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Rolls-Royce Merlin

From PlaneSpottingWorld, for aviation fans everywhere

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. Rolls-Royce named the engine the Merlin following the company convention of naming its piston aero engines after birds of prey.[1]

First run in 1933 and initially known as the PV-12, a series of rapidly applied developments, brought about by wartime needs, improved performance markedly. In military use the Merlin was eventually superceded by its larger capacity stablemate, the Rolls-Royce Griffon. Powering the Supermarine Spitfire on its maiden flight in 1936, the Merlin is probably best remembered for its association with this equally renowned aircraft.

Many variants of the Merlin were built by Rolls-Royce in Derby, Crewe and Glasgow,[2] as well as by Ford of Britain in Trafford Park, Manchester.[3] 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 last variants being used for airliners and military transport aircraft.

Considered to be an English icon,[4] the Merlin was one of the most successful of the World War II era aircraft engines. Merlin engines remain in Royal Air Force service today with the Battle of Britain Memorial Flight and also power many restored aircraft in private ownership worldwide.


Design and development


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.[5] 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 money for work on the project. The PV-12 first flew in a Hawker Hart (K3036) biplane on 21 February 1935,[6] using the evaporative cooling system then in vogue, but this proved unreliable and so, 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.[7]

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.[8] Both were designed around the PV-12 instead of the Kestrel, and were the only modern British fighters to have been so developed. Production contracts for both aircraft were placed in 1936, and the PV-12 was given top priority. 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).[nb 1][1]

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.

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.[9] 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 which incorporated several design improvements.[10]


Initially the new engine was plagued with problems, such as failure of the accessory gear trains and constant failure of the coolant jackets, and several different construction methods were tried before the basic design of the Merlin was set.[11]

Prototype engines

The prototype engine types were the:

  • PV-12
The initial design using an evaporative cooling system. Passed Type Testing in June 1934, generating 740 horsepower (552 kW) at 12,000 feet (3,657 m) equivalent.
  • Merlin B
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.
  • Merlin C
Crankcase and cylinder blocks became three separate castings with bolt-on cylinder heads.
  • Merlin E
Similar to C with minor design changes. Passed 50-hour civil test generating a constant 955 horsepower (712 kW) and a maximum rating of 1,045 horsepower (779 kW).
Parallel valve Merlin cylinder head
  • Merlin F
Similar to C and E. This became the first production engine; built 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.
  • Merlin G
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.

Early production Merlins were also unreliable; known problems were cylinder head cracking, coolant leaks, and excessive wear to the camshafts and the crankshaft main bearings.[12]

Basic component overview (Merlin 61)

From Jane's:[13]

Twelve cylinders consisting of high-carbon steel liners set in two, two-piece cylinder blocks of cast "R.R.50" aluminium alloy having separate heads and skirts. Coolant in direct contact with external face of liners. Cylinder heads fitted with cast-iron inlet valve guides, phosphor bronze exhaust valve guides, and renewable "Silchrome" steel-alloy valve seats. Two diametrically opposed spark plugs protrude into each combustion chamber.
Machined from "R.R.59" alloy forgings. Fully-floating hollow gudgeon pins of hardened nickel-chrome steel. Three compression and one oil-control ring above the gudgeon pin, and one oil-control ring below.
Connecting rods
H-section machined nickel-steel forgings, each pair consisting of a plain and a forked rod. The forked rod carries a nickel-steel bearing block which accommodates steel-backed lead-bronze-alloy bearing shells. The "small-end" of each rod houses a floating phosphor bronze bush.
One-piece, machined from a nitrogen-hardened nickel-chrome molybdenum steel forging. Statically and dynamically balanced. Seven main bearings and six throws.
Two aluminium-alloy castings joined together on the horizontal centreline. The upper portion bears the wheelcase, supercharger and accessories; and carries the cylinder blocks, crankshaft main bearings (split mild-steel shells lined with lead–bronze alloy), and part of the housing for the airscrew reduction gear. The lower half forms an oil sump and carries the oil pumps and filters.
Aluminium casting fitted to rear of crankcase. Houses drives to the camshafts, magnetos, coolant and oil pumps, supercharger, hand and electric starters, and the electric generator.
Valve gear
Two inlet and two exhaust poppet valves of "K.E.965" steel per cylinder. Both the inlet and exhaust valves have hardened "stellited" ends; while the exhaust valves also have sodium-cooled stems, and heads protected with a "BrightRay" (nickel-chromium) coating. Each valve is kept closed by a pair of concentric coil-springs. A single, seven-bearing camshaft, located on the top of each cylinder head operates 24 individual steel rockers; 12 pivoting from a rocker shaft on the inner, intake side of the block to actuate the exhaust valves, the others pivoting from a shaft on the exhaust side of the block to actuate the intake valves.

