Rolls-Royce Merlin
Overview
 
The Rolls-Royce Merlin is a British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 liquid-cooled, V-12
V12 engine
A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft....

, piston
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

 aero engine
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...

, of 27-litre
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...

 (1,650 cu in
Cubic inch
The cubic inch is a unit of measurement for volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its 3 sides being one inch long....

) capacity
Engine displacement
Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...

. Rolls-Royce Limited
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....

 designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin
Merlin (bird)
The Merlin is a small species of falcon from the Northern Hemisphere. A bird of prey once known colloquially as a pigeon hawk in North America, the Merlin breeds in the northern Holarctic; some migrate to subtropical and northern tropical regions in winter.-European and North American...

following the company convention of naming its piston aero engines after birds of prey
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....

.

The PV-12 first ran in 1933 and, after several modifications, the first production variants were built in 1936.
Encyclopedia
The Rolls-Royce Merlin is a British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 liquid-cooled, V-12
V12 engine
A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft....

, piston
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

 aero engine
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...

, of 27-litre
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...

 (1,650 cu in
Cubic inch
The cubic inch is a unit of measurement for volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its 3 sides being one inch long....

) capacity
Engine displacement
Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...

. Rolls-Royce Limited
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....

 designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin
Merlin (bird)
The Merlin is a small species of falcon from the Northern Hemisphere. A bird of prey once known colloquially as a pigeon hawk in North America, the Merlin breeds in the northern Holarctic; some migrate to subtropical and northern tropical regions in winter.-European and North American...

following the company convention of naming its piston aero engines after birds of prey
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....

.

The PV-12 first ran in 1933 and, after several modifications, the first production variants were built in 1936. The first operational aircraft to enter service using the Merlin were the Fairey Battle
Fairey Battle
The Fairey Battle was a British single-engine light bomber built by the Fairey Aviation Company in the late 1930s for the Royal Air Force. The Battle was powered by the same Rolls-Royce Merlin piston engine that gave contemporary British fighters high performance; however, the Battle was weighed...

, Hawker Hurricane
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...

 and Supermarine Spitfire
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...

. More Merlins were made for the four-engined Avro Lancaster
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...

 heavy bomber than for any other aircraft; however, the engine is most closely associated with the Spitfire, starting with the Spitfire's maiden flight in 1936. A series of rapidly applied developments, brought about by wartime needs, markedly improved the engine's performance and durability.

Considered a British icon, 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
Derby
Derby , is a city and unitary authority in the East Midlands region of England. It lies upon the banks of the River Derwent and is located in the south of the ceremonial county of Derbyshire. In the 2001 census, the population of the city was 233,700, whilst that of the Derby Urban Area was 229,407...

, Crewe
Crewe
Crewe is a railway town within the unitary authority area of Cheshire East and the ceremonial county of Cheshire, England. According to the 2001 census the urban area had a population of 67,683...

 and Glasgow
Glasgow
Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...

, as well as by Ford of Britain
Ford of Britain
Ford of Britain is a British wholly owned subsidiary of Ford of Europe, a subsidiary of Ford Motor Company. Its business started in 1909 and has its registered office in Brentwood, Essex...

 at their Trafford Park factory
Ford Trafford Park Factory
The Ford Trafford Park assembly plant was a car assembly plant established by the UK subsidiary of the Ford Motor Company. The plant was located at a recently established Industrial park called Trafford Park, beside the Manchester Ship Canal, a short distance to the west of Manchester...

, near Manchester
Manchester
Manchester is a city and metropolitan borough in Greater Manchester, England. According to the Office for National Statistics, the 2010 mid-year population estimate for Manchester was 498,800. Manchester lies within one of the UK's largest metropolitan areas, the metropolitan county of Greater...

. The Packard V-1650
Packard V-1650
The Packard V-1650 was a liquid cooled 27 litre 60° V12 piston aircraft engine variant of the Rolls-Royce Merlin produced under licence by the Packard Motor Car Company...

 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 airliner
Airliner
An airliner is a large fixed-wing aircraft for transporting passengers and cargo. Such aircraft are operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an aircraft intended for carrying multiple passengers in commercial...

s and military transport aircraft
Military transport aircraft
Military transport aircraft are typically fixed and rotary wing cargo aircraft which are used to deliver troops, weapons and other military equipment by a variety of methods to any area of military operations around the surface of the planet, usually outside of the commercial flight routes in...

.

In military use the Merlin was superseded by its larger capacity stablemate, the Rolls-Royce Griffon
Rolls-Royce Griffon
The Rolls-Royce Griffon is a British 37-litre capacity, 60-degree V-12, liquid-cooled aero engine designed and built by Rolls-Royce Limited...

. Merlin engines remain in Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 service today with the Battle of Britain Memorial Flight
Battle of Britain Memorial Flight
The Battle of Britain Memorial Flight is a Royal Air Force flight which provides an aerial display group comprising an Avro Lancaster, a Supermarine Spitfire and a Hawker Hurricane...

, and power many restored aircraft in private ownership worldwide.

Origin

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
Rolls-Royce Kestrel
|-See also:-Bibliography:* Erfurth, Helmut. Junkers Ju 87 . Bonn, Germany: Bernard & Graefe Verlag, 2004. ISBN 1-85780-186-5....

 that had been used with great success in a number of 1930s aircraft. Consequently, work was started on a new 1,100-horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

 (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
Hawker Hart
The Hawker Hart was a British two-seater biplane light bomber of the Royal Air Force , which had a prominent role during the RAF's inter-war period. The Hart was designed during the 1920s by Sydney Camm and built by Hawker Aircraft...

 biplane (serial number
United Kingdom military aircraft serials
In the United Kingdom to identify individual aircraft, all military aircraft are allocated and display a unique serial number. A unified serial number system, maintained by the Air Ministry , and its successor the Ministry of Defence , is used for aircraft operated by the Royal Air Force , Fleet...

 K3036) on 21 February 1935. The engine originally used the evaporative cooling system then in vogue. This proved unreliable and when supplies of ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...

 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.

In 1935, the Air Ministry
Air Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...

 issued a specification, F10/35, for new fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

 with a minimum airspeed of 310 miles per hour (500 km/h). Fortunately, two designs had been developed: the Supermarine Spitfire
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...

 and the Hawker Hurricane
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...

; the latter designed in response to another specification, F36/34. 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
Merlin (bird)
The Merlin is a small species of falcon from the Northern Hemisphere. A bird of prey once known colloquially as a pigeon hawk in North America, the Merlin breeds in the northern Holarctic; some migrate to subtropical and northern tropical regions in winter.-European and North American...

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
Rolls-Royce Peregrine
|-See also:-Bibliography:* Bowyer, Michael J.F. Interceptor Fighters for the Royal Air Force, 1935-45. Wellingborough, Northamptonshire, UK: Patrick Stephens Ltd., 1984. ISBN 0-85059-726-9....

 was an updated, supercharged
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...

 development of their V-12 Kestrel design, while the 1,700-horsepower (1,300 kW) 42-litre (2,560 cu in) Rolls-Royce Vulture
Rolls-Royce Vulture
|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...

 used four Kestrel-sized cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...

s fitted to a single crankcase
Crankcase
In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

 and driving a common crankshaft, forming an X-24 cylinder layout. This was to be used in larger aircraft such as the Avro Manchester
Avro Manchester
|-See also:-References:NotesCitationsBibliography* Buttler, Tony. British Secret Projects: Fighters and Bombers 1935–1950. Hickley, UK: Midland Publishing, 2004. ISBN 978-1857801798....

.

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
Westland Whirlwind (fixed wing)
The Westland Whirlwind was a British twin-engined heavy fighter developed by Westland Aircraft. It was the Royal Air Force's first single-seat, twin-engined, cannon-armed fighter, and a contemporary of the Supermarine Spitfire and Hawker Hurricane. It was one of the fastest aircraft when it flew in...

 and the Gloster F9/37. The Vulture was fitted to the Hawker Tornado
Hawker Tornado
-See also:-Bibliography:* Darling, Kev. Hawker Typhoon, Tempest and Sea Fury. Ramsgate, Marlborough, Wiltshire, UK: The Crowood Press Ltd., 2003. ISBN 1-86126-620-0....

 and Avro Manchester
Avro Manchester
|-See also:-References:NotesCitationsBibliography* Buttler, Tony. British Secret Projects: Fighters and Bombers 1935–1950. Hickley, UK: Midland Publishing, 2004. ISBN 978-1857801798....

