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<document>
<title>Rolls-Royce Merlin</title>
<authors>Wikipedia</authors>
<publisher>wikipedia.org</publisher>
<publishedplace>network</publishedplace>
<publishedyear>2010</publishedyear>
<edition></edition>
<category>Featured articles</category>
<section id="8435" fatherid="0" title="" lv="" priority="-1" level="1">
The Rolls-Royce Merlin is a British, liquid-cooled, 27-litre (1,650 cu in) capacity, V-12 piston aero engine, designed and built by Rolls-Royce Limited. Initially known as the PV-12, Rolls-Royce named the engine the Merlin following the company convention of naming its piston aero engines after birds of prey.Gunston 1989, p. 137.
The PV-12 first ran in 1933, and a series of rapidly applied developments brought about by wartime needs improved the engine's performance markedly. The first operational aircraft to enter service using the Merlin were the Fairey Battle, Hawker Hurricane and Supermarine Spitfire. More Merlins were made for the four-engined Avro Lancaster heavy bomber than any other aircraft; however, the engine is most closely associated with the Spitfire and powered its maiden flight in 1936.
Considered an English icon,The Spitfire and Merlin icons.org.uk. Retrieved: 14 August 2009 the Merlin was one of the most successful aircraft engines of the World War II era, and many variants were built by Rolls-Royce in Derby, Crewe and Glasgow,Pugh 2000, pp. 192–198. as well as by Ford of Britain in Trafford Park, Manchester.Merlin Engines in Manchester bbc.co.uk. Retrieved: 14 August 2009 The Packard V-1650 was a version of the Merlin built in the United States. Production ceased in 1950 after a total of almost 150,000 engines had been delivered, the later variants being used for airliners and military transport aircraft.
In military use the Merlin was superseded by its larger capacity stablemate, the Rolls-Royce Griffon.  Merlin engines remain in Royal Air Force service today with the Battle of Britain Memorial Flight, and power many restored aircraft in private ownership worldwide.

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<section id="8436" fatherid="0" title="Design and development" lv="" priority="2" level="1">
<section id="8437" fatherid="8436" title="Origin" lv="" priority="1" level="2">
In the early 1930s, Rolls-Royce started planning its future aero engine development programme and realised that there was a need for an engine larger than their 21-litre (1,296 cu in) Kestrel that had been used with great success in a number of 1930s aircraft.Rubbra 1990, p. 64. Consequently, work was started on a new 1,100-horsepower (820 kW)-class design known as the PV-12, with PV standing for private venture as the company received no government funding for work on the project. The PV-12 was first run on 15 October 1933 and first flew in a Hawker Hart (K3036) biplane on 21 February 1935.Lumsden 2003, p. 203. The engine originally used the evaporative cooling system then in vogue.  This proved unreliable and when supplies of ethylene glycol from the U.S. became available, the engine was adapted to use a conventional liquid cooling system. The Hart was subsequently delivered to Rolls-Royce where, as a Merlin testbed, it completed over 100 hours of flying with the Merlin C and E engines.Mason 1991, p. 168.
In 1935, the Air Ministry issued a specification, F10/35, for new fighter aircraft with a minimum airspeed of 310 miles per hour (500 km/h). Fortunately, two designs had been developed: the Supermarine Spitfire and the Hawker Hurricane; the latter designed in response to another specification, F36/34.McKinstry 2007, p. 53. Both were designed around the PV-12 instead of the Kestrel, and were the only contemporary British fighters to have been so developed. Production contracts for both aircraft were placed in 1936, and development of the PV-12 was given top priority as well as government funding. Following the company convention of naming its piston aero engines after birds of prey, Rolls-Royce named the engine the Merlin after a small, Northern Hemisphere falcon (Falco columbarius).
Two more Rolls-Royce engines developed just prior to the war were added to the company's range. The 700-horsepower (500 kW) Rolls-Royce Peregrine was an updated, supercharged development of their V-12 Kestrel design, while the 1,700-horsepower (1,300 kW) 42-litre (2,560 cu in) Rolls-Royce Vulture was based on two joined Peregrines, using a common crankshaft and forming an X-24 cylinder layout. This was to be used in larger aircraft such as the Avro Manchester.Lumsden 2003, pp. 198–200.
Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature since Rolls-Royce's priority was refining the Merlin. As a result the Peregrine saw use in only two aircraft: the Westland Whirlwind and the Gloster F9/37. The Vulture was fitted to the Hawker Tornado and Avro Manchester, but proved unreliable in service.Lumsden 2003, p. 200. With the Merlin itself soon pushing into the 1,500-horsepower (1,100 kW) range, the Peregrine and Vulture were both cancelled in 1943, and by mid-1943 the Merlin was supplemented in service by the larger Rolls-Royce Griffon.Rubbra 1990, p. 118. The Griffon incorporated several design improvements and ultimately superseded the Merlin.