Technical improvements

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.[14]

Ejector exhausts

In September 1937 the Spitfire prototype, K5054, was fitted with Rolls-Royce -designed ejector type exhausts. The Merlin consumed an enormous volume of air at full power (equivalent to the volume of a single-decker bus per minute), and with the exhaust gases exiting at 1,300 miles per hour (2,100 km/h) it was realised that useful thrust could be gained simply by angling the gases backwards instead of venting sideways.

Merlin ejector exhaust detail

Test engineers noted the figure of 70 pounds-force (32 kgf) thrust at 300 miles per hour (480 km/h), or roughly 70 horsepower (52 kW) which increased the level maximum speed of the Spitfire by 10 miles per hour (16 km/h) to 360 miles per hour (580 km/h).[15] The ejector exhausts were also fitted to other Merlin-powered aircraft. The first versions of the ejector exhausts featured round outlets, subsequent versions of the system used "fishtail" style outlets which marginally increased thrust while reducing exhaust glare for night flying.

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 the temperatures are resultingly lower.[16]


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, for convenience, divide them into three general classes:

  1. Improvement of the supercharger.
  2. Improved fuels.
  3. Development of mechanical features to take care of the improvements afforded by (1) and (2).

Dealing with (1) it can be said that the supercharger determines the capacity, or in other words 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. This applies equally to any engine but 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."[17]

As the Merlin evolved so too did the supercharger; the latter fitting into three broad categories:[18]

  1. Single-stage, single-speed gearbox: Merlin variants; Merlin I to III, XII, 30, 40, 50 series.
  2. Single-stage, two-speed gearbox: Experimental Merlin X 1938, Merlin XX 1940–1945.
  3. Two-stage, two-speed gearbox with intercooler: Mainly Merlin 60, 70, 80 series 1942–1946.

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). However, according to Stanley Hooker, an Oxford graduate in applied mathematics, there were problems with the first supercharger design:

"Back in 1938 I soon became very familiar with the construction of the Merlin supercharger and carburettor. The engine had been designed to fit the Hurricane and Spitfire fighters, and its length had been compressed as much as possible to match the fore-and-aft balance on these aircraft. 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...[19]

The function of the supercharger is to compress the fuel/air mixture entering the engine cylinders, and any pressure loss to the impeller[nb 2] would impair the supercharger's efficiency. Hooker conducted experiments that showed the original intake design was inefficient, limiting the performance of the supercharger. He also improved the design of both the impeller, and the diffuser which led to it. These modifications improved the flow characteristics of the air inlet which increased the output power at altitude,[nb 3] markedly improved the efficiency of the supercharger, and led to the development of the Merlin XX and 45 series.[20]

Another new development was the incorporation of a two-speed drive for the supercharger of the Merlin X.[21] In 1938 Rolls-Royce took out a license to build the two-speed drive designed by the French company Farman.[22]

Carburettor developments
File:Packard Merlin V1650 7 3.jpg
Carburettor, supercharger and intercooler detail of a preserved Packard V-1650-7 (Merlin 66)

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.[23] 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.[24] "Miss Shilling's orifice",[nb 4] 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.[25]

