 11 November 1918 to 1 September 1939 (20 years, 9 months, 21 days) – from the end of World War I (WWI) to the beginning of World War II ( ...

, it was fitted to a number of British fighters and

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

of the era, including the

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 ...

and

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 ...

family, and the

Handley Page Heyford The Handley Page Heyford was a twin-engine biplane bomber designed and produced by the British aircraft manufacturer Handley Page. It holds the distinction of being the last biplane heavy bomber to be operated by the Royal Air Force (RAF). The ...

. The Kestrel engine was also sold to international air force customers; in this role it was used to power prototypes of the German

Messerschmitt Bf 109 The Messerschmitt Bf 109 is a monoplane fighter aircraft that was designed and initially produced by the Nazi Germany, German aircraft manufacturer Messerschmitt#History, Bayerische Flugzeugwerke (BFW). Together with the Focke-Wulf Fw 190, the ...

and the Junkers Ju 87 "Stuka" dive-bomber, as the

Junkers Jumo 210 The Jumo 210 was Junkers' first production inverted V12 gasoline aircraft engine, first produced in the early 1930s. Depending on the version it produced between 610 and 730 PS and can be considered a counterpart of the Rolls-Royce Kestrel in m ...

engines were not ready to be fitted. Several examples of the Kestrel engine remain airworthy today.

Design and development

Origin

Earlier in-line engine designs were generally built on top of a cast aluminum crankcase, with the cylinders, individually-machined steel cylinders, bolted on top. Given the forces involved, the system connecting the cylinders to the crankcase had to be robust, adding weight, and as a whole the engine was reliant on the structure of the crankcase to hold it together. In 1923, the Curtiss CR won the 1923

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 ...

. The CR was powered by the recently introduced

Curtiss D-12 The Curtiss D-12, sometimes identified with the military designation Curtiss V-1150, was an aircraft engine of 18.8 liter displacement. It was a water-cooled V12, producing 443 hp (330 kW) and weighing 693 lb (314 kg). It wa ...

engine, which replaced the individual cylinders with a cast aluminum block. This gave the engine much greater strength, allowing the rest of the engine to be greatly simplified, making it much lighter overall, as well as easier to assemble as the two parts simply bolted together in a single operation. It was also easy to convert existing assembly lines to the new system as the cast blocks were already being produced for the crankcase, and all that was required was new machines to mill the blocks to the accuracy needed for the pistons. The

was one of the most powerful engines of its era, and continued to exchange records with other contemporary high-power engines such as the

Napier Lion The Napier Lion is a 12-cylinder, petrol-fueled 'broad arrow' W12 engine, W12 configuration aircraft engine built by D. Napier & Son from 1917 until the 1930s. A number of advanced features made it the most powerful engine of its day and kept ...

. At the time, none of the British aero engine manufacturers could offer an engine which offered a similar power rating which was also as light and compact as the D-12. The D-12 was licensed by Fairey and introduced to the UK as the Felix. Arthur Rowledge, Chief Designer at Napier and the designer of the

engine, joined Rolls-Royce in 1921 to take up the role as "Chief Assistant to Mr F. H. Royce". Rowledge built a team to introduce a new engine using the cast block, but set the goal to surpass the D-12. This would be accomplished using

supercharging 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. It is a form of forced induction that is mechanically powered (usually by a b ...

at all altitudes, allowing it to outperform

naturally aspirated A naturally aspirated engine, also known as a normally aspirated engine, and abbreviated to N/A or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turboc ...

engines. Previously, supercharging (and turbocharging) was primarily used for high-altitude designs to offset the loss of ambient air pressure as the aircraft climbed, and thereby maintain power. But with the new construction technique, the engine would be so strong that it could be supercharged at all altitudes without overstressing the cylinders, allowing a smaller engine to operate as if it was larger, and thus improving its

power-to-weight ratio Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement ...