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<section id="8438" fatherid="8436" title="Development" lv="" priority="2" level="2">
<section id="8439" fatherid="8438" title="" lv="" priority="-1" level="3">
Initially the new engine was plagued with problems, such as failure of the accessory gear trains and coolant jackets, and several different construction methods were tried before the basic design of the Merlin was set.Rubbra 1990, pp. 64–117. Early production Merlins were also unreliable: common problems were cylinder head cracking, coolant leaks, and excessive wear to the camshafts and crankshaft main bearings.Rubbra 1990, pp. 82–92.
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<section id="8440" fatherid="8438" title="Early engines" lv="" priority="-2" level="3">
The prototype and developmental engine types were the:
The initial design using an evaporative cooling system. Two built, passed Type Testing in July 1934, generating 740 horsepower (552 kW) at 12,000 feet (3,657 m) equivalent. First flown 21 February 1935.
Two built, ethylene glycol liquid cooling system introduced. "Ramp" cylinder heads (inlet valves were at a 45-degree angle to the cylinder). Passed Type Testing February 1935, generating 950 horsepower (708 kW) at 11,000 feet (3,353 m) equivalent.
Crankcase and cylinder blocks became three separate castings with bolt-on cylinder heads.
Similar to C with minor design changes. Passed 50-hour civil test in December 1935 generating a constant 955 horsepower (712 kW) and a maximum rating of 1,045 horsepower (779 kW). Failed military 100-hour test in March 1936. Powered the Supermarine Spitfire prototype.Lumsden 2003, p. 204.
Similar to C and E. This became the first production engine; and was designated as the Merlin I. The Merlin continued with the "ramp" head, but this was not a success and only 172 were made. The Fairey Battle was the first production aircraft to be powered by the Merlin I and first flew on 10 March 1936.
Replaced "ramp" cylinder heads with parallel pattern heads (valves parallel to the cylinder) scaled up from the Kestrel engine. It was first widely delivered as the 1,030-horsepower (770 kW) Merlin II in 1938, and production was quickly stepped up.

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<section id="8441" fatherid="8438" title="Production engines" lv="" priority="3" level="3">
The Merlin II and III series were the first main production versions of the engine. The Merlin III was manufactured with a "universal" propeller shaft which allowed either de Havilland or Rotol manufactured propellers to be used.Fozard 1991, p. 125.
The next major version was the XX which ran on 100 octane fuel. This allowed higher manifold pressures, which were achieved by increasing the boost from the centrifugal type supercharger. The Merlin XX incorporated the two-speed superchargers designed by Rolls-Royce, resulting in increased power at higher altitudes than previous versions. Another improvement, which allowed the XX and future Merlin variants to run some  cooler, was the use of a 70/30% water/glycol coolant mix rather than the 100% glycol of the earlier versions. This substantially improved engine life and reliability, removed the fire hazard of the flammable ethylene glycol, and reduced the oil leaks that had been a problem with the early Merlin I, II and III series. Fozard 1991, pp. 127, 165.
The process of improvement continued, with later versions running on further-increased octane ratings, delivering ever higher power. Fundamental design changes were also made to all key components, again increasing the engine's life and reliability. By the end of the war the "little" engine was delivering over 1,600 horsepower (1,200 kW) in common versions, and as much as 2,060 horsepower (1,536 kW) in the Merlin 130/131 versions specifically designed for the de Havilland Hornet. Ultimately, during tests conducted by Rolls-Royce at Derby, Merlin 130 series engines generated over 2,600 horsepower (1,939 kW).Flight 1946, p. 93.