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.[26]

Improved fuels

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 (0.41 atm).[nb 5] 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 blower 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), with the supercharger in high gear.[27]

From late-1939, 100 octane fuel became available from the U.S., West Indies, Persia and domestically.[28] Merlin IIs and IIIs were adapted to run on the new fuel, using an increased boost pressure of +12 pounds per square inch (0.82 atm). Small modifications were made to the engines which were now capable of generating 1,310 horsepower (877 kW) at 9,000 feet (2,700 m) while running at 3,000 revolutions per minute.[29][30] 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 (0.82 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.[31]

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 first of the two-speed superchargers designed by Rolls-Royce. The result was 1,300 horsepower (970 kW) at higher altitudes than previous versions. Another improvement made to the XX and future Merlin variants was the use of a 70/30% water/glycol coolant mix rather than the 100% glycol of the earlier versions, allowing them to run some 70 degrees C cooler. 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.[32]

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 (1,544 kW) in the Merlin 130/131 versions used on the de Havilland Hornet; during tests conducted by Rolls-Royce at Derby Merlin 130/131s generated over 2,600 horsepower (1,939 kW).[33]

In late-1943 trials were run of a new "100/150" grade fuel, recognised by its bright-green colour and "awful smell".[34] 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.[35]

The new fuel allowed the boost rating of the Merlin 66 to be raised to +25 pounds per square inch (1.7 atm).[36] 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,[36] 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.[37] 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.[37]

P-51B Mustang aircraft of the U.S. 8th Air Force fitted with V-1650-7 (Merlin 66) engines were running on 100/150 grade by the second week of June 1944; however, problems continued to be experienced with fouled spark plugs. To counter this a new blend of fuel called P.E.P., using ethylene dibromide, was introduced in early-1945, but use of this fuel was discontinued in March and 8th AF units reverted to the standard 100/150 grade.[38]


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.


The existing Rolls-Royce facilities at Derby were not suitable for large scale engine production although the floor space had been increased by some 25% between 1935 and 1939; however, Hives planned to build the first two or three hundred engines there until engineering 'teething troubles' had been resolved. The Derby factory carried out the majority of development work on the Merlin, having a workforce that consisted mainly of design engineers and highly skilled men, with flight testing carried out at nearby RAF Hucknall.

Rolls-Royce plc maintains a large presence in Derby but the original factory was closed in March 2008.[39]


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. 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'.

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 worker's union insisting that this was a skilled labour job; however, the men returned to work after 10 days.[40] 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.[41]


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, Glasgow 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.[42]

Having 16,000 employees, the factory was one of the largest industrial operations in Scotland, with engines beginning to leave the line in November 1940. By the start of the Battle of Britain 2,000 Merlins had been produced at Hillington, the final total being 23,675. Worker absenteeism became a problem after some months due to the physical and mental effects of wartime conditions such as 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.[43] Record production is reported to have been 100 engines in one day.[44]

Immediately after the war the site repaired and overhauled Merlin and Griffon engines, and continued to manufacture spare parts.[44] Finally, following the production of the Rolls-Royce Avon turbojet and others, the factory was closed in 2005.[45]


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 118-acre site. Built with two distinct sections to minimise bomb damage, it was completed in May 1941 and bombed in the same month. At first, the factory had difficulties 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 later[46] 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.[18] 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...".[47]

Some 17,316 people worked at the Manchester plant, including 7,260 women and two resident doctors and nurses.[46] Merlin production started to run down in August 1945, and finally ceased on 23 March 1946.[48]

Packard V-1650

Main article: Packard V-1650

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.[nb 6][49] Agreement was reached in September 1940, and the first Packard-built engine, designated V-1650-1, ran in August 1941.[50]

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.[nb 7][30]


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. All Merlin engines were "right-hand tractor", i.e. propeller rotated to the right when viewed from rear, unless otherwise noted.

