Hawker Aircraft Since 1920 (3rd revised edition).
Irish Army Vehicles, Transport and Armour since 1922.
Merlin engines remain in Royal Air Force service today with the Battle of Britain Memorial Flight, and power many restored aircraft in private ownership worldwide. ==Design and development== ===Origin=== In the early 1930s, Rolls-Royce started planning its future aero-engine development programme and realised there was a need for an engine larger than their 21-litre (1,296 cu in) Kestrel which was being used with great success in a number of 1930s aircraft.
Rolls-Royce designed the engine and first ran it in 1933 as a private venture.
The PV-12 was first run on 15 October 1933 and first flew in a Hawker Hart biplane (serial number K3036) on 21 February 1935.
Two built, passed bench type testing in July 1934, generating 740 horsepower (552 kW) at equivalent.
The PV-12 was first run on 15 October 1933 and first flew in a Hawker Hart biplane (serial number K3036) on 21 February 1935.
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 issued a specification, F10/35, for new fighter aircraft with a minimum airspeed of .
First flown 21 February 1935. Merlin B Two built, ethylene glycol liquid cooling system introduced.
Passed Type Testing February 1935, generating 950 horsepower (708 kW) at equivalent. Merlin C Development of Merlin B; crankcase and cylinder blocks became three separate castings with bolt-on cylinder heads.
First flight in Hawker Horsley 21 December 1935, 950 horsepower (708 kW) at . 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).
By the end of its production run in 1950, 168,176 Merlin engines had been built; over 112,000 in Britain and more than 55,000 under licence in the U.S. ===Derby=== The existing Rolls-Royce facilities at Osmaston, Derby were not suitable for mass engine production although the floor space had been increased by some 25% between 1935 and 1939; Hives planned to build the first two- or three hundred engines there until engineering teething troubles had been resolved.
Initially known as the PV-12, it was later called Merlin following the company convention of naming its piston aero engines after birds of prey. After several modifications, the first production variants of the PV-12 were completed in 1936.
Production contracts for both aircraft were placed in 1936, and development of the PV-12 was given top priority as well as government funding.
Failed military 100-hour test in March 1936.
First flight in Horsley 16 July 1936.
The Fairey Battle I 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 (valve stems parallel to the cylinder bore axis) scaled up from the Kestrel engine.
400-hour flight endurance tests carried out at RAE July 1937; acceptance test 22 September 1937.
Formed basis for the Rolls-Royce/Rover Meteor tank engine "Racing" Merlin Racing engine for 1937/38 "Speed Spitfire" world speed record attempt.
First of Rolls-Royce unitised "Power Plant" installation designs for this engine in 1937 and used in Handley Page Halifax I, Vickers Wellington II, and Armstrong Whitworth Whitley V and VII. Merlin XII Merlin fitted with 0.477:1 reduction gear installed in some Spitfire II's with three-bladed Rotol constant-speed propeller.
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.
First production Merlin II delivered 10 August 1937.
It was first widely delivered as the 1,030-horsepower (770 kW) Merlin II in 1938, and production was quickly stepped up for Fairey Battle II. Merlin III Merlin II with standardised de Havilland/Rotol SBAC propeller shaft, and dual accessory-drive.
In 1938 Stanley Hooker, an Oxford graduate in applied mathematics, explained "... I soon became very familiar with the construction of the Merlin supercharger and carburettor ...
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.
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 original factory closed in March 2008, but the company maintains a presence in Derby. ===Crewe=== To meet the increasing demand for Merlin engines, Rolls-Royce started building work on a new factory at Crewe in May 1938, with engines leaving the factory in 1939.
First production Merlin III delivered 1 July 1938. Merlin X (RM 1SM) 1,130 hp (840 kW) at 3,000 rpm at ; 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, 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; first version to use 70/30% water/glycol coolant rather than 100% glycol.
In 1943, further Meteor development was handed over to Rover, in exchange for Rover's gas turbine interests. In 1938, Rolls-Royce started work on modifying some Merlins which were later to be used in British MTBs, MGBs, and RAF Air-Sea Rescue Launches.
1563, Volume XXXIV, 8 December 1938. "Rolls-Royce Merlin 130 Series (article and images)." Flight No.
By the end of its production run in 1950, 168,176 Merlin engines had been built; over 112,000 in Britain and more than 55,000 under licence in the U.S. ===Derby=== The existing Rolls-Royce facilities at Osmaston, Derby were not suitable for mass engine production although the floor space had been increased by some 25% between 1935 and 1939; Hives planned to build the first two- or three hundred engines there until engineering teething troubles had been resolved.
To fund this expansion, the Air Ministry had provided a total of £1,927,000 by December 1939.
The original factory closed in March 2008, but the company maintains a presence in Derby. ===Crewe=== To meet the increasing demand for Merlin engines, Rolls-Royce started building work on a new factory at Crewe in May 1938, with engines leaving the factory in 1939.
In September 1939, the Air Ministry allocated £4,500,000 for a new Shadow factory.