, but proved unreliable in service. 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
Rolls-Royce Griffon
The Rolls-Royce Griffon is a British 37-litre capacity, 60-degree V-12, liquid-cooled aero engine designed and built by Rolls-Royce Limited...

. The Griffon incorporated several design improvements and ultimately superseded the Merlin.

Development

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. Early production Merlins were also unreliable: Common problems were cylinder head cracking, coolant leaks, and excessive wear to the camshafts and crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 main bearing
Main bearing
In a piston engine, the main bearings are the bearings on which the crankshaft rotates, usually plain or journal bearings.All engines have a minimum of two main bearings, one at each end of the crankshaft, and they may have as many as one more than the number of crank pins...

s.

Early engines

The prototype and developmental engine types were the:
  • PV-12
The initial design using an evaporative cooling system. Two built, passed bench
Dynamometer
A dynamometer or "dyno" for short, is a device for measuring force, moment of force , or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed .A dynamometer can also be used to determine...

 Type Testing in July 1934, generating 740 horsepower (552 kW) at 12000 feet (3,657.6 m) equivalent. First flown 21 February 1935.
  • Merlin B
Two built, ethylene glycol liquid cooling system introduced. "Ramp" cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...

s (inlet valves were at a 45-degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

 angle to the cylinder). Passed Type Testing February 1935, generating 950 horsepower (708 kW) at 11000 feet (3,352.8 m) equivalent.
  • Merlin C
Development of Merlin B; Crankcase
Crankcase
In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

 and cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...

s became three separate castings with bolt-on cylinder heads. First flight in Hawker Horsley
Hawker Horsley
|-See also:-Bibliography:* Jarrett, Philip. "By Day and By Night: Hawker Horsley part 1". Aeroplane Monthly, Volume 21 No 10, Issue 246, October 1993. pp. 32–40....

 21 December 1935, 950 horsepower (708 kW) at 11000 feet (3,352.8 m).
  • Merlin E
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.

  • Merlin F (Merlin I)
Similar to C and E. First flight in Horsley 16 July 1936. 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
Fairey Battle
The Fairey Battle was a British single-engine light bomber built by the Fairey Aviation Company in the late 1930s for the Royal Air Force. The Battle was powered by the same Rolls-Royce Merlin piston engine that gave contemporary British fighters high performance; however, the Battle was weighed...

 was the first production aircraft to be powered by the Merlin I and first flew on 10 March 1936.
  • Merlin G (Merlin II)
Replaced "ramp" cylinder heads with parallel pattern heads (valves parallel to the cylinder) scaled up from the Kestrel engine. 400 Hour flight endurance tests caried out at RAE
Royal Aircraft Establishment
The Royal Aircraft Establishment , was a British research establishment, known by several different names during its history, that eventually came under the aegis of the UK Ministry of Defence , before finally losing its identity in mergers with other institutions.The first site was at Farnborough...

 July 1937; Acceptance test 22 September 1937. It was first widely delivered as the 1,030-horsepower (770 kW) Merlin II in 1938, and production was quickly stepped up.

Production engines

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, allowing either de Havilland
De Havilland Propellers
de Havilland Propellers was established in 1935, as a division of the de Havilland Aircraft company when that company acquired a license from the Hamilton Standard company of America for the manufacture of variable pitch propellers...

 or Rotol
Dowty Rotol
Dowty Rotol is a British engineering company based in Cheltenham specialised in the manufacture of propellers and propeller components. It is owned by General Electric, forming part of its GE Aviation Systems division.-History:...

 manufactured propellers to be used.

The next major version was the XX which ran on 100 octane
Octane rating
Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

 fuel. This allowed higher manifold pressures
Manifold vacuum
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere....

, which were achieved by increasing the boost from the centrifugal type supercharger
Centrifugal type supercharger
The centrifugal-type supercharger is an engine-driven compressor used to increase the power output of an internal-combustion engine by increasing the amount of available oxygen by compressing air that is entering the engine...

. The Merlin XX incorporated the two-speed superchargers designed by Rolls-Royce, resulting in increased power at higher altitudes than previous versions. Another improvement, allowing 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
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...

, and reduced the oil leaks that had been a problem with the early Merlin I, II and III series.

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 (1,540 kW) in the Merlin 130/131 versions specifically designed for the de Havilland Hornet
De Havilland Hornet
The de Havilland DH.103 Hornet was a piston engine fighter that further exploited the wooden construction techniques pioneered by de Havilland's classic Mosquito. Entering service at the end of the Second World War, the Hornet equipped postwar RAF Fighter Command day fighter units in the UK and was...

. Ultimately, during tests conducted by Rolls-Royce at Derby
Derby
Derby , is a city and unitary authority in the East Midlands region of England. It lies upon the banks of the River Derwent and is located in the south of the ceremonial county of Derbyshire. In the 2001 census, the population of the city was 233,700, whilst that of the Derby Urban Area was 229,407...

, Merlin 130 series engines generated over 2,600 horsepower (1,940 kW).

Basic component overview (Merlin 61)

From Jane's:
Cylinders
Twelve cylinders consisting of high-carbon steel liners set in two, two-piece cylinder blocks of cast "R.R.50
Hiduminium
The Hiduminium or R.R. alloys are a series of high-strength, high-temperature aluminium alloys, developed for aircraft use by Rolls-Royce before World War II. They were manufactured and later developed by High Duty Alloys Ltd....

" aluminium alloy
Aluminium alloy
Aluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories...

 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
Phosphor bronze
Phosphor bronze is an alloy of copper with 3.5 to 10% of tin and a significant phosphorus content of up to 1%. The phosphorus is added as deoxidizing agent during melting....

 exhaust valve guides, and renewable "Silchrome" steel-alloy valve seats. Two diametrically opposed spark plug
Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...

s protrude into each combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

.

Pistons
Machined from "R.R.59
Hiduminium
The Hiduminium or R.R. alloys are a series of high-strength, high-temperature aluminium alloys, developed for aircraft use by Rolls-Royce before World War II. They were manufactured and later developed by High Duty Alloys Ltd....

" alloy forging
Forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...

s. Fully floating hollow gudgeon pins of hardened nickel-chrome steel. Three compression and one oil-control ring
Piston ring
A piston ring is a split ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.The three main functions of piston rings in reciprocating engines are:...

 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
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

. 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.

Crankshaft
One-piece, machined from a nitrogen-hardened nickel-chrome molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...

 steel forging. Statically and dynamically balanced
Engine balance
Engine balance is the design, construction and tuning of an engine to run smoothly. Improving engine balance reduces vibration and other stresses and can improve the overall performance, efficiency, cost of ownership and reliability of the engine, as well as reducing the stress on other machinery...

. Seven main bearings and six throws.

Crankcase
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
Propeller Speed Reduction Unit
A Propeller Speed Reduction Unit is a gearbox or a belt and pulley device used to reduce the output revolutions per minute from the higher input rpm of the powerplant...

. The lower half forms an oil sump and carries the oil pumps and filters.

Wheelcase
Aluminium casting fitted to rear of crankcase. Houses drives to the camshafts, magnetos
Magneto (electrical)
A magneto is an electrical generator that uses permanent magnets to produce alternating current.Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-powered internal combustion engines to provide power to the spark plugs...

, coolant and oil pumps, supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...

, hand and electric starters, and the electric generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...

.

Valve gear
Two inlet and two exhaust poppet valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...

s of "K.E.965" steel per cylinder. Both the inlet and exhaust valves have hardened "stellite
Stellite
Stellite alloy is a range of cobalt-chromium alloys designed for wear resistance. It may also contain tungsten or molybdenum and a small but important amount of carbon...

d" ends; while the exhaust valves also have sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

-cooled stems, and heads protected with a "Brightray
Brightray
Brightray is a nickel-chromium alloy that is noted for its resistance to erosion by gas flow at high temperatures. It was used for hard-facing the exhaust valve heads and seats of petrol engines, particularly aircraft engines from the 1930s onwards...