  • Merlin II or III
1,030 hp (775 kW) at 3,000 rpm at 5,500 ft (1,680 m); Merlin III fitted with "universal" propeller shaft able to mount either de Havilland or Rotol propellers,[51]
1,310 hp (977 kW) at 3,000 rpm at Template:Convert with 100 octane fuel and increased (+12 lb) boost (Merlin III);[29] both used in Spitfire Mk.I and Hurricane Mk.I fighters, the Boulton Paul Defiant, and Fairey Battle.[52]
  • Merlin X
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.
  • Merlin XII
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.[51]
  • Merlin XX
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.
  • Merlin 32
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.[51]
  • Merlin 45
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.
  • Merlin 47
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.
  • Merlin 50.M
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 Template:Convert in diameter. Permitted boost was +18 lb instead of +16 lb as on a normal Merlin 50 engine. A "negative-g" carburettor was fitted.[53][54][55]
  • Merlin 61
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.
  • Merlin 66
1,720 hp (1,283 kW) at 5,750 ft (1,752 m) using +18 lb boost (1.22 atm); low-altitude version of Merlin 61. Fitted with a Bendix-Stromberg anti-g carburettor;[56] used in Spitfire L.F Mk VIII and L.F Mk IX.[54]
  • Merlin 76/77
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.
  • Merlin 130/131
2,070 hp (1,543 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 (2,053 mm Hg). The Merlin 131 had an additional idler gear in the reduction gear casing allowing "reverse" (left-hand tractor) rotation. The Merlin 130 was fitted in the starboard nacelle, Merlin 131 in the port nacelle on production Hornets.
  • Merlin 133/134
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 (1.22 atm).
  • Merlin 266
The prefix "2" indicates engines built by Packard, otherwise as Merlin 66, optimised for low-altitude operation. Fitted to the Spitfire Mk. XVI.[54]


Aircraft list

List from Lumsden[nb 8] Template:Multicol




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.[57]

A Spanish-built version of the Messerschmitt Bf 109 G-2, the 1954 Hispano Aviación HA-1112-M1L Buchon, was built with the Rolls-Royce Merlin 500/45 engine of Template:Convert driving a four-bladed propeller, in the Hispano Aviación factory in Seville – 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.[58]

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.[59] 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.[60]

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 Races[61] and the Thompson Trophy.

Alternative applications


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.[62]

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.[63]


The Merlin engine 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.[64][65]

Engines on display

Many aerospace museums possess examples of the Merlin that are on public display, they include the:

Specifications (Merlin 61)