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<section id="8442" fatherid="8438" title="Basic component overview (Merlin 61)" lv="" priority="-4" level="3">
From Jane's:Bridgman 1998, pp. 280–281.
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<section id="8443" fatherid="8438" title="Technical improvements" lv="" priority="5" level="3">
<section id="8444" fatherid="8443" title="" lv="" priority="-1" level="4">
Most of the Merlin's technical improvements resulted from more efficient superchargers, designed by Stanley Hooker, and the introduction of aviation spirits with increased octane ratings. Numerous detail changes were made internally and externally to the engine to withstand increased power ratings and to incorporate advances in engineering practices.Lovesey 1946, pp. 224–226.
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<section id="8445" fatherid="8443" title="Ejector exhausts" lv="" priority="2" level="4">
In September 1937 the Spitfire prototype, K5054, was fitted with ejector type exhausts. Later marks of the Spitfire used a variation of this exhaust system fitted with forward-facing intake ducts to distribute hot air out to the wing-mounted guns to prevent freezing and stoppages at high altitudes, replacing an earlier system that used heated air from the engine coolant radiator. The latter system had become ineffective due to improvements to the Merlin itself which allowed higher operating altitudes where air temperatures are lower.Tanner 1981, A.P.1565E, Vol.1, Section II. Ejector exhausts were also fitted to other Merlin-powered aircraft.
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<section id="8446" fatherid="8443" title="Supercharger" lv="" priority="3" level="4">
Central to the success of the Merlin was the supercharger. A.C. Lovesey, an engineer who was a key figure in the design of the Merlin, delivered a lecture on the development of the Merlin in 1946; in this extract he explained the importance of the supercharger:
"Coming now to specific development items we can ... divide them into three general classes:
Dealing with (1) it can be said that the supercharger determines the capacity, or ... the output, of the engine. The impression still prevails that the static capacity known as the swept volume is the basis of comparison of the possible power output for different types of engine, but this is not the case because the output of the engine depends solely on the mass of air it can be made to consume efficiently, and in this respect the supercharger plays the most important role ... the engine has to be capable of dealing with the greater mass flows with respect to cooling, freedom from detonation and capable of withstanding high gas and inertia loads.... During the course of research and development on superchargers it became apparent to us that any further increase in the altitude performance of the Merlin engine necessitated the employment of a two-stage supercharger."Lovesey 1946, p. 218.
As the Merlin evolved so too did the supercharger; the latter fitting into three broad categories:Lumsden 2003, p. 201.
The Merlin supercharger was originally designed to allow the engine to generate maximum power at an altitude of about 16,000 feet (5,000 m). In 1938 Stanley Hooker, an Oxford graduate in applied mathematics, explained "...I soon became very familiar with the construction of the Merlin supercharger and carburettor.... Since the supercharger was at the rear of the engine it had come in for pretty severe design treatment, and the air intake duct to the impeller looked very squashed...." Tests conducted by Hooker showed the original intake design was inefficient, limiting the performance of the supercharger.Hooker 1984, p. 45. Hooker subsequently designed a new air intake duct with improved flow characteristics which increased maximum power at a higher altitude of over 19,000 feet (5800 m); and also improved the design of both the impeller, and the diffuser which controlled the airflow to it. These modifications led to the development of the single-stage Merlin XX and 45 series.Hooker 1984, pp. 46–50, 52, 235–247.
A significant advance in supercharger design was the incorporation in 1938 of a two-speed drive, designed by the French company Farman, to the impeller of the Merlin X.Lumsden 2003, p. 206. The later Merlin XX incorporated the two-speed drive as well as several improvements that enabled an increase in the production rate of Merlins.Smith February 1942 p. b. The low-ratio gear, which operated from take-off to an altitude of 10,000 feet (3,050 m), drove the impeller at 21,597 rpm and developed 1,240 horsepower (925 kW) at that height; while the high gear's (25,148 rpm) power rating was 1,175 horsepower (876 kW) at 18,000 feet (5,490 m). These figures were achieved at 2,850 rpm engine speed using +9 pounds per square inch (1.66 atm) boost.Smith February 1942 p. d.
In 1940 Rolls-Royce considered adapting the Merlin to use an exhaust-driven turbocharger to increase the power of the Merlin. Although a lower fuel consumption was an advantage, the turbocharger was rejected in favour of a two-stage supercharger.Lovesey 1946, p. 219. The basic design, first tested in September 1941, used a modified Vulture supercharger for the first stage while a Merlin 46 supercharger was used for the second.Lovesey 1946, p. 220. A liquid-cooled intercooler on top of the supercharger casing was used to prevent the compressed air/fuel mixture from becoming too hot. Fitted with the two-stage two-speed supercharger, the Merlin 60 series gained 300 horsepower (224 kW) at 30,000 feet (9,144 m) over the Merlin 45 series, at which altitude a Spitfire IX was nearly 70 miles per hour (113 km/h) faster than a Spitfire V.Price 1982, pp. 142, 167.
The two-stage Merlin family was extended in 1943 with the Merlin 66 which had its supercharger geared for increased power ratings at low altitudes, and the Merlin 70 series that were designed to deliver increased power at high altitudes.Price 1982, pp. 153-154, 170.
The development in 1942 of the single-stage supercharger with a smaller "cropped" impeller resulted in the Merlin 45M and 55M, both of which developed greater power at low altitudes.Lumsden 2003, p. 210. In squadron service the LF.V variant of the Spitfire fitted with these engines became known as the "clipped, clapped and cropped Spitty" to indicate the shortened wingspan, the less-than-perfect condition of the used airframes and the cropped supercharger impeller.Price 1982, p. 135.