" (nickel-chromium) coating. Each valve is kept closed by a pair of concentric coil-springs
Coil spring
A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...

. A single, seven-bearing camshaft, located on the top of each cylinder head operates 24 individual steel rockers
Rocker arm
Generally referred to within the internal combustion engine of automotive, marine, motorcycle and reciprocating aviation engines, the rocker arm is a reciprocating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it...

; 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 inlet valves.

Technical improvements

Most of the Merlin's technical improvements resulted from more efficient superchargers
Centrifugal type supercharger
The centrifugal-type supercharger is an engine-driven compressor used to increase the power output of an internal-combustion engine by increasing the amount of available oxygen by compressing air that is entering the engine...

, designed by Stanley Hooker
Stanley Hooker
Sir Stanley George Hooker was a jet engine engineer, first at Rolls-Royce where he worked on the earliest designs such as the Welland and Derwent, and later at Bristol Aero Engines where he helped bring the troubled Proteus and Olympus to market, and then designed the famous Pegasus.Stanley George...

, and the introduction of aviation spirits with increased octane rating
Octane rating
Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

s. Numerous detail changes were made internally and externally to the engine to withstand increased power ratings and to incorporate advances in engineering practices.
Ejector exhausts


The Merlin consumed an enormous volume of air at full power (equivalent to the volume of a single-decker bus
Single-decker bus
A single-decker bus or single-decker is a bus that has a single deck for passengers. Normally the use of the term single-decker refers to a standard two-axled rigid bus, in direct contrast to the use of the term double-decker bus, which is essentially a single decked bus with an extra deck and...

 per minute), and with the exhaust gases exiting at 1,300 mph (2,100 km/h) it was realised that useful thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

 could be gained simply by angling the gases backwards instead of venting sideways.

During tests, 70 pounds-force
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...

 (310 N; 32 kgf
Kilogram-force
A kilogram-force , or kilopond , is a gravitational metric unit of force. It is equal to the magnitude of the force exerted by one kilogram of mass in a gravitational field...

) thrust at 300 miles per hour (480 km/h), or roughly 70 horsepower (52 kW) was obtained which increased the level maximum speed of the Spitfire by 10 mph (16 km/h) to 360 mph (580 km/h). The first versions of the ejector exhausts featured round outlets, while subsequent versions of the system used "fishtail" style outlets which marginally increased thrust and reduced exhaust glare for night flying.

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 altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

s, 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
Lapse rate
The lapse rate is defined as the rate of decrease with height for an atmospheric variable. The variable involved is temperature unless specified otherwise. The terminology arises from the word lapse in the sense of a decrease or decline; thus, the lapse rate is the rate of decrease with height and...

. Ejector exhausts were also fitted to other Merlin-powered aircraft.
Supercharger

Central to the success of the Merlin was the supercharger. A.C. Lovesey
Cyril Lovesey
Alfred Cyril Lovesey CBE, AFRAeS, was an English engineer who was a key figure in the development of the Rolls-Royce Merlin aero engine.-Early life:...

, 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:
  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 ... 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."


As the Merlin evolved so too did the supercharger; the latter fitting into three broad categories:
  1. Single-stage, single-speed gearbox: Merlin I to III, XII, 30, 40, and 50 series (1937–1942).
  2. Single-stage, two-speed gearbox: experimental Merlin X (1938), production Merlin XX (1940–1945).
  3. Two-stage, two-speed gearbox with intercooler
    Intercooler
    An intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...

    : mainly Merlin 60, 70, and 80 series (1942–1946).


The Merlin supercharger was originally designed to allow the engine to generate maximum power at an altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

 of about 16,000 feet (5,000 m). In 1938 Stanley Hooker, an Oxford
University of Oxford
The University of Oxford is a university located in Oxford, United Kingdom. It is the second-oldest surviving university in the world and the oldest in the English-speaking world. Although its exact date of foundation is unclear, there is evidence of teaching as far back as 1096...

 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 subsequently designed a new air intake duct with improved flow characteristics which increased maximum power at a higher altitude of over 19,000 feet (5,800 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.

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. The later Merlin XX incorporated the two-speed drive as well as several improvements that enabled the production rate of Merlins to be increased. 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
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

 (1.66 atm
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...

) boost.

In 1940, after receiving a request for a high-rated Merlin for use as an alternative engine to the turbocharged Hercules VIII
Bristol Hercules
|-See also:-Bibliography:*Gunston, B. Classic World War II Aircraft Cutaways. Osprey. ISBN 1-85532-526-8*Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...

 used in the prototype high-altitude Vickers Wellington V
Vickers Wellington
The Vickers Wellington was a British twin-engine, long range medium bomber designed in the mid-1930s at Brooklands in Weybridge, Surrey, by Vickers-Armstrongs' Chief Designer, R. K. Pierson. It was widely used as a night bomber in the early years of the Second World War, before being displaced as a...

 bomber, Rolls-Royce started experiments on the design of a two-stage supercharger and an engine fitted with this was bench-tested in April 1941, eventually becoming the Merlin 60. The basic design used a modified Vulture supercharger for the first stage while a Merlin 46 supercharger was used for the second. A liquid-cooled intercooler
Intercooler
An intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...

 on top of the supercharger casing was used to prevent the compressed air/fuel mixture from becoming too hot. Also considered was an exhaust-driven turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...

 but, although a lower fuel consumption was an advantage the added weight and the need to add extra ducting for the exhaust flow and waste-gates, meant that this option was rejected in favour of the two-stage supercharger. 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.

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.

While the design of the two-stage supercharger forged ahead, Rolls-Royce also continued to develop the single-stage supercharger, resulting in 1942 in the development of a smaller "cropped" impeller for the Merlin 45M and 55M; both of these engines developed greater power at low altitudes. 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
Wingspan
The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...

, the less-than-perfect condition of the used airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...

s and the cropped supercharger impeller.
Carburettor developments


The use of carburettors
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....

 was calculated to give a higher specific power
Power density
Power density is the amount of power per unit volume....

 output, due to the lower temperature, hence greater density, of the fuel/air mixture compared to injected systems. However, the Merlin's float controlled carburettor meant that both Spitfires
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...

 and Hurricanes
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...

 were unable to pitch nose down into a steep dive. The contemporary Bf 109E
Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...

, 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-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...

 (g). RAF fighter pilots soon learned to "half-roll" their aircraft before diving to pursue their opponents. "Miss Shilling's orifice
Miss Shilling's orifice
Miss Shilling's Orifice was a very simple technical device made to counter engine cut-out in early Spitfire and Hurricane fighter aeroplanes during the Battle of Britain...

", 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.

Further improvements were introduced throughout the Merlin range: 1943 saw the introduction of a Bendix-Stromberg
Bendix Corporation
The Bendix Corporation was an American manufacturing and engineering company which during various times in its 60 year existence made brake systems, aeronautical hydraulics, avionics, aircraft and automobile fuel control systems, radios, televisions and computers, and which licensed its name for...

 pressure carburettor
Pressure carburetor
A pressure carburetor is a type of fuel metering system manufactured by the Bendix Corporation for piston aircraft engines, starting in the 1940s. It is recognized as an early type of throttle-body fuel injection and was developed to prevent fuel starvation during inverted flight.-Concept:Most...

 that injected fuel at 5 pounds per square inch
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

 (34 kPa; 0.34 bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

) 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.
Improved fuels

At the start of the war the Merlin I, II and III ran on the then standard 87 octane aviation spirit
Avgas
Avgas is an aviation fuel used to power piston-engine aircraft. Avgas is distinguished from mogas , which is the everyday gasoline used in cars and some non-commercial light aircraft...

 and could supply just over 1,000 horsepower (750 kW) from its 27-litre (1,650-cu in
Cubic inch
The cubic inch is a unit of measurement for volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its 3 sides being one inch long....

) displacement: the maximum boost pressure at which the engine could be run using 87 octane fuel was +6 pounds per square inch (141 kPa; 1.44 atm
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...

). 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).