. The prototype Kestrel engine was first run in 1926, and one first flew in 1927, with a power rating of 450hp (335kW). The engine was normally aspirated in its initial form.

Improvements

The engine was first produced in 1927 at 450 hp (335 kW), which was soon improved in the I-B version to 525 hp (390 kW) by increasing the compression ratio to 7:1. The I-B variant saw widespread use in the

family of aircraft, a mainstay of British air power during the early 1930s. Development continued and the V model introduced the centrifugal supercharger, increasing power to 695hp (520kW). Increased availability of higher

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 ...

aviation fuel Aviation fuels are either petroleum-based or blends of petroleum and synthetic fuels, used to power aircraft. They have more stringent requirements than fuels used for ground applications, such as heating and road transport, and they contain add ...

s in the late 1930s allowed the engine to be boosted to higher power levels without suffering from

detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...

. The mark-XVI engine used in the

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 ...

M.9 prototype delivered 745hp (500kW), and the XXX variant of 1940 saw service at 720hp (537kW).

Cooling system

One key advance in the Kestrel was the use of a pressurised cooling system. Water boils at 100°C at

standard atmospheric pressure The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a ''reference pressure'' or ''standard pressure''. It is approximately equal to Earth's average atmospheric pressure at sea level. History The ...

, but this pressure decreases as altitude increases, and therefore the boiling point of water decreases with

altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...

. The amount of heat rejected by an air-to-air cooling system is a function of the maximum coolant temperature and volume, so the resulting decrease in cooling capacity became a limiting factor for aero engine power in this period, as the coolant has to be kept below boiling point. The solution was to pressurise the engine's entire cooling system, thereby raising the temperature at which the coolant would boil: not only does this help mitigate the decrease in cooling performance with altitude, but allows a smaller cooling system to be used in the aircraft for the same heat load. The Kestrel was built to maintain coolant pressure to keep the boiling point at about 150°C.

Variants

In early Kestrel variants, unsupercharged engines were available in two compression ratios, 'A' engines had a compression ratio of 6:1, and 'B' engines a high compression ratio of 7:1. The Kestrel was designed to be fitted with a gear-driven

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 ...

, in early Kestrel variants 'MS' engines were moderately supercharged and 'S' engines were fully supercharged. A number of Kestrel variants were produced by rebuilding or modifying earlier Marks. * Kestrel I, F.X (1927–28) – maximum continuous power, direct-drive left-hand tractor drive, compression ratio 6:1. * Kestrel IA, F.XIA (1927–28) – maximum continuous power, geared right-hand tractor drive, compression ratio 6:1. Production of new-built engines totalled 18. * Kestrel IB, F.XIB (1929–34) – maximum power at 2,700 rpm for 5 minutes using 77 octane fuel, maximum continuous power. Compression ratio 7:1. Production of new-built engines totalled 580. * Kestrel IB3, F.XIB3 (1934) – maximum continuous power, compression ratio 7:1. Production of new-built engines totalled 92. * Kestrel IB4, F.XIB4 (1934) – maximum continuous power, compression ratio 7:1. Production of new-built engines totalled 5. * Kestrel IB5, F.XIB5 (1934) – maximum continuous power, compression ratio 7:1. Production of new-built engines totalled 34. * Kestrel IMS, F.XIMS (1929) – maximum continuous power, medium supercharged, compression ratio 6:1. Production of new-built engines totalled 1. * Kestrel IS, F.XIS (1928–33) – maximum continuous power, fully supercharged, compression ratio 6:1. Production of new-built engines totalled 9. * Kestrel IIA, F.XIIA (1927–29) – maximum continuous power, compression ratio 6:1. Production of new-built engines totalled 31. * Kestrel IIB, F.XIIB (1933) – maximum continuous power, compression ratio 7:1. Production of new-built engines totalled 20. * Kestrel IIMS, F.XIIMS (1928–35) – maximum power at 2,700 rpm for 5 minutes using 77 octane fuel, maximum continuous power. Tractor drive, medium superchanged, compression ratio 5.5:1. Production of new-built engines totalled 82, some were later converted to pusher drive for the

Short Singapore The Short Singapore was a British multi-engined biplane flying boat built after the First World War. The design was developed into two four-engined versions: the prototype Singapore II and production Singapore III. The latter became the Royal ...