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<section id="8447" fatherid="8443" title="Carburettor developments" lv="" priority="4" level="4">
The use of carburettors was calculated to give a higher specific power output, due to the lower temperature, hence greater density, of the fuel/air mixture compared to injected systems.Hooker 1984, p. 62. However, the Merlin's lack of direct fuel injection meant that both Spitfires and Hurricanes were unable to pitch nose down into a steep dive. The contemporary Bf 109E, which had direct fuel injection, could "bunt" into a high-power dive to escape attack, leaving the pursuing aircraft behind because its fuel had been forced out of the carburettor's float chamber by the effects of negative g-force (g). RAF fighter pilots soon learned to "half-roll" their aircraft before diving to pursue their opponents.McKinstry 2007, p. 205. "Miss Shilling's orifice", a holed diaphragm fitted across the float chambers, went some way towards curing the fuel starvation in a dive; however, at less than maximum power a "fuel rich" mixture still resulted. Another improvement was made by moving the fuel outlet from the bottom of the S.U. carburettor to exactly halfway up the side, which allowed the fuel to flow equally well under negative or positive g.Smallwood 1996, p. 135.
Further improvements were introduced throughout the Merlin range: 1943 saw the introduction of a Bendix-Stromberg pressure carburettor that injected fuel at 5 pounds per square inch (0.34 bar) through a nozzle directly into the supercharger, and was fitted to Merlin 66, 70, 76, 77 and 85 variants. The final development, which was fitted to the 100-series Merlins, was an S.U. injection carburettor that injected fuel into the supercharger using a fuel pump driven as a function of crankshaft speed and engine pressures.Lumsden 2003, p. 212.

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<section id="8448" fatherid="8443" title="Improved fuels" lv="" priority="-5" level="4">
At the start of the war the engine ran on the then standard 87 octane aviation spirit and could supply just over 1,000 horsepower (750 kW) from its 27-litre displacement: the maximum boost pressure at which the engine could be run using 87 octane fuel was +6 pounds per square inch (1.45 atm). However, as early as 1938, at the 16th Paris Air Show, Rolls-Royce displayed two versions of the Merlin rated to use 100 octane fuel. The Merlin R.M.2M was capable of 1,265 horsepower (943 kW) at 7,870 feet (2,400 m), 1,285 horsepower (958 kW) at 9,180 feet (2,800 m) and 1,320 horsepower (984 kW) on take-off; while a Merlin X with a two-speed supercharger in high gear generated 1,150 horsepower (857 kW) at 15,400 feet (4,700 m) and 1,160 horsepower (865 kW) at 16,730 feet (5,100 m).Flight 1938, p. 528.
From late-1939, 100 octane fuel became available from the U.S., West Indies, Persia and domestically.Payton-Smith 1971, pp. 259–260.  Merlin IIs and IIIs were adapted to run on the new fuel, using an increased boost pressure of +12 pounds per square inch (1.85 atm). Small modifications were made to the engines which were now capable of generating 1,310 horsepower (877 kW) at   while running at 3,000 revolutions per minute.Gunston, p. 144. This increased boost was available for a maximum of five minutes, and if the pilot resorted to emergency boost he had to report this on landing and have it noted in the engine log book. Using +12 pounds per square inch (1.85 atm) of boost was considered a "definite overload condition on the engine" and the engineering officer was subsequently required to examine the engine and reset the throttle gate.Air Ministry 1940.
In late-1943 trials were run of a new "100/150" grade fuel, recognised by its b-green colour and "awful smell".McKinstry 2007, p. 356. Initial tests were conducted using 6.5 cubic centimetres of tetraethyl lead (T.E.L.) for every one gallon of 100 octane fuel; but this mixture resulted in a build-up of lead in the combustion chambers, causing excessive fouling of the spark plugs. Better results were achieved by adding 2.5% mono methyl aniline (M.M.A.) to 100 octane fuel.Lovesey 1946, pp. 222–223. The new fuel allowed the boost rating of the Merlin 66 to be raised to +25 pounds per square inch (2.79 atm).Price 1982. p. 170.
Starting in March 1944, the Merlin 66-powered Spitfire IXs of two squadrons were cleared to use the new fuel for operation trials, and it was put to good use in the summer of 1944 when it enabled Spitfire L.F. Mk. IXs to intercept V-1 flying bombs coming in at low altitudes, as well as by other fighters flown by the ADGB, but continued problems with backfires were not remedied until August.
In early February 1945, Spitfires of the 2 TAF also began using 100/150 grade fuel.Berger -anddocsymbol- Street 1994. p. 199. Monty Berger, Senior Intelligence Officer of 126 (RCAF) Spitfire Wing, 2 TAF, noted that there were still problems being experienced with the new fuel, leading to several fatal accidents. Pilots were relieved when the return to 130 grade was authorised by April 1945.