File:RR Merlin labeled.jpg
Rolls-Royce Merlin with components labelled


See also

Related development

Related lists

See also



  1. 1.0 1.1 Gunston 1989, p. 137. The naming tradition was started by managing director, Claude Johnson, in 1915 with the Eagle, Hawk and Falcon engines.
  2. Pugh 2000, pp. 192–198
  3. Merlin Engines in Manchester Retrieved: 14 August 2009
  4. The Spitfire and Merlin Retrieved: 14 August 2009
  5. Rubbra 1990, p. 64.
  6. Lumsden 2003, p. 203.
  7. Mason 1991, p. 168.
  8. McKinstry 2007, p. 53.
  9. Lumsden 2003, p. 200.
  10. Rubbra 1990, p. 118.
  11. Rubbra 1990, pp. 64–117.
  12. Rubbra 1990, pp. 82–92.
  13. Bridgman 1998, pp. 280–281.
  14. Lovesey 1946, pp. 224–226.
  15. Price 1982, p. 51.
  16. Tanner 1981, A.P.1565E, Vol.1, Section II.
  17. Lovesey 1946, p. 218.
  18. 18.0 18.1 Lumsden 2003, p. 201.
  19. Hooker 1984, p. 45.
  20. Hooker 1984, pp. 46–50, 52, 235–247.
  21. Lumsden 2003, p. 206.
  22. Rubbra 1990, p. 71.
  23. Hooker 1984, p. 62.
  24. McKinstry 2007, p. 205.
  25. Smallwood 1996, p. 135.
  26. Lumsden 2003, p. 212
  27. Flight 1938, p. 528.
  28. Payton-Smith 1971, pp. 259–260.
  29. 29.0 29.1 Harvey-Bailey 1995, p. 155.
  30. 30.0 30.1 Gunston, p. 144.
  31. Air Ministry 1940.
  32. Fozard 1991, pp. 127, 165.
  33. Flight 1946, p. 93.
  34. McKinstry 2007, p. 356.
  35. Lovesey 1946, pp. 222–223.
  36. 36.0 36.1 Price 1982. p. 170.
  37. 37.0 37.1 Berger & Street 1994. p. 199.
  38. 100/150 grade fuel Retrieved: 21 May 2008
  39. Derby factory closure Retrieved: 24 August 2009
  40. Pugh 2000, pp. 196–197.
  41. Crewe factory history Retrieved: 24 August 2009
  42. Pugh 2000, p. 197.
  43. Pugh 2000, p. 198.
  44. 44.0 44.1 End of era for Rolls-Royce plant. Retrieved: 25 August 2009
  45. Hillington factory history Retrieved: 24 August 2009
  46. 46.0 46.1 Nicholls 1996, p. 103.
  47. Hooker 1984, pp. 58–59.
  48. Nicholls 1996, p. 105.
  49. Time Magazine (8 July 1940) – Business: Ford's Rolls-Royces. Retrieved: 26 August 2009
  50. Lumsden 2003, p. 202.
  51. 51.0 51.1 51.2 Robertson 1973, p. 144.
  52. Bridgman 1998, p. 281.
  53. Lumsden 2003, p. 210.
  54. 54.0 54.1 54.2 Robertson 1973, p. 145.
  55. Price 1982, p. 145.
  56. Air Ministry 1943, p. 6.
  57. Lumsden 2003, pp. 214–215.
  58. Lumsden 2003, p. 214.
  59. Wilson, Randy. It's a Heinkel: the Luftwaffe's workhorse Heinkel 111 bomber, The Dispatch. Volume 12, Number 4, Winter 1996. Retrieved: 6 September 2009
  60. Green & Swanborough 1994, p. 211.
  61. Cleveland Air Races Retrieved: 4 September 2009
  62. Pugh 2000, p. 254.
  63. Marine history. Retrieved: 21 August 2009
  64. Shuttleworth Collection - Hawker Sea Hurricane IB Retrieved: 14 August 2009
  65. Shuttleworth Veteran Aeroplane Society (SVAS) - Spitfire restoration Retrieved: 14 August 2009