. * Kestrel IIMS.2, F.XIIMS.2 (1933–34) – maximum continuous power, medium superchanged, compression ratio 6:1. Production of new-built engines totalled 64. * Kestrel IIMS.5, F.XIIMS.5 (1934) – maximum power at 2,700 rpm using 77 octane fuel, maximum continuous power, medium superchanged, compression ratio 6:1. Production of new-built engines totalled 5. * Kestrel IIMS.6, F.XIIMS.6 (1935) – maximum continuous power, medium superchanged, compression ratio 6:1. Production of new-built engines totalled 16. * Kestrel IIS, F.XIIS (1928–38) – maximum power with boost at 2,750 rpm for 5 minutes using 77 octane fuel, maximum continuous power. Fully supercharged, compression ratio 6:1. Normally tractor drive, although versions fitted to the Gloster TC.33 were pusher drive. * Kestrel IIIB, F.XIVB – maximum continuous power, compression ratio 7:1. * Kestrel IIIMS, F.XIVMS (1933–35) – maximum continuous power, medium superchanged, compression ratio 5.5:1. Normally tractor drive, although versions fitted to the Short Singapore III were pusher drive. * Kestrel IIIMS.2, F.XIVMS.2 (1933–34) – maximum continuous power, medium superchanged, compression ratio 6:1. Production of new-built engines totalled 20. * Kestrel IIIMS.4, F.XIVMS.4 (1934) – maximum continuous power, medium superchanged, compression ratio 6:1. Production of new-built engines totalled 16. * Kestrel IIIMS.6, F.XIVMS.6 (1935) – maximum power with boost at 2,700 rpm for take off or 1 minute using 77 octane fuel, maximum continuous power. Medium superchanged, compression ratio 6:1. Production of new-built engines totalled 16. * Kestrel IIIS, F.XIVS (1930–38) – maximum power with boost at 2,700 rpm for take off or 1 minute using 77 octane fuel, maximum continuous power. Fully superchanged, compression ratio 6:1. Production of new-built engines totalled 71. * Kestrel IIIS.3, F.XIVS.3 (1934) – maximum continuous power, fully superchanged, compression ratio 6:1. Production of new-built engines totalled 48. * Kestrel IV (1935) – maximum continuous power, fully superchanged, compression ratio 6:1. Single engine built, it became the prototype

Rolls-Royce Goshawk The Rolls-Royce Goshawk was a development of the Rolls-Royce Kestrel that used evaporative or steam cooling. In line with Rolls-Royce convention of naming piston engines after birds of prey, it was named after the goshawk. The engine first ...