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<section id="8449" fatherid="0" title="Production" lv="" priority="3" level="1">
<section id="8450" fatherid="8449" title="" lv="" priority="-1" level="2">
Production of the Rolls-Royce Merlin was driven by the forethought and determination of Ernest Hives, who at times was enraged by the apparent complacency and lack of urgency encountered in his frequent correspondence with Air Ministry and local authority officials. Hives was an advocate of shadow factories, and sensing the imminent outbreak of war pressed ahead with plans to produce the Merlin in sufficient numbers for the rapidly expanding Royal Air Force. Despite the importance of uninterrupted production several factories were affected by industrial action.McKinstry 2007, pp. 327–329.
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<section id="8451" fatherid="8449" title="Derby" lv="" priority="2" level="2">
The existing Rolls-Royce facilities at Osmaston, Derby were not suitable for large-scale engine production although the floor space had been increased by some 25% between 1935 and 1939; nevertheless, Hives planned to build the first two- or three hundred engines there until engineering teething troubles had been resolved. Having a workforce that consisted mainly of design engineers and highly skilled men, the Derby factory carried out the majority of development work on the Merlin, with flight testing carried out at nearby RAF Hucknall. The original factory closed in March 2008, but Rolls-Royce plc still maintains a large presence in Derby.Derby factory closure news.bbc.co.uk. Retrieved: 24 August 2009
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<section id="8452" fatherid="8449" title="Crewe" lv="" priority="3" level="2">
To meet the increasing demand for Merlin engines, Rolls-Royce started building work on a new factory at Crewe in May 1938, with engines leaving the factory in 1939. The Crewe factory had convenient road and rail links to their existing facilities at Derby. Production at Crewe was originally planned to use unskilled labour and sub-contractors with which Hives felt there would be no particular difficulty, but the number of required sub-contracted parts such as crankshafts, camshafts and cylinder liners eventually fell short and the factory was expanded to manufacture these parts "in house".Pugh 2000, p. 193.
Initially the local authority promised to build 1,000 new houses to accommodate the workforce by the end of 1938, but by February 1939 it had only awarded a contract for 100. Hives was incensed by this complacency and threatened to move the whole operation, but timely intervention by the Air Ministry improved the situation. In 1940 a strike took place when women replaced men on capstan lathes, the workers' union insisting that this was a skilled labour job; however, the men returned to work after 10 days.Pugh 2000, pp. 196–197. Post-war the factory was used for the production of Bentley motor cars, and in 1998 Volkswagen AG bought both the marque and the factory.Crewe factory history jackbarclayparts.co.uk. Retrieved: 24 August 2009