From late 1939, 100 octane fuel became available from the U.S., West Indies, Persia and domestically. Merlin IIs and IIIs were adapted to run on the new fuel, using an increased boost pressure of +12 pounds per square inch (183 kPa; 1.85 atm). Small modifications were made to the engines which were now capable of generating 1,310 horsepower (977 kW) at 9000 ft (2,743.2 m) while running at 3,000 revolutions per minute. 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 (183 kPa; 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. Later versions of the Merlin ran only on 100 octane fuel and the five-minute combat limitation was raised to +18 pounds per square inch (224 kPa; 2.3 atm).

In late 1943 trials were run of a new "100/150" grade (150 octane) fuel, recognised by its bright-green colour and "awful smell". Initial tests were conducted using 6.5 cc of tetraethyllead (T.E.L.) for every one imperial gallon of 100 octane fuel (or 1.43 cc/L or 0.18 U.S. fl oz/U.S. gal), but this mixture resulted in a build-up of lead in the combustion chambers, causing excessive fouling of the spark plug
Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...

s. Better results were achieved by adding 2.5% mono methyl aniline
Aniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...

 (M.M.A.) to 100 octane fuel. The new fuel allowed the five-minute boost rating of the Merlin 66 to be raised to +25 pounds per square inch (272 kPa; 2.7 atm).

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 bomb
V-1 flying bomb
The V-1 flying bomb, also known as the Buzz Bomb or Doodlebug, was an early pulse-jet-powered predecessor of the cruise missile....

s coming in at low altitudes, as well as by other fighters flown by the ADGB
Air Defence of Great Britain
The Air Defence of Great Britain was a RAF command comprising substantial Army and RAF elements responsible for the air defence of the British Isles...

, but continued problems with backfires
Back-fire
A Back-fire or backfire is an explosion produced by a running internal combustion engine that occurs in the air intake or exhaust system rather than inside the combustion chamber. The same term is used when unburned fuel or hydrocarbons are ignited somewhere in the exhaust system. A visible flame...

 were not remedied until August.

In early February 1945, Spitfires of the 2 TAF also began using 100/150 grade fuel. Monty Berger, Senior Intelligence Officer of 126 (RCAF) Spitfire Wing, 2 TAF, noted that there were still problems being experienced with the new fuel on his wing, leading to several fatal accidents. Pilots were relieved when the return to 130 grade was authorised by April 1945.

Production

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
Air Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...

 and local authority officials. Hives was an advocate of shadow factories
British shadow factories
British shadow factories were a plan developed by the British Government to implement additional manufacturing capacity for the British aircraft industry, in the build up to World War II...

, 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
Industrial action
Industrial action or job action refers collectively to any measure taken by trade unions or other organised labour meant to reduce productivity in a workplace. Quite often it is used and interpreted as a euphemism for strike, but the scope is much wider...

. 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.

Derby

The existing Rolls-Royce facilities at Osmaston, Derby
Osmaston, Derby
Osmaston is a suburb of the city of Derby, England. It is situated about 4 km south of the city centre, it is written in the Domesday Book as Osmundestune. In 1307 the manor of Osmaston was granted to Robert Holland. It was the location of Osmaston Hall the residence of the Wilmots Baronets...

 were not suitable for large-scale engine production although the floor space
Area
Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...

 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
Hucknall Airfield
Formerly RAF Hucknall, Hucknall Airfield is located north northwest of Nottingham, Nottinghamshire, England.Hucknall has been in continuous use as an airfield since 1916. Formerly RAF Hucknall, it featured in the film The One That Got Away...

. The original factory closed in March 2008, but Rolls-Royce plc
Rolls-Royce plc
Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...

 still maintains a large presence in Derby.

Crewe

To meet the increasing demand for Merlin engines, Rolls-Royce started building work on a new factory
Bentley Crewe
Bentley Crewe serves as the headquarters, design and manufacturing centre of Bentley Motors Limited, located on the outskirts of Crewe, Cheshire, England.-History:...

 at Crewe
Crewe
Crewe is a railway town within the unitary authority area of Cheshire East and the ceremonial county of Cheshire, England. According to the 2001 census the urban area had a population of 67,683...

 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
Subcontractor
A subcontractor is an individual or in many cases a business that signs a contract to perform part or all of the obligations of another's contract....

 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".

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
Strike action
Strike action, also called labour strike, on strike, greve , or simply strike, is a work stoppage caused by the mass refusal of employees to work. A strike usually takes place in response to employee grievances. Strikes became important during the industrial revolution, when mass labour became...

 took place when women replaced men on capstan lathes
Turret lathe
The turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable...

, the workers' union
Trade union
A trade union, trades union or labor union is an organization of workers that have banded together to achieve common goals such as better working conditions. The trade union, through its leadership, bargains with the employer on behalf of union members and negotiates labour contracts with...

 insisting this was a skilled labour job; however, the men returned to work after 10 days. Post-war the factory was used for the production of Bentley
Bentley
Bentley Motors Limited is a British manufacturer of automobiles founded on 18 January 1919 by Walter Owen Bentley known as W.O. Bentley or just "W O". Bentley had been previously known for his range of rotary aero-engines in World War I, the most famous being the Bentley BR1 as used in later...

 motor cars, and in 1998 Volkswagen AG bought both the marque and the factory. Today it is known as Bentley Crewe.

Glasgow

Hives further recommended that a factory be built near Glasgow
Glasgow
Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...

 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
Hillington, Glasgow
Hillington is a residential suburb and an industrial estate on the southwestern edge of the Scottish city of Glasgow. Whilst the residential area is wholly within Glasgow, the greater part of the industrial estate falls under the jurisdiction of neighbouring Renfrew, although for business...

 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.

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 subcontractor
Subcontractor
A subcontractor is an individual or in many cases a business that signs a contract to perform part or all of the obligations of another's contract....

s, it produced almost all the Merlin's components itself. 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. In total 23,675 engines were produced. Worker absenteeism
Absenteeism
Absenteeism is a habitual pattern of absence from a duty or obligation. Traditionally, absenteeism has been viewed as an indicator of poor individual performance, as well as a breach of an implicit contract between employee and employer; it was seen as a management problem, and framed in economic...

 became a problem after some months due to the physical and mental effects of wartime conditions such as the frequent occupation of air-raid shelter
Air-raid shelter
Air-raid shelters, also known as bomb shelters, are structures for the protection of the civil population as well as military personnel against enemy attacks from the air...

s. It was agreed to cut the punishing working hours slightly to 82 hours a week, with one half-Sunday per month awarded as holiday. Record production is reported to have been 100 engines in one day.

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
Rolls-Royce Avon
|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:**** a 1955 Flight article on the development of the Avon...

 turbojet and others, the factory was closed in 2005.

Manchester

Early in 1940 Ford of Britain
Ford of Britain
Ford of Britain is a British wholly owned subsidiary of Ford of Europe, a subsidiary of Ford Motor Company. Its business started in 1909 and has its registered office in Brentwood, Essex...

 was approached by Herbert Austin
Herbert Austin
Herbert 'Pa' Austin, 1st Baron Austin KBE was an English automobile designer and builder who founded the Austin Motor Company.-Background and early life:...

, who was in charge of the shadow factory plan, about the possibility of converting an abandoned factory in Trafford Park
Trafford Park
Trafford Park is an area of the Metropolitan Borough of Trafford, in Greater Manchester, England. Located opposite Salford Quays, on the southern side of the Manchester Ship Canal, it is west-southwest of Manchester city centre, and north of Stretford. Until the late 19th century it was the...

 into an aircraft engine production unit. Construction of the new factory was started in May 1940 on a 118 acres (47.8 ha) site. During this time Ford engineers went on a fact finding mission to Derby, where their chief engineer commented to Sir Stanley Hooker that the manufacturing tolerances used by Rolls-Royce were far too wide for them. As a consequence over a year was taken up re-drafting 20,000 drawings to Ford tolerance levels.

Ford's factory, which was completed in May 1941, was built in two distinct sections to limit potential bomb damage. At first, the factory had difficulty in attracting suitable labour, such that 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 after the factory's completion, and the production rate was 200 Merlins per week by 1943. Ford’s investment in machinery and the redesign resulted in the 10,000 man-hours needed to produce a Merlin dropping to 2,727 man-hours three years later, while unit cost fell from £6,540 in June 1941 to £1,180 by the war’s end. 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. The percentage of engines rejected by the Air Ministry was zero. Not one engine of the 30,400 produced was rejected ...". Some 17,316 people worked at the Trafford Park 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.