  • Air Ministry. A.P 1509B/J.2-W Merlin II and III Aero Engines (June 1940). London: Air Ministry, 1940.
  • Air Ministry. A.P 1565B Spifire IIA and IIB Aeroplanes: Merlin XII Engine, Pilot's Notes (July 1940). London: Air Data Publications, 1972 (reprint). ISBN 0-85979-043-6.
  • Air Ministry. Pilot's Notes for Spitfire Mark F.VII – Merlin 64 or 71 engine; Mark F.VIII – Merlin 63,66 or 70 engine. Air Publication 1565G & H -P.N. London, UK: Air Ministry, December 1943.
  • Beckles, Gordon. Birth of a Spitfire: The Story of Beaverbook's Ministry and its First £10,000,000. London: Collins Clear-Type Press, 1941.
  • Berger, Monty and Street, Brian Jeffrey.Invasion Without Tears. Toronto, Canada: Random House, 1994 (1st ed) ISBN 0-394-22277-6.
  • Bridgman, L. Jane's fighting aircraft of World War II. London: Crescent, 1998. ISBN 0-517-67964-7
  • Gunston, Bill.World Encyclopedia of Aero Engines (3rd edition). Sparkford, Somerset, UK: Patrick Stephens Limited, 1995. ISBN 1-85260-509-X.
  • Fozard, John W.Sydney Camm and the Hurricane; Perspectives on the master fighter designer and his finest achievement. Shrewsbury, Shropshire, UK: Airlife, 1991. ISBN 1-85310-270-9.
  • Green, William and Swanborough, Gordon. The Complete Book of Fighters. New York: Smithmark Publishers Inc., 1994. ISBN 0-8317-3939-8.
  • Harvey-Bailey, A. The Merlin in Perspective - the combat years. Derby, England: Rolls-Royce Heritage Trust, 1983. ISBN 1-872922-06-6
  • Hooker, Stanley Not Much of an Engineer London: Airlife, 1984. ISBN 1-85310-285-7.
  • Lovesey, A C. "Development of the Rolls-Royce Merlin from 1939 to 1945." Aircraft Engineering and Aerospace Technology, Volume 18, Issue 7. London, MCB UP Ltd., July 1946. ISSN 0002-2667.
  • Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.
  • Mason, Francis K. Hawker Aircraft Since 1920 (3rd revised edition). London, UK: Putnam, 1991. ISBN 0-85177-839-9.
  • McKinstry, Leo. Spitfire - Portrait of a Legend. London: John Murray, 2007. ISBN 0-71956-874-9.
  • Nicholls, Robert. Trafford Park: the First Hundred Years. Phillimore & Co. Ltd., 1996. ISBN 1-86077-013-4.
  • Payton-Smith, D J. Oil: A Study of War-time Policy and Administration. London: Her Majesty's Stationary Office, 1971.
  • Price, Alfred. The Spitfire Story. London: Jane's Publishing Company Ltd., 1982. ISBN 0-86720-624-1.
  • Pugh, Peter. The Magic of a Name - The Rolls-Royce Story - The First 40 Years. Cambridge, England. Icon Books Ltd, 2000. ISBN 1-84046-151-9.
  • Robertson, Bruce. Spitfire: The Story of a Famous Fighter. Hemel Hempstead, Hertfordshire, UK: Model & Allied Publications Ltd., 1960. Third revised edition 1973. ISBN 0-900435-11-9.
  • Rubbra, A.A. Rolls-Royce piston aero engines: A designer remembers. Derby, England: Rolls-Royce Heritage Trust, 1990. ISBN 1-872922-00-7.
  • Smallwood, Hugh. Spitfire in Blue. London: Osprey Aerospace, 1996. ISBN 1-85532-615-9.
  • Tanner, John. The Spitfire V Manual (AP1565E reprint). London: Arms and Armour Press, 1981. ISBN 0-85368-420-0.
  • "Some Trends in engine design (article and images)." Flight No. 1563, Volume XXXIV, 8 December 1938.
  • "Rolls-Royce Merlin 130 Series (article and images)." Flight No. 1935, Volume XLIX, 24 January 1946.

Further reading

  • Gunston, Bill. Development of Piston Aero Engines. Cambridge: Patrick Stephens, 2006. ISBN 0-7509-4478-1
  • Henshaw, Alex. Sigh for a Merlin: Testing the Spitfire. London: Crecy, 1999 (2nd revised edition). ISBN 0-9475-5483-1.
  • Jackson, Robert. The Encyclopedia of Military Aircraft Bath, UK: Parragon Books, 2006. ISBN 1-40542-465-6.
  • Price, Alfred. Spitfire Mark I/II Aces 1939–41. London: Osprey Aerospace, 1996. ISBN 1-85532-627-2.

External links

Template:Commons category


cs:Rolls-Royce Merlin de:Rolls-Royce Merlin es:Rolls Royce Merlin fr:Rolls-Royce Merlin it:Rolls-Royce Merlin nl:Rolls-Royce Merlin ja:ロールス・ロイス マーリン no:Rolls-Royce Merlin pl:Rolls-Royce Merlin fi:Rolls-Royce Merlin sv:Rolls-Royce Merlin

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It uses material from the Wikipedia article "Rolls-Royce Merlin".

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