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<section id="8453" fatherid="8449" title="Glasgow" lv="" priority="4" level="2">
Hives further recommended that a factory be built near Glasgow to take advantage of the abundant local work force and the supply of steel and forgings from Scottish manufacturers. This government-funded and -operated factory was built at Hillington starting in June 1939 with workers moving into the premises in October, one month after the outbreak of war, the factory becoming fully occupied by September 1940. A housing crisis also occurred at Glasgow where Hives again asked the Air Ministry to step in.Pugh 2000, p. 197.
Having 16,000 employees, the Glasgow factory was one of the largest industrial operations in Scotland. Unlike the Derby and Crewe plants which relied significantly on external subcontractors, it produced almost all the Merlin's components itself.Lloyd -anddocsymbol- Pugh 2004, p. 61. Engines began to leave the production line in November 1940, and by June 1941 monthly output had reached 200, increasing to more than 400 per month by March 1942.Lloyd -anddocsymbol- Pugh 2004, p. 69. In total 23,675 engines were produced. Worker absenteeism became a problem after some months due to the physical and mental effects of wartime conditions such as the frequent occupation of air-raid shelters. It was agreed to cut the punishing working hours slightly to 82 hours a week, with one half-Sunday per month awarded as holiday.Pugh 2000, p. 198. Record production is reported to have been 100 engines in one day.End of era for Rolls-Royce plant. news.bbc.co.uk. Retrieved: 25 August 2009
Immediately after the war the site repaired and overhauled Merlin and Griffon engines, and continued to manufacture spare parts. Finally, following the production of the Rolls-Royce Avon turbojet and others, the factory was closed in 2005.Hillington factory history rolls-royce.com. Retrieved: 24 August 2009

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<section id="8454" fatherid="8449" title="Manchester" lv="" priority="5" level="2">
The Ford Motor Company was asked to produce Merlins at Trafford Park, Manchester, and building work on a new factory was started in May 1940 on a  site. Built with two distinct sections to minimise potential bomb damage, it was completed in May 1941 and bombed in the same month. At first, the factory had difficulty in attracting suitable labour, and large numbers of women, youths and untrained men had to be taken on. Despite this, the first Merlin engine came off the production line one month laterNicholls 1996, p. 103. and it was building the engine at a rate of 200 per week by 1943, at which point the joint factories were producing 18,000 Merlins per year. In his autobiography Not much of an Engineer,  Sir Stanley Hooker states: "... once the great Ford factory at Manchester started production, Merlins came out like shelling peas ...".Hooker 1984, pp. 58–59.
Some 17,316 people worked at the Manchester plant, including 7,260 women and two resident doctors and nurses. Merlin production started to run down in August 1945, and finally ceased on 23 March 1946.Nicholls 1996, p. 105.

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<section id="8455" fatherid="8449" title="Packard V-1650" lv="" priority="6" level="2">
As the Merlin was considered to be so important to the war effort, negotiations were soon started to establish an alternative production line outside the UK. Rolls-Royce staff visited a number of North American automobile manufacturers in order to select one to build the Merlin in the U.S. or Canada. Henry Ford rescinded an initial offer to build the engine in the U.S. in July 1940, and the Packard Motor Car Company was subsequently selected to take on the $130,000,000 Merlin order.Time Magazine (8 July 1940) – Business: Ford's Rolls-Royces. time.com. Retrieved: 26 August 2009 Agreement was reached in September 1940, and the first Packard-built engine, designated V-1650-1, ran in August 1941.Lumsden 2003, p. 202.
By the end of its production run in 1950, almost 150,000 Merlin engines had been built; over 112,000 in Britain and more than 37,000 under license in the U.S.