. * Kestrel V, V Spl. (1933–38) – maximum power with boost at 2,900 rpm using 87 octane fuel, maximum continuous power. Fully superchanged, compression ratio 6:1. Production of new-built engines totalled 1,178. * Kestrel VDR (1937) – maximum power with boost at 2,350 rpm using 77 octane fuel, maximum continuous power. Fully superchanged, compression ratio 6:1. * Kestrel VI (1934–1936) – maximum power with boost at 2,700 rpm for take off or 1 minute using 87 octane fuel, maximum continuous power. Fully superchanged, compression ratio 6:1. Production of new-built engines totalled 258. * Kestrel VII – maximum continuous power, medium superchanged, compression ratio 6:1. * Kestrel VIII (1936–37) – maximum continuous power, medium superchanged pusher drive, compression ratio 6:1. Production of new-built engines totalled 133. * Kestrel IX (1934–37) – maximum continuous power, medium superchanged tractor drive, compression ratio 6:1. Production of new-built engines totalled 136. * Kestrel X (1934–37) – maximum power at 2,900 rpm for 5 minutes using 87 octane fuel, maximum continuous power. Compression ratio 7:1. Production of new-built engines totalled 1,161. * Kestrel XDR (1937) – maximum continuous power, compression ratio 7:1. * Kestrel XI (1935–36) – maximum continuous power, compression ratio 7:1. Production of new-built engines totalled 55. * Kestrel XII – maximum continuous power, compression ratio 7:1. * Kestrel XIV – maximum continuous power, fully supercharged, compression ratio 6:1. * Kestrel XV – maximum continuous power, fully supercharged, compression ratio 6:1. * Kestrel XVI, XVI Spl. (1936–38) – maximum continuous power, fully supercharged, compression ratio 6:1. Production of new-built engines totalled 95. * Kestrel XVI (DR) (1937) – maximum continuous power, fully supercharged, compression ratio 6:1. * Kestrel XVI (VP) (1937) – maximum power with boost at 3,000 rpm for 5 minutes using 87 octane fuel, maximum continuous power. Fully supercharged, compression ratio 6:1. Converted from a Mk V for the Miles Kestrel. * Kestrel XXX (1938) – maximum power with boost at 2,750 rpm for take off or one minute using 87 octane fuel. Fully supercharged, compression ratio 6.2:1. Final Kestrel variant used in the

, they were manufactured by rebuilding older Kestrels, usually Mk Vs and Mk XVIs, with updated components.

Further Development

During 1927, once the prototype of the Kestrel was complete, a need for a larger and more powerful engine was conceived for use in flying boats, and development began on an engine which utilised a 6" cylinder bore, compared to the Kestrel's 5", this became the Rolls-Royce Buzzard. The Buzzard (or "H") engine was further modified for use in the Schneider Trophy as the Rolls-Royce R engine. In 1935 the Kestrel design was used as the basis to develop the

Rolls-Royce Merlin The Rolls-Royce Merlin is a British Coolant#Liquids, liquid-cooled V12 engine, V-12 Reciprocating engine, piston aero engine of 27-litre (1,650 cu in) Engine displacement, capacity. Rolls-Royce Limited, Rolls-Royce designed the engine an ...

. The Kestrel design was used as a base for both the

Goshawk Goshawk may refer to several species of birds of prey in the family Accipitridae: Palearctic * Eurasian goshawk, ''Astur gentilis'', often referred to simply as the goshawk, since it is the only goshawk found in much of its range (in Europe and ...

, however the aircraft which were intended to be fitted with the Goshawk engine were cancelled, so the project was scrapped. The Kestrel was also used as the basis for the Peregrine (and therefore the

Vulture A vulture is a bird of prey that scavenges on carrion. There are 23 extant species of vulture (including condors). Old World vultures include 16 living species native to Europe, Africa, and Asia; New World vultures are restricted to Nort ...

), all utilising the same 5" piston bore and 5.5" piston stroke. In practice, development of the Peregrine and Vulture engines were curtailed, before eventually being cancelled, to allow increased resource developing the Merlin engine during the war. As a response to the fuel injection systems developed by Bosch, in 1936 a Kestrel engine was fitted with a pressurised carburettor system to improve fuelling at high altitudes. The resulting behaviour of the engine when flight tested by the Farnborough institute was seen to be "...one of the smoothest engines they had used at high altitudes".The Secret Horsepower Race, p33

Applications

''From Lumsden, the Kestrel may not be the main power-plant for these types.'' ;Aircraft applications Miles Master

;Other applications * Speed of the Wind

Surviving airworthy engines

A handful of Rolls-Royce Kestrel engines remain airworthy as of March 2024, powering original or restored Hawker biplane types: *Hawker Hind (G-AENP) is owned and operated by

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 ...