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
Henry Ford
Henry Ford was an American industrialist, the founder of the Ford Motor Company, and sponsor of the development of the assembly line technique of mass production. His introduction of the Model T automobile revolutionized transportation and American industry...

 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 $
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....

130,000,000 Merlin order. Agreement was reached in September 1940, and the first Packard-built engine, designated V-1650-1, ran in August 1941.

Variants

This is a list of representative Merlin variants, describing some of the mechanical changes made during development of the Merlin. 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. Power ratings quoted are usually maximum "military" power. All but the Merlin 131 and 134 engines were "right-hand tractor", i.e. the propeller rotated clockwise when viewed from the rear. In addition to the mark numbers, Merlin engines were allocated experimental numbers by the Ministry of Supply
Ministry of Supply
The Ministry of Supply was a department of the UK Government formed in 1939 to co-ordinate the supply of equipment to all three British armed forces, headed by the Minister of Supply. There was, however, a separate ministry responsible for aircraft production and the Admiralty retained...

 (MoS) - e.g.: RM 8SM for the Merlin 61 and some variants - while under development; these numbers are noted where possible.

Data from Bridgman (Jane's) unless otherwise noted:
  • Merlin II (RM 1S)
1,030 hp (775 kW) at 3,000 rpm at 5,500 ft (1,680 m) using + 6 psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

 boost (41 kPa gauge; or an absolute pressure of 144 kPa or 1.41 atm); used 100% glycol coolant. First production Merlin II delivered 10 August 1937. Merlin II used in the Boulton Paul Defiant
Boulton Paul Defiant
The Boulton Paul Defiant was a British interceptor aircraft that served with the Royal Air Force early in the Second World War. The Defiant was designed and built by Boulton Paul Aircraft as a "turret fighter", without any forward-firing guns. It was a contemporary of the Royal Navy's Blackburn Roc...

, Hawker Hurricane Mk.I
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...

, Supermarine Spitfire Mk.I fighters, and Fairey Battle
Fairey Battle
The Fairey Battle was a British single-engine light bomber built by the Fairey Aviation Company in the late 1930s for the Royal Air Force. The Battle was powered by the same Rolls-Royce Merlin piston engine that gave contemporary British fighters high performance; however, the Battle was weighed...

 light bomber.
  • Merlin III (RM 1S)
Merlin III fitted with "universal" propeller shaft able to mount either de Havilland
De Havilland Propellers
de Havilland Propellers was established in 1935, as a division of the de Havilland Aircraft company when that company acquired a license from the Hamilton Standard company of America for the manufacture of variable pitch propellers...

 or Rotol
Dowty Rotol
Dowty Rotol is a British engineering company based in Cheltenham specialised in the manufacture of propellers and propeller components. It is owned by General Electric, forming part of its GE Aviation Systems division.-History:...

 propellers,. From late 1939, using 100 octane fuel and +12 psi boost (83 kPa gauge; or an absolute pressure of 184 kPa or 1.82 atm), the Merlin III developed 1,310 hp (977 kW) at 3,000 rpm at 9000 ft (2,743.2 m); using 87 octane fuel the power ratings were the same as the Merlin II. Used in the Defiant, Hurricane Mk.I, Spitfire Mk.I fighters, and Battle light bomber. First production Merlin III delivered 1 July 1938.
  • Merlin X (RM 1SM)
1,130 hp (840 kW) at 3,000 rpm at 5,250 ft (1,525 m); maximum boost pressure +10 psi; this was the first production Merlin to use a two-speed supercharger; Used in Halifax Mk.I, Wellington Mk.II
Vickers Wellington
The Vickers Wellington was a British twin-engine, long range medium bomber designed in the mid-1930s at Brooklands in Weybridge, Surrey, by Vickers-Armstrongs' Chief Designer, R. K. Pierson. It was widely used as a night bomber in the early years of the Second World War, before being displaced as a...

, and Whitley Mk.V bombers. First production Merlin X, 5 December 1938.

  • Merlin XII (RM 3S)
1,150 hp (860 kW); fitted with Coffman engine starter
Coffman engine starter
The Coffman engine starter was a starting system used on many piston engines in aircraft and armored vehicles of the 1930s and 1940s. The Coffman system was one of the most common brands; another was the Breeze cartridge system, which was produced under Coffman patents...

; first version to use 70/30% water/glycol coolant rather than 100% glycol. Reinforced construction, able to use constant boost pressure of up to +12 psi using 100 octane fuel; Used in Spitfire Mk.II. First production Merlin XII, 2 September 1939.
  • Merlin XX (RM 3SM)
1,480 hp (1,105 kW) at 3,000 rpm at 6,000 ft (1,830 m); two-speed supercharger; boost pressure of up to +14 psi; Used in Hurricane Mk.II, Beaufighter Mk.II
Bristol Beaufighter
The Bristol Type 156 Beaufighter, often referred to as simply the Beau, was a British long-range heavy fighter modification of the Bristol Aeroplane Company's earlier Beaufort torpedo bomber design...

, s, Halifax Mk.II and Lancaster Mk.I
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...

 bombers, and in the Spitfire Mk.III prototypes (N3297 & W3237). First production Merlin XX, 4 July 1940.
  • Merlin 32 (RM 5M)
1,645 hp (1,230 kW) at 3,000 rpm at 2,500 ft (760 m); first "low altitude" version of Merlin with cropped supercharger impellers for increased power at lower altitudes; fitted with Coffman engine starter; used mainly in Fleet Air Arm
Fleet Air Arm
The Fleet Air Arm is the branch of the British Royal Navy responsible for the operation of naval aircraft. The Fleet Air Arm currently operates the AgustaWestland Merlin, Westland Sea King and Westland Lynx helicopters...

 aircraft, mainly the Fairey Barracuda Mk.II
Fairey Barracuda
The Fairey Barracuda was a British carrier-borne torpedo- and dive bomber used during the Second World War, the first of its type used by the Royal Navy's Fleet Air Arm to be fabricated entirely from metal. It was introduced as a replacement for the Fairey Swordfish and Fairey Albacore biplanes...

 torpedo bomber and Fairey Fulmar
Fairey Fulmar
The Fairey Fulmar was a British carrier-borne fighter aircraft that served with the Fleet Air Arm during the Second World War. A total of 600 were built by Fairey Aviation at its Stockport factory between January 1940 and December 1942...

 and Supermarine Seafire F. Mk.IIc
Supermarine Seafire
The Supermarine Seafire was a naval version of the Supermarine Spitfire specially adapted for operation from aircraft carriers. The name Seafire was arrived at by collapsing the longer name Sea Spitfire.-Origins of the Seafire:...

 fighters. Also Hurricane Mk.V and Spitfire P.R Mk.XIII. First production Merlin 32, 17 June 1942.
  • Merlin 45 (RM 5S)
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. Maximum boost pressure of +16 psi. First production Merlin 45, 13 January 1941.
  • Merlin 47 (RM 6S)
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. First production Merlin 47, 2 December 1941.
  • Merlin 50.M (RM 5S)
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 9.5 in (241.3 mm) in diameter. Permitted boost was +18 psi (125 kPa gauge; or an absolute pressure of 225 kPa or 2.2 atm) instead of +16 psi (110 kPa gauge; or an absolute pressure of 210 kPa or 2.08 atm) on a normal Merlin 50 engine. Merlin 50 series was first to use the Bendix-Stromberg "negative-g" carburettor.
  • Merlin 61 (RM 8SM)
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. First British production variant to incorporate two-piece cylinder blocks designed by Rolls-Royce for the Packard Merlin
Packard V-1650
The Packard V-1650 was a liquid cooled 27 litre 60° V12 piston aircraft engine variant of the Rolls-Royce Merlin produced under licence by the Packard Motor Car Company...

. First production Merlin 61, 2 March 1942.