This government-funded and -operated factory was built at Hillington starting in June 1939 with workers moving into the premises in October, one month after the outbreak of war.
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 ; using 87-octane fuel the power ratings were the same as the Merlin II.
First production Merlin XII, 2 September 1939. Merlin XX (RM 3SM) 1,480 hp (1,105 kW) at 3,000 rpm at ; two-speed supercharger; boost pressure of up to +14 psi; Used in Hurricane Mk.II, Beaufighter Mk.II, Halifax Mk.II and Lancaster Mk.I bombers, and in the Spitfire Mk.III prototypes (N3297 & W3237).
"Development of the Rolls-Royce Merlin from 1939 to 1945." Aircraft Engineering and Aerospace Technology, Volume 18, Issue 7.
Spitfire Mark I/II Aces 1939–41.
In 1940 a strike took place when women replaced men on capstan lathes, the workers' union insisting this was a skilled labour job; however, the men returned to work after 10 days. Total Merlin production at Crewe was 26,065. The factory was used postwar for the production of Rolls-Royce and Bentley motor cars and military fighting vehicle power plants.
The factory was fully occupied by September 1940.
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.
Finally, following the production of the Rolls-Royce Avon turbojet and others, the factory was closed in 2005. ===Manchester=== The Ford Motor Company was asked to produce Merlins at Trafford Park, Stretford, near Manchester, and building work on a new factory was started in May 1940 on a site.
in July 1940, and the Packard Motor Car Company was subsequently selected to take on the $130,000,000 Merlin order (equivalent to $ in dollars).
Agreement was reached in September 1940, and the first Packard-built engine, a Merlin XX designated the V-1650-1, ran in August 1941. Total Merlin production by Packard was 55,523. Six development engines were also made by Continental Motors, Inc. ==Variants== This is a list of representative Merlin variants, describing some of the mechanical changes made during development of the Merlin.
First production Merlin XX, 4 July 1940. Merlin 32 (RM 5M) 1,645 hp (1,230 kW) at 3,000 rpm at ; a "low altitude" version of Merlin with cropped supercharger impellers for increased power at lower altitudes and a maximum boost pressure of +18 psi; fitted with Coffman engine starter; used mainly in Fleet Air Arm aircraft, mainly the Fairey Barracuda Mk.II torpedo bomber and Supermarine Seafire F.
A.P 1509B/J.2-W Merlin II and III Aero Engines (June 1940).
London: Air Ministry, 1940. Air Ministry.
A.P 1565B Spitfire IIA and IIB Aeroplanes: Merlin XII Engine, Pilot's Notes (July 1940).
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.
Built with two distinct sections to minimise potential bomb damage, it was completed in May 1941 and bombed in the same month.
Agreement was reached in September 1940, and the first Packard-built engine, a Merlin XX designated the V-1650-1, ran in August 1941. Total Merlin production by Packard was 55,523. Six development engines were also made by Continental Motors, Inc. ==Variants== This is a list of representative Merlin variants, describing some of the mechanical changes made during development of the Merlin.
First production Merlin 45, 13 January 1941. Merlin 47 (RM 6S) 1,415 hp (1,055 kW) at 3,000 rpm at ; high-altitude version used in Spitfire H.F.Mk.VI.
First production Merlin 47, 2 December 1941. Merlin 50.M (RM 5S) 1,585 hp (1,182 kW) at 3,000 rpm at ; low-altitude version with supercharger impeller "cropped" to in diameter.
London: Collins Clear-Type Press, 1941. Berger, Monty and Street, Brian Jeffrey.
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.
First production Merlin 32, 17 June 1942. Merlin 45 (RM 5S) 1,515 hp (1,130 kW) at 3,000 rpm at ; used in Spitfire Mk.V, PR.Mk.IV and PR.Mk.VII, Seafire Ib and IIc.
First production Merlin 61, 2 March 1942. Merlin 63 & 63A 1,710 hp (1,275 kW) at 3,000 rpm at , 1,505 hp (1,122 kW) at 3,000 rpm at ; strengthened two-speed two-stage development of Merlin 61; +18 psi boost; Reduction gear ratio .477:1; Merlin 63A did not have extra gears for pressurisation and incorporated a strengthened supercharger drive quill shaft.
1731, Volume XLI, 26 February 1942. Smith, G.
1773, Volume XLII, 17 December 1942. Tanner, John.
With the Merlin itself soon pushing into the range, the Peregrine and Vulture were both cancelled in 1943, and by mid-1943 the Merlin was supplemented in service by the larger Griffon.
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 pressure carburettor that injected fuel at 5 pounds per square inch (34 kPa; 0.34 bar) through a nozzle directly into the supercharger, and was fitted to Merlin 66, 70, 76, 77 and 85 variants.
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".
Despite this, the first Merlin engine came off the production line one month later and it was building the engine at a rate of 200 per week by 1943, at which point the joint factories were producing 18,000 Merlins per year.