in the UK. This suffered an issue in 2015 but has been rebuilt and installed back in to the Hind as of March 2024. *Hawker Demon (G-BTVE) with a Kestrel engine, which was resident at The Shuttleworth Collection in the UK, has been sold to an American collector as of March 2024. *Hawker Nimrod I (G-BWWK), ''S1581'', resides at IWM Duxford in the UK with The Fighter Collection. This aircraft is fitted with a Rolls-Royce Kestrel V. *Hawker Nimrod II (G-BURZ), ''K3661'', resides at IWM Duxford with the Historic Aircraft Collection and is fitted with a Rolls-Royce Kestrel VI. *Hawker Fury I (G-CBZP) with a Kestrel II engine resides at IWM Duxford with the Historic Aircraft Collection.

Engines on display

Preserved examples of the Rolls-Royce Kestrel engine are on public display at the: *

Australian National Aviation Museum The Moorabbin Air Museum is an aviation museum at Moorabbin Airport in Melbourne, Victoria, Australia. It was founded in 1962 as the Australian Aircraft Restoration Group, in an attempt to maintain a World War II-era Bristol Beaufighter aircr ...

Brooklands Museum Brooklands Museum is a motoring and aviation museum occupying part of the former Brooklands Motor Course in Weybridge, Surrey, England. Formally opened in 1991, the museum is operated by the independent Brooklands Museum Trust Ltd, a private l ...

The Hangar Flight Museum The Hangar Flight Museum, formerly known as the Aero Space Museum of Calgary, is a museum located south of Calgary International Airport in Calgary, Alberta, Canada. History The museum was founded in 1975 as the Aero Space Museum Association of C ...

Imperial War Museum Duxford Imperial War Museum Duxford, also known as IWM Duxford or simply Duxford, is a branch of the Imperial War Museum near Duxford in Cambridgeshire, England. Duxford, Britain's largest aviation museum, houses exhibits, including nearly 200 aircraf ...

Polish Aviation Museum The Polish Aviation Museum () is a large museum of historic aircraft and aircraft engines in Kraków, Poland. It is located at the site of the no-longer functional Kraków-Rakowice-Czyżyny Airport. This airfield, established by Austr ...

Cracow *

Rolls-Royce Heritage Trust The Rolls-Royce Heritage Trust is an organisation that was founded in 1981 to preserve the history of Rolls-Royce Limited, Rolls-Royce Holdings and all merged or acquired companies. Five volunteer led branches exist, three in England, one in Sco ...

Royal Air Force Museum Cosford The Royal Air Force Museum Midlands, located at RAF Cosford in Shropshire, is a free museum dedicated to the history of aviation and the Royal Air Force in particular. The museum is part of the Royal Air Force Museum, a non-departmental public ...

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 ...

Science Museum (London) The Science Museum is a major museum on Exhibition Road in South Kensington, London. It was founded in 1857 and is one of the city's major tourist attractions, attracting 3.3 million visitors annually in 2019. Like other publicly funded ...

* World of Wearable Arts and Classic Cars Museum (Nelson, NZ) * South Australian Aviation Museum Adelaide (Operational exhibit)

Specifications (Kestrel V)

References

Citations

Bibliography

* Erfurth, Helmut. ''Junkers Ju 87'' (Black Cross Volume 5). Bonn, Germany: Bernard & Graefe Verlag, 2004. . * * * Rubbra, A.A.''Rolls-Royce Piston Aero Engines - A Designer Remembers''. Rolls-Royce Heritage Trust. Historical Series no 16. 1990. * * * *

External links

Royal Air Force Museum - Rolls-Royce Kestrel
{{RRaeroengines

Kestrel The term kestrel (from , derivative from , i.e. ratchet) is the common name given to several species of predatory birds from the falcon genus ''Falco''. Kestrels are most easily distinguished by their typical hunting behaviour which is to hover ...

1920s aircraft piston engines V12 aircraft engines