  • Merlin 66 (RM 10SM)
1,720 hp (1,283 kW) at 5790 ft (1,764.8 m) using +18 psi boost (124 kPa gauge; or an absolute pressure of 225 kPa or 2.2 atm); low-altitude version of Merlin 61. Fitted with a Bendix-Stromberg anti-g carburettor; used in Spitfire L.F Mk.VIII and L.F Mk.IX.
  • Merlin 76/77 (RM 16SM)
1,233 hp (920 kW) at 35000 ft (10,668 m); Fitted with a two-speed, two-stage supercharger and a Bendix-Stromberg carburettor. Dedicated "high altitude" version used in the Westland Welkin
Westland Welkin
|-See also:-Bibliography:* Buttler, Tony. British Secret Projects: Fighters and Bombers 1935–1950. Hinckley, UK: Midland, 2004. ISBN 1-85780-179-2....

 high-altitude fighter and some later Spitfire and de Havilland Mosquito
De Havilland Mosquito
The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...

 variants. The odd-numbered mark drove a blower for pressurising
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...

 the cockpit.
  • Merlin 130/131
2,060 hp (1,536 kW); redesigned "slimline" versions for the de Havilland Hornet
De Havilland Hornet
The de Havilland DH.103 Hornet was a piston engine fighter that further exploited the wooden construction techniques pioneered by de Havilland's classic Mosquito. Entering service at the end of the Second World War, the Hornet equipped postwar RAF Fighter Command day fighter units in the UK and was...

. 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 psi (170 kPa gauge; or an absolute pressure of 270 kPa or 2.7 atm). On the Hornet the Merlin 130 was fitted in the starboard nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...

: the Merlin 131, fitted in the port nacelle, was converted to a "reverse" or left-hand tractor engine using an additional idler gear in the reduction gear casing
Propeller Speed Reduction Unit
A Propeller Speed Reduction Unit is a gearbox or a belt and pulley device used to reduce the output revolutions per minute from the higher input rpm of the powerplant...

.
  • Merlin 133/134
2,030 hp (1,514 kW); derated 130/131 variants used in Sea Hornet
De Havilland Hornet
The de Havilland DH.103 Hornet was a piston engine fighter that further exploited the wooden construction techniques pioneered by de Havilland's classic Mosquito. Entering service at the end of the Second World War, the Hornet equipped postwar RAF Fighter Command day fighter units in the UK and was...

 F. Mk. 20, N.F. Mk. 21 and P.R. Mk. 22. Maximum boost was lowered to +18 psi gauge (230 kPa or 2.2 atm absolute).
  • Merlin 266 (RM 10SM)
The prefix "2" indicates engines built by Packard
Packard
Packard was an American luxury-type automobile marque built by the Packard Motor Car Company of Detroit, Michigan, and later by the Studebaker-Packard Corporation of South Bend, Indiana...

, otherwise as Merlin 66, optimised for low-altitude operation. Fitted to the Spitfire Mk.XVI.
  • Merlin 620
1,175 hp (876 kW) continuous cruising using 2,650 rpm at +9 psi boost (62 kPa gauge; or an absolute pressure of 165 kPa or 1.6 atm); capable of emergency rating of 1,795 hp (1,338 kW) at 3,000 rpm using +20 psi boost (138 kPa gauge; or an absolute pressure of 241 kPa or 2.4 atm) ; civilian engine developed from Merlin 102; two-stage supercharger optimised for medium altitudes, and used an S.U. injection carburettor. "Annular" radiator installation development of that used on Avro Lincoln
Avro Lincoln
The Avro Type 694, better known as the Avro Lincoln, was a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were known initially as the Lancaster IV and V, but were renamed Lincoln I and II...

. The Merlin 620-621 series was designed to operate in the severe climatic conditions encountered on Canadian and long-range North Atlantic air routes. Used in Avro Tudor
Avro Tudor
Avro's Type 688 Tudor was a British piston-engined airliner based on their four-engine Lincoln bomber, itself a descendant of the famous Lancaster heavy bomber, and was Britain's first pressurised airliner...

, Avro York
Avro York
The Avro York was a British transport aircraft that was derived from the Second World War Lancaster heavy bomber, and used in both military and airliner roles between 1943 and 1964.-Design and development:...

, and the Canadair North Star
Canadair North Star
The Canadair North Star was a 1940s Canadian development of the Douglas C-54 / DC-4 aircraft. Instead of radial piston engines found on the Douglas design, Canadair employed Rolls-Royce Merlin engines in order to achieve a 35 mph faster cruising speed. The prototype flew on 15 July 1946 and...

.

Applications

In chronological order, the first operational aircraft powered by the Merlin to enter service were the Fairey Battle, Hawker Hurricane and Supermarine Spitfire. 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.

List from Lumsden 2003
  • Armstrong Whitworth Whitley
    Armstrong Whitworth Whitley
    The Armstrong Whitworth A.W.38 Whitley was one of three British twin-engine, front line medium bomber types in service with the Royal Air Force at the outbreak of the Second World War...

  • Avro Athena
    Avro Athena
    |-See also:-External links:*...

  • Avro Lancaster
    Avro Lancaster
    The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...

  • Avro Lancastrian
    Avro Lancastrian
    |-See also:-References:NotesBibliography* Franks, Richard A. The Avro Lancaster, Manchester and Lincoln: A Comprehensive Guide for the Modeller. London: SAM Publications, 2000. ISBN 0-9533465-3-6....

  • Avro Lincoln
    Avro Lincoln
    The Avro Type 694, better known as the Avro Lincoln, was a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were known initially as the Lancaster IV and V, but were renamed Lincoln I and II...

  • Avro Manchester III
    Avro Manchester
    |-See also:-References:NotesCitationsBibliography* Buttler, Tony. British Secret Projects: Fighters and Bombers 1935–1950. Hickley, UK: Midland Publishing, 2004. ISBN 978-1857801798....

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

  • Avro York
    Avro York
    The Avro York was a British transport aircraft that was derived from the Second World War Lancaster heavy bomber, and used in both military and airliner roles between 1943 and 1964.-Design and development:...

  • Boulton Paul Balliol and Sea Balliol
    Boulton Paul Balliol
    |-See also:-References:NotesBibliography* Donald, David, ed. The Encyclopedia of World Aircraft. London: Aerospace Publishing, 1997. ISBN 1-85605-375-X....

  • Boulton Paul Defiant
    Boulton Paul Defiant
    The Boulton Paul Defiant was a British interceptor aircraft that served with the Royal Air Force early in the Second World War. The Defiant was designed and built by Boulton Paul Aircraft as a "turret fighter", without any forward-firing guns. It was a contemporary of the Royal Navy's Blackburn Roc...

  • Bristol Beaufighter
    Bristol Beaufighter
    The Bristol Type 156 Beaufighter, often referred to as simply the Beau, was a British long-range heavy fighter modification of the Bristol Aeroplane Company's earlier Beaufort torpedo bomber design...

  • CAC CA-18 Mark 23 Mustang
    P-51 Mustang
    The North American Aviation P-51 Mustang was an American long-range, single-seat fighter and fighter-bomber used during World War II, the Korean War and in several other conflicts...

  • Canadair North Star
    Canadair North Star
    The Canadair North Star was a 1940s Canadian development of the Douglas C-54 / DC-4 aircraft. Instead of radial piston engines found on the Douglas design, Canadair employed Rolls-Royce Merlin engines in order to achieve a 35 mph faster cruising speed. The prototype flew on 15 July 1946 and...

  • CASA 2.111
    CASA 2.111
    -See also:-References:NotesBibliography* Cruz, Gonzalo Avila. "Homegrown 'Pedros': Spanish-Built Heinkel He 111s: Part One-Jumo Variants". Air Enthusiast, No. 90, November/December 2000. Stamford, UK:Key Publishing, pp. 48–53. ISSN 0143-5450....

  • Cierva Air Horse
    Cierva Air Horse
    -References:NotesReferences* Copies of entries in "The Complete Encyclopedia of World Aircraft", 1997. by D.Donald and "Helicopters and Autogyros of the World", 1958 by P.Lambermont. Hosted at www.aviastar.org. Accessed January 2008...


  • de Havilland Mosquito
    De Havilland Mosquito
    The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...