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<section id="8456" fatherid="0" title="Variants" lv="" priority="4" level="1">
This is a summary list of representative Merlin variants. Engines of the same power output were typically assigned different model numbers based on supercharger or propeller gear ratios, differences in cooling system or carburettors, engine block construction, or arrangement of engine controls.Bridgman 1998, p. 283. All but the Merlin 131 and 134 engines were "-hand tractor", i.e. the propeller rotated to the  when viewed from the rear.
Data from Bridgman (Jane's)Bridgman 1998, pp. 281–283. unless otherwise noted:
1,030 hp (775 kW) at 3,000 rpm at 5,500 ft (1,680 m) using + 6 lb boost (1.45 atm); Merlin III fitted with "universal" propeller shaft able to mount either de Havilland or Rotol propellers,Robertson 1973, p. 144.
1,310 hp (977 kW) at 3,000 rpm at  with 100 octane fuel and +12 lb (1.85 atm)  boost  (Merlin III);Harvey-Bailey 1995, p. 155. both used in Spitfire Mk.I and Hurricane Mk.I fighters, the Boulton Paul Defiant, and Fairey Battle.Bridgman 1998, p. 281.
1,130 hp (840 kW) at 3,000 rpm at 5,250 ft (1,525 m); used in Halifax Mk.I, Wellington Mk.II, and Whitley Mk.V bombers.
1,150 hp (860 kW); fitted with Coffman engine starter; first version to use 70/30% water/glycol coolant rather than 100% glycol. Fitted to Spitfire Mk. II.
1,480 hp (1,105 kW) at 3,000 rpm at 6,000 ft (1,830 m); used in Hurricane Mk.II and Beaufighter Mk.II fighters, Halifax Mk.II and Lancaster Mk.I bombers.
1,645 hp (1,230 kW) at 3,000 rpm at 2,500 ft (760 m); used mainly in Fleet Air Arm aircraft; used in Barracuda Mk.II torpedo bomber and Seafire IIc. Also Spitfire P.R Mk XIII.
1,515 hp (1,130 kW) at 3,000 rpm at 11,000 ft (3,353 m); used in Spitfire Mk.V, PR.Mk.IV and PR.Mk.VII, Seafire Ib and IIc.
1,415 hp (1,055 kW) at 3,000 rpm at 14,000 ft (4,270 m); high-altitude version used in Spitfire H.F Mk VI. Adapted with a Marshall compressor (often called a "blower") to pressurise the cockpit.
1,585 hp (1,182 kW) at 3,000 rpm at 3,800 ft (1,160 m); low-altitude version with supercharger impeller "cropped" to  in diameter. Permitted boost was +18 lb (2.3 atm) instead of +16 lb (2.15 atm) on a normal Merlin 50 engine. A "negative-g" carburettor was fitted.Robertson 1973, p. 145.Price 1982, p. 145.
1,565 hp (1,170 kW) at 3,000 rpm at 12,250 ft (3,740 m)
1,390 hp (1,035 kW) at 3,000 rpm at 23,500 ft (7,170 m); fitted with a new two-speed two-stage supercharger providing increased power at medium to high altitudes; used in Spitfire F. Mk IX, and P.R.Mk XI.Smith 1942,  pp. 655–659. First British production variant to incorporate two-piece cylinder blocks designed by Rolls-Royce for Packard Merlin.Smith 1942, p. 656.
1,720 hp (1,283 kW) at 5,750 ft (1,752 m) using +18 lb boost (2.3 atm); low-altitude version of Merlin 61. Fitted with a Bendix-Stromberg anti-g carburettor;Air Ministry 1943, p. 6. used in Spitfire L.F Mk VIII and L.F Mk IX.
1,233 hp (920 kW); used in the Westland Welkin high-altitude fighter and some later Spitfire and Mosquito variants. Fitted with a two-speed, two-stage supercharger and a Bendix-Stromberg carburettor. The odd-numbered mark drove a blower for pressurising the cockpit.
2,060 hp (1,536 kW); redesigned "slimline" versions for the de Havilland Hornet. Engine modified to decrease frontal area to a minimum and was the first Merlin series to use down-draught induction systems. Coolant pump moved from the bottom of the engine to the starboard side. Two-speed, two-stage supercharger and S.U. injection carburettor. Maximum boost was 25 lb (2.79 atm). The Merlin 131 had an additional idler gear in the reduction gear casing allowing "reverse" (-hand tractor) rotation. The Merlin 130 was fitted in the starboard nacelle, Merlin 131 in the port nacelle on production Hornets.Flight 1946, pp. 92–94.
2,030 hp (1,514 kW); derated variants of 130/131 used in Sea Hornet F. Mk. 20, N.F. Mk. 21 and P.R. Mk. 22. Maximum boost was lowered to +18 lb (2.3 atm).
The prefix "2" indicates engines built by Packard, otherwise as Merlin 66, optimised for low-altitude operation.  Fitted to the Spitfire Mk. XVI.