In 1943, further Meteor development was handed over to Rover, in exchange for Rover's gas turbine interests. In 1938, Rolls-Royce started work on modifying some Merlins which were later to be used in British MTBs, MGBs, and RAF Air-Sea Rescue Launches.
London, UK: Air Ministry, December 1943. Beckles, Gordon.
With this boost rating the Merlin 66 generated 2,000 hp (1,491 kW) at sea level and 1,860 hp (1,387 kW) at . Starting in March 1944, the Merlin 66-powered Spitfire IXs of two Air Defence of Great Britain (ADGB) squadrons were cleared to use the new fuel for operational trials, and it was put to good use in the summer of 1944 when it enabled Spitfire L.F.
In early February 1945, Spitfires of the Second Tactical Air Force (2TAF) also began using 100/150 grade fuel.
Merlin production started to run down in August 1945, and finally ceased on 23 March 1946. Total Merlin production at Trafford Park was 30,428. ===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.
"Development of the Rolls-Royce Merlin from 1939 to 1945." Aircraft Engineering and Aerospace Technology, Volume 18, Issue 7.
Civil Merlin engines in airline service flew 7,818,000 air miles in 1946, 17,455,000 in 1947, and 24,850,000 miles in 1948. ====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" aluminium alloy having separate heads and skirts.
Merlin production started to run down in August 1945, and finally ceased on 23 March 1946. Total Merlin production at Trafford Park was 30,428. ===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.
London, MCB UP Ltd., July 1946.
Aircraft Engines of the World 1946 (3rd ed.).
London: Sir Isaac Pitman and Sons, 1946. "Some Trends in engine design (article and images)." Flight No.
1935, Volume XLIX, 24 January 1946. "Two New Power Units (article and images)." Flight and The Aircraft Engineer No.
1961, Volume L, 25 July 1946. ==Further reading== Gunston, Bill.
Civil Merlin engines in airline service flew 7,818,000 air miles in 1946, 17,455,000 in 1947, and 24,850,000 miles in 1948. ====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" aluminium alloy having separate heads and skirts.
Civil Merlin engines in airline service flew 7,818,000 air miles in 1946, 17,455,000 in 1947, and 24,850,000 miles in 1948. ====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" aluminium alloy having separate heads and skirts.
Production ceased in 1950 after a total of almost 150,000 engines had been delivered.
By the end of its production run in 1950, 168,176 Merlin engines had been built; over 112,000 in Britain and more than 55,000 under licence in the U.S. ===Derby=== The existing Rolls-Royce facilities at Osmaston, Derby were not suitable for mass engine production although the floor space had been increased by some 25% between 1935 and 1939; Hives planned to build the first two- or three hundred engines there until engineering teething troubles had been resolved.
By 1951 the time between overhauls (TBO) was typically 650–800 hours depending on use.
2363, Volume 65, 7 May 1954. Lloyd, Ian and Pugh, Peter.
Hemel Hempstead, Hertfordshire, UK: Model & Allied Publications, 1960.
London: Constable, 1970.
London: Her Majesty's Stationery Office, 1971. Price, Alfred.
London: Air Data Publications, 1972 (reprint).
Third revised edition 1973.
London: Arms and Armour Press, 1981.
London: Jane's Publishing Company, 1982.
Hooker, Stanley Not Much of an Engineer London: Airlife, 1984.
Derby, England: Rolls-Royce Heritage Trust, 1990.
Shrewsbury, UK: Airlife, 1991.
London: Putnam, 1991.
Toronto, Canada: Random House, 1994.
New York: Smithmark Publishers, 1994.
The Merlin in Perspective – The Combat Years (4th edition) Derby, England: Rolls-Royce Heritage Trust, 1995.
Warrendale, Pennsylvania: SAE International, 1995.
London: Osprey Aerospace, 1996.
In 1998 Volkswagen AG bought the Bentley marque and the factory.
London: Crescent, 1998.
London: Crecy, 1999 (2nd revised edition).
London: Key Publishing, 2000.
Marlborough, Wiltshire: Airlife Publishing, 2003.
Cambridge, England: Icon Books, 2004.
Redbourn, UK: Mushroom Model Publications, 2004.
Finally, following the production of the Rolls-Royce Avon turbojet and others, the factory was closed in 2005. ===Manchester=== The Ford Motor Company was asked to produce Merlins at Trafford Park, Stretford, near Manchester, and building work on a new factory was started in May 1940 on a site.
Stroud, UK: Sutton Publishing, 2006.
Cambridge: Patrick Stephens, 2006.
The Encyclopedia of Military Aircraft Bath, UK: Parragon Books, 2006.
London: John Murray, 2007.
The original factory closed in March 2008, but the company maintains a presence in Derby. ===Crewe=== To meet the increasing demand for Merlin engines, Rolls-Royce started building work on a new factory at Crewe in May 1938, with engines leaving the factory in 1939.
Botley, UK: Osprey Publishing Limited, 2010.
Barnsley, Yorkshire UK: Pen & Sword Books, 2011.
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