  • de Havilland Hornet
    De Havilland Hornet
    The de Havilland DH.103 Hornet was a piston engine fighter that further exploited the wooden construction techniques pioneered by de Havilland's classic Mosquito. Entering service at the end of the Second World War, the Hornet equipped postwar RAF Fighter Command day fighter units in the UK and was...

  • Fairey Barracuda
    Fairey Barracuda
    The Fairey Barracuda was a British carrier-borne torpedo- and dive bomber used during the Second World War, the first of its type used by the Royal Navy's Fleet Air Arm to be fabricated entirely from metal. It was introduced as a replacement for the Fairey Swordfish and Fairey Albacore biplanes...

  • Fairey Battle
    Fairey Battle
    The Fairey Battle was a British single-engine light bomber built by the Fairey Aviation Company in the late 1930s for the Royal Air Force. The Battle was powered by the same Rolls-Royce Merlin piston engine that gave contemporary British fighters high performance; however, the Battle was weighed...

  • Fairey Fulmar
    Fairey Fulmar
    The Fairey Fulmar was a British carrier-borne fighter aircraft that served with the Fleet Air Arm during the Second World War. A total of 600 were built by Fairey Aviation at its Stockport factory between January 1940 and December 1942...

  • Fairey P.4/34
    Fairey P.4/34
    -See also:-Bibliography:* Mason, Francis K. The British Bomber since 1914. London: Putnam Aeronautical Books, 1994. ISBN 0-85177-861-5.* Taylor, H.A. Fairey Aircraft since 1915. London: Putnam, 1974. ISBN 0-370-00065-x.-External links:**...

  • Fiat G.59
  • Handley Page Halifax
    Handley Page Halifax
    The Handley Page Halifax was one of the British front-line, four-engined heavy bombers of the Royal Air Force during the Second World War. A contemporary of the famous Avro Lancaster, the Halifax remained in service until the end of the war, performing a variety of duties in addition to bombing...

  • Handley Page Halton
  • Hawker Hart
    Hawker Hart
    The Hawker Hart was a British two-seater biplane light bomber of the Royal Air Force , which had a prominent role during the RAF's inter-war period. The Hart was designed during the 1920s by Sydney Camm and built by Hawker Aircraft...

  • Hawker Henley
    Hawker Henley
    -See also:-References:NotesBibliography* Cooper, H.J.,O.G. Thetford and C.B. Maycock. Aircraft of the Fighting Powers - Volume II. Leicester, UK: Harborough Publishing, 1942....

  • Hawker Horsley
    Hawker Horsley
    |-See also:-Bibliography:* Jarrett, Philip. "By Day and By Night: Hawker Horsley part 1". Aeroplane Monthly, Volume 21 No 10, Issue 246, October 1993. pp. 32–40....

  • Hawker Hotspur
    Hawker Hotspur
    |-See also:-Bibliography:* Brew, Alex. The Turret Fighters - Defiant and Roc. Ramsbury, Marlborough, Wiltshire, UK: Crowood Press, 2002. ISBN 1-86126-497-6....

  • Hawker Hurricane and Sea Hurricane
    Hawker Hurricane
    The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...


  • Hispano Aviación HA-1112
  • I.Ae. 30 Ñancú
    I.Ae. 30 Ñancú
    -See also:-References:NotesBibliography* Aero Fan n. 61 , April- June 1997.* aeroespacio.com, Buenos Aires: Aerospacio, 2002....

  • Miles M.20
    Miles M.20
    |-See also:-References:NotesBibliography* Amos, Peter and Don Lambert Brown. Miles Aircraft Since 1925, Volume 1. London: Putnam Aeronautical, 2000. ISBN 0-85177-787-0....

  • North American Mustang Mk X
  • Renard R.38
    Renard R-36
    The Renard R-36 was a Belgian all-metal fighter aircraft designed to replace the Fairey Firefly II within the Belgian Air Force. Designed to improve on the Renard Epervier, which was never adopted by the Belgian government, the prototype R-36 first flew on 5 November 1937...

  • Short Sturgeon
    Short Sturgeon
    The Short Sturgeon was a British aircraft originally designed in the Second World War as a high-performance torpedo bomber. With the end of the war in the Pacific it was no longer needed as such. Through shifting priorities postwar, the Sturgeon was redesigned first into a target tug and then later...

  • Supermarine Type 322
    Supermarine Type 322
    -See also:-Notes:The Albacore first flew on 12 December 1938.-References:*Andrews, C.F. and Morgan, E.B. Supermarine Aircraft since 1914. London: Putnam, 1987. ISBN 0 85177 800 3....

  • Supermarine Seafire
    Supermarine Seafire
    The Supermarine Seafire was a naval version of the Supermarine Spitfire specially adapted for operation from aircraft carriers. The name Seafire was arrived at by collapsing the longer name Sea Spitfire.-Origins of the Seafire:...

  • Supermarine Spitfire
    Supermarine Spitfire
    The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...

  • Tsunami Racer
    Tsunami Racer
    Tsunamiis an experimental American built aircraft. First flown August 17, 1986 by test pilot Steve Hinton, it was designed specifically to break the 3 km world speed record and to compete in Unlimited Air Racing. The aircraft was designed and built by Bruce Boland, Ray Poe and Pete Law...

  • Vickers F.7/41
    Vickers Type 432
    -Bibliography:* Buttler, Tony. Secret Projects: British Fighters and Bombers 1935 -1950 . Leicester, UK: Midland Publishing, 2004. ISBN 1-85780-179-2....

  • Vickers Wellington
    Vickers Wellington
    The Vickers Wellington was a British twin-engine, long range medium bomber designed in the mid-1930s at Brooklands in Weybridge, Surrey, by Vickers-Armstrongs' Chief Designer, R. K. Pierson. It was widely used as a night bomber in the early years of the Second World War, before being displaced as a...

  • Vickers Windsor
    Vickers Windsor
    |-See also:-References:NotesBibliography* Andrews, C.F. and E.B. Morgan. Vickers Aircraft since 1908. London: Putnam Aeronautical Books, 1988. ISBN 0-85177-815-1....

  • Westland Welkin
    Westland Welkin
    |-See also:-Bibliography:* Buttler, Tony. British Secret Projects: Fighters and Bombers 1935–1950. Hinckley, UK: Midland, 2004. ISBN 1-85780-179-2....



Postwar

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

, military transport aircraft
Military transport aircraft
Military transport aircraft are typically fixed and rotary wing cargo aircraft which are used to deliver troops, weapons and other military equipment by a variety of methods to any area of military operations around the surface of the planet, usually outside of the commercial flight routes in...

 such as the Avro York
Avro York
The Avro York was a British transport aircraft that was derived from the Second World War Lancaster heavy bomber, and used in both military and airliner roles between 1943 and 1964.-Design and development:...

, and the Canadair North Star
Canadair North Star
The Canadair North Star was a 1940s Canadian development of the Douglas C-54 / DC-4 aircraft. Instead of radial piston engines found on the Douglas design, Canadair employed Rolls-Royce Merlin engines in order to achieve a 35 mph faster cruising speed. The prototype flew on 15 July 1946 and...

 which performed in both roles. These engines were basically military specification with some minor changes to suit the different operating environment.

A Spanish-built version of the Messerschmitt Bf 109
Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...

 G-2, the 1954 Hispano Aviación HA-1112-M1L Buchon, was built in Hispano's
Hispano Aviacion
Hispano Aviación was a Spanish aircraft factory which began production in 1939, after a section of the Hispano-Suiza factory was isolated into a "Nationalist" area during the Spanish Civil War....

 factory in Seville
Seville
Seville is the artistic, historic, cultural, and financial capital of southern Spain. It is the capital of the autonomous community of Andalusia and of the province of Seville. It is situated on the plain of the River Guadalquivir, with an average elevation of above sea level...

 with the Rolls-Royce Merlin 500/45 engine of 1600 hp – 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.