</section>
<section id="8457" fatherid="0" title="Applications" lv="" priority="-5" level="1">
<section id="8458" fatherid="8457" title="" lv="" priority="-1" level="2">
In chronological order, the first operational aircraft powered by the Merlin to enter service were the Fairey Battle, Hawker Hurricane and Supermarine Spitfire.Lumsden 2003, p. 205. Although the engine is most closely associated with the Spitfire, the four-engined Avro Lancaster was the most numerous application, followed by the twin-engined de Havilland Mosquito.Lumsden 2003, pp. 208–209.
</section>
<section id="8459" fatherid="8457" title="Aircraft list" lv="" priority="2" level="2">
List from Lumsden 2003 Lumsden 2003, pp. 203–215.
</section>
<section id="8460" fatherid="8457" title="Postwar" lv="" priority="-3" level="2">
At the end of World War II, new versions of the Merlin (the 600- and 700-series) were designed and produced for use in commercial airliners such as the Avro Tudor, military transport aircraft such as the Avro York, and the Canadair North Star which performed in both roles. These engines were basically military specification with some minor changes to suit the different operating environment.Lumsden 2003, pp. 214–215.
A Spanish-built version of the Messerschmitt Bf 109 G-2, the 1954 Hispano Aviación HA-1112-M1L Buchon, was built in Hispano's factory in Seville with the Rolls-Royce Merlin 500/45 engine of  – a fitting powerplant for the last-produced version of the famous Messerschmitt fighter, as the Bf 109 V1 prototype aircraft had been powered by the Rolls-Royce Kestrel V-12 engine in 1935.Lumsden 2003, p. 214.
The CASA 2.111 was another Spanish-built version of a German aircraft, the Heinkel He 111, that was adapted to use the Merlin after the supply of Junkers Jumo 211F-2 engines ran out at the end of the war.Wilson, Randy. It's a Heinkel: the Luftwaffe's workhorse Heinkel 111 bomber rwebs.net, The Dispatch. Volume 12, Number 4, Winter 1996. Retrieved: 6 September 2009 A similar situation existed with the Fiat G.59 when available stocks of the Italian licence-built version of the Daimler-Benz DB 605 engine ran short.Green -anddocsymbol- Swanborough 1994, p. 211.
In the United States many war surplus engines and airframes were sold relatively cheaply – two of the most popular items were P-51 Mustangs and Packard V-1650 Merlin engines, several of which were "souped up" and modified for air racing in the Bendix Trophy, the Cleveland Air RacesCleveland Air Races airracinghistory.freeola.com. Retrieved: 4 September 2009 and the Thompson Trophy.

</section>
<section id="8461" fatherid="8457" title="Alternative applications" lv="" priority="-4" level="2">
A non-supercharged version of the Merlin using a larger proportion of steel and iron components was produced for use in tanks. This engine, the Rolls-Royce Meteor, in turn led to the smaller Rolls-Royce Meteorite.Pugh 2000, p. 254.
In 1938, Rolls-Royce started work on modifying some Merlins which were later to be used in British MTBs, MGBs, and RAF Air-Sea Rescue Launches. For these the superchargers were modified single-stage units and the engine was re-engineered for use in a marine environment.Marine history. rolls-royce.com. Retrieved: 21 August 2009

</section>
</section>
<section id="8462" fatherid="0" title="Survivors" lv="" priority="-6" level="1">
One of the most successful of the World War II era aircraft engines, the Merlin continues to be used in many restored World War II vintage aircraft all over the world. The Royal Air Force Battle of Britain Memorial Flight is a notable current operator of the Merlin. In England the Shuttleworth Collection owns and operates a Merlin-powered Hawker Sea Hurricane IB and a Supermarine Spitfire VC – the Hurricane can be seen flying at home displays throughout the summer months, while the Spitfire is currently undergoing a major restoration project.Shuttleworth Collection - Hawker Sea Hurricane IB shuttleworth.org. Retrieved: 14 August 2009Shuttleworth Veteran Aeroplane Society (SVAS) - Spitfire restoration svasweb.org. Retrieved: 14 August 2009
</section>
<section id="8463" fatherid="0" title="Engines on display" lv="" priority="7" level="1">
Many aerospace museums possess examples of the Merlin that are on public display, including the:
</section>
<section id="8464" fatherid="0" title="Specifications (Merlin 61)" lv="" priority="-8" level="1">
</section>
<section id="8465" fatherid="0" title="See also" lv="" priority="-9" level="1">
</section>
<section id="8466" fatherid="0" title="References" lv="" priority="-10" level="1">
<section id="8467" fatherid="8466" title="Footnotes" lv="" priority="-1" level="2">
</section>
<section id="8468" fatherid="8466" title="Citations" lv="" priority="-2" level="2">
</section>
<section id="8469" fatherid="8466" title="Bibliography" lv="" priority="-3" level="2">
</section>
</section>
<section id="8470" fatherid="0" title="Further reading" lv="" priority="-11" level="1">
</section>
<section id="8471" fatherid="0" title="External links" lv="" priority="-12" level="1">
Merlin
Category:Aircraft piston engines 1930-1939

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