The CASA 2.111
CASA 2.111
-See also:-References:NotesBibliography* Cruz, Gonzalo Avila. "Homegrown 'Pedros': Spanish-Built Heinkel He 111s: Part One-Jumo Variants". Air Enthusiast, No. 90, November/December 2000. Stamford, UK:Key Publishing, pp. 48–53. ISSN 0143-5450....

 was another Spanish-built version of a German aircraft, the Heinkel He 111
Heinkel He 111
The Heinkel He 111 was a German aircraft designed by Siegfried and Walter Günter in the early 1930s in violation of the Treaty of Versailles. Often described as a "Wolf in sheep's clothing", it masqueraded as a transport aircraft, but its purpose was to provide the Luftwaffe with a fast medium...

, that was adapted to use the Merlin after the supply of Junkers Jumo 211
Junkers Jumo 211
|-See also:-References:* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...

F-2 engines ran out at the end of the war. A similar situation existed with the Fiat G.59 when available stocks of the Italian licence-built version of the Daimler-Benz DB 605
Daimler-Benz DB 605
|-See also:-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7...

 engine ran short.

Alternative applications

A non-supercharged version of the Merlin using a larger proportion of steel and iron components was produced for use in tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

s. This engine, the Rolls-Royce Meteor
Rolls-Royce Meteor
The Rolls-Royce Meteor was a British tank engine of the Second World War.It was developed from the Rolls-Royce Merlin aero-engine by W. A. Robotham and his chassis design and development division at Belper, as they were not involved in aero-engine work...

, in turn led to the smaller Rolls-Royce Meteorite
Rolls-Royce Meteorite
The Rolls-Royce Meteorite, also known as the Rover Meteorite was a V8 petrol or diesel engine of capacity, and was derived from the Rolls-Royce Meteor. In essence it was two-thirds of a V12 Meteor, and it shared the Meteor's 60° vee angle...

.

In 1938, Rolls-Royce started work on modifying some Merlins which were later to be used in British MTBs
Motor Torpedo Boat
Motor Torpedo Boat was the name given to fast torpedo boats by the Royal Navy, and the Royal Canadian Navy.The capitalised term is generally used for the Royal Navy boats and abbreviated to "MTB"...

, MGBs
Motor Gun Boat
Motor Gun Boat was a Royal Navy term for a small military vessel of the Second World War. They were physically similar to the Motor Torpedo Boats but equipped with a mix of guns instead of torpedoes. Their small size and high speed made them difficult targets for E-boats or torpedo bombers, but...

, 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.

Experiments were carried out by the Irish Army
Irish Army
The Irish Army, officially named simply the Army is the main branch of the Defence Forces of Ireland. Approximately 8,500 men and women serve in the Irish Army, divided into three infantry Brigades...

 involving replacing the Bedford engine of a Churchill tank
Churchill tank
The Tank, Infantry, Mk IV was a heavy British infantry tank used in the Second World War, best known for its heavy armour, large longitudinal chassis with all-around tracks with multiple bogies, and its use as the basis of many specialist vehicles. It was one of the heaviest Allied tanks of the war...

 with a Rolls-Royce Merlin engine salvaged from an Irish Air Corps
Irish Air Corps
The Air Corps is the air component of the Defence Forces of Ireland providing support to the Army and Naval Service, together with non-military air services such as search and rescue and the Ministerial Air Transport Service...

 Seafire
Supermarine Seafire
The Supermarine Seafire was a naval version of the Supermarine Spitfire specially adapted for operation from aircraft carriers. The name Seafire was arrived at by collapsing the longer name Sea Spitfire.-Origins of the Seafire:...

 aircraft. The experiment was not a success, although the reasons are not recorded.

Survivors

One of the most successful of the World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 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
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 Battle of Britain Memorial Flight
Battle of Britain Memorial Flight
The Battle of Britain Memorial Flight is a Royal Air Force flight which provides an aerial display group comprising an Avro Lancaster, a Supermarine Spitfire and a Hawker Hurricane...

 is a notable current operator of the Merlin. In England the Shuttleworth Collection
Shuttleworth Collection
The Shuttleworth Collection is an aeronautical and automotive museum located at the Old Warden airfield in Bedfordshire, England. It is one of the most prestigious in the world due to the variety of old and well-preserved aircraft.- History :...

 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.

Engines on display


Many aerospace museums possess examples of the Merlin that are on public display:
  • Atlantic Canada Aviation Museum
    Atlantic Canada Aviation Museum
    The Atlantic Canada Aviation Museum is a Canadian aerospace museum located in the Halifax Regional Municipality in the province of Nova Scotia.It is the only museum devoted to preserving all aspects of Atlantic Canada's aviation heritage.-History:...

  • de Havilland Aircraft Heritage Centre
    De Havilland Aircraft Heritage Centre
    The de Havilland Aircraft Heritage Centre, formerly the Mosquito Aircraft Museum, is a volunteer-run aviation museum in London Colney, Hertfordshire, England...

  • Fantasy of Flight
    Fantasy of Flight
    Fantasy of Flight is an aviation-related attraction in Polk City, Florida, USA that takes visitors back to the pioneering days of early flight, World War I, World War II and beyond. The attraction opened in November of 1995, and houses the world's largest private aircraft collection on display...

  • Fleet Air Arm Museum
    Fleet Air Arm Museum
    The Fleet Air Arm Museum is located north of Yeovil, and south of Bristol. It has an extensive collection of military and civilian aircraft, as well as models of Royal Navy ships, especially aircraft carriers. Some of the museum has interactive displays...

  • Imperial War Museum Duxford
    Imperial War Museum Duxford
    Imperial War Museum Duxford is a branch of the Imperial War Museum near the village of Duxford in Cambridgeshire, England. Britain's largest aviation museum, Duxford houses the museum's large exhibits, including nearly 200 aircraft, military vehicles, artillery and minor naval vessels in seven...

  • Irish Air Corps Museum
  • Museum of Transport and Technology
    Museum of Transport and Technology
    The Museum of Transport and Technology is a museum located in Western Springs, Auckland, New Zealand. It is located close to the Western Springs Stadium, Auckland Zoo and the Western Springs Park. The museum has large collections of civilian and military aircraft and other land transport vehicles...

  • Museo Nacional de Aeronáutica de Argentina
    Museo Nacional de Aeronáutica de Argentina
    The Museo Nacional de Aeronáutica is a museum located in Morón, Buenos Aires, Argentina dedicated to the history of aviation, in particular the Argentine Air Force.-History:...

  • Polish Aviation Museum, Krakow (Cracow), Poland
    Polish Aviation Museum
    Polish Aviation Museum is a large museum of old 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 Austria-Hungary in 1912, is one of the oldest in the world...

  • Royal Air Force Museum Cosford
    Royal Air Force Museum Cosford
    The Royal Air Force Museum Cosford is a museum dedicated to the history of aviation, and the Royal Air Force in particular. The museum is a non-departmental public body sponsored by the Department for Culture, Media and Sport and a registered charity...

  • Royal Air Force Museum London
  • Science Museum (London)
    Science Museum (London)
    The Science Museum is one of the three major museums on Exhibition Road, South Kensington, London in the Royal Borough of Kensington and Chelsea. It is part of the National Museum of Science and Industry. The museum is a major London tourist attraction....

  • Shuttleworth Collection
    Shuttleworth Collection
    The Shuttleworth Collection is an aeronautical and automotive museum located at the Old Warden airfield in Bedfordshire, England. It is one of the most prestigious in the world due to the variety of old and well-preserved aircraft.- History :...


Specifications (Merlin 61)


See also

Further reading

  • Gunston, Bill. Development of Piston Aero Engines. Cambridge: Patrick Stephens, 2006. ISBN 0-7509-4478-1
  • Henshaw, Alex
    Alex Henshaw
    Alexander Adolphus Dumfries Henshaw MBE was a British air racer in the 1930s and a test pilot for Vickers Armstrong in the Second World War.-Early life:...

    . Sigh for a Merlin: Testing the Spitfire. London: Crecy, 1999 (2nd revised edition). ISBN 0-947554-83-1.
  • Jackson, Robert. The Encyclopedia of Military Aircraft Bath, UK: Parragon Books, 2006. ISBN 1-4054-2465-6.
  • Price, Alfred. Spitfire Mark I/II Aces 1939–41. London: Osprey Aerospace, 1996. ISBN 1-85532-627-2.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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