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List of Rolls-Royce Merlin variants

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List of Rolls-Royce Merlin variants

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Rolls-Royce Merlin 23

This is a list of Rolls-Royce Merlin variants. Engines of a similar power output were typically assigned different model numbers based on supercharger or propeller gear ratios, differences in cooling system or carburettors, engine block construction, starting system, or arrangement of engine controls. All Merlin engines except versions 131 and 135 were "right hand tractor", i.e. the propeller rotated clockwise viewed from behind.

Variant table

VariantTake-off powerCombat powerApplicationNotes
PV-12740 hp at 12000 ft equivalentThe initial design using an evaporative cooling system. Two built, passed bench Type Testing in July 1934. First flown 21 February 1935.
Merlin B950 hp at 11000 ft equivalentTwo built, ethylene glycol liquid cooling system introduced. "Ramp" cylinder heads (inlet valves were at a 45-degree angle to the cylinder). Passed Type Testing February 1935.
Merlin C950 hp at 11000 ft equivalentDevelopment of Merlin B; Crankcase and cylinder blocks became three separate castings with bolt-on cylinder heads. First flight in Hawker Horsley 21 December 1935.
Merlin E955 hp constant output1,045 hp maximum ratingSupermarine Spitfire prototypeSimilar to **C** with minor design changes. Passed 50-hour civil test in December 1935. Failed military 100-hour test in March 1936.
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 was the first production aircraft to be powered by the Merlin I and first flew on 10 March 1936.
Merlin G1,030 hp(**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 carried out at RAE 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 ramped up.
Merlin I890 hp at 2,850 rpmFairey Battle Mk.IFirst production Merlin; 172 built. Merlin I through III used 100% glycol coolant.
Merlin II *(RM 1S)*880 hp at 3,000 rpm1,030 hp at 3,000 rpm at 5,500 ft with + 6 psi boostSpitfire Mk.I, Defiant Mk.I, Hurricane Mk.I, Sea Hurricane Mk.I, Battle Mk.IUsed 100% glycol coolant. First production Merlin II delivered 10 August 1937.
Merlin III *(RM 1S)*880 hp at 3,000 rpm1,310 hp at 3,000 rpm at 9,000 ft with [100 octane](100-octane) fuel and +12 psi boost (5-minute limit).Spitfire Mk.I, Defiant Mk.I, Hurricane Mk.I, Sea Hurricane Mk.I, Battle Mk.I12psikPaabbr=on0}} boost, the Merlin III developed 1,310 hp at 3,000 rpm at 9000 ft. Later developing 1,440 hp at 3,000 rpm, +16 psi boost at 5,500 ft for the Sea Hurricane. Using [87 Octane](87-octane) fuel the power ratings were the same as the Merlin II. First production Merlin III delivered 1 July 1938.
Merlin VIII *(RM 3M)*1,080 hp at 3,000 rpm1,275 hp at 3,000 rpm, +9 psi boost, sea level with 100 octaneFulmar Mk.ILower gearing on supercharger to give improved performance at low altitudes
Merlin X *(RM 1SM)*1,280 hp at 3,000 rpm1,280 hp at 3,000 rpm, +10 psi boost, sea levelHalifax Mk.I, Wellington Mk.II, Whitley Mk.V and Whitley Mk.VII1,130 hp at 3,000 rpm at 5,250 ft with 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 delivered 5 December 1938.
Merlin XII *(RM 3S)*1,175 hp at 3,000 rpm1,280 hp at 3,000 rpm, +12 psi boost, 10,500 ftSpitfire Mk.IICoffman cartridge starter. First version of Merlin to use 30/70% glycol/water coolant with reinforced construction, able to use constant boost pressure of up to +12 psi using [100 octane](100-octane) fuel.
Merlin XX *(RM 3SM)*1,280 hp at 3,000 rpm1,490 hp at 3,000 rpm, +16 psi boost, with [100 Octane](100-octane) fuel at 12,500 ft.Beaufighter Mk.II, Defiant Mk.II, Halifax Mk.II, Halifax Mk.V, Hurricane Mk.II and Hurricane Mk.IV, Lancaster Mk.I, Lancaster Mk.III, Spitfire Mk.IIIHad a two speed supercharger giving boost pressures of up to + 14 psi. First production Merlin XX, 4 July 1940.
Merlin 21 *(RM 3SM)*1,280 hp at 3,000 rpm1,490 hp at 3,000 rpm, +16 psi boost, 12,500 ftde Havilland Mosquito Mk.I, Mk.II, Mk.III, Mk.IV and Mk.VIMerlin XX with direction of coolant flow reversed for Mosquito wing radiator installation
Merlin 22 *(RM 3SM)*1,390 hp at 3,000 rpm1,435 hp at 3,000 rpm, +16 psi boost, 11,000 ftLancaster Mk.I, York Mk.ISimilar to Merlin XX with two-piece cylinder block designed by Rolls-Royce
Merlin 23 *(RM 3SM)*1,390 hp at 3,000 rpm1,435 hp at 3,000 rpm, +16 psi boost, 11,000 ftde Havilland Mosquito Mk.I, Mk.II, Mk.IV, Mk.VI, Mk.XII and Mk.XIIIMerlin 22 with direction of coolant flow reversed for Mosquito wing radiator installation
Merlin 24 *(RM 3SM)*1,610 hp at 3,000 rpm1,510 hp at 3,000 rpm, +18 psi boost, 9,250 ftLancaster Mk.I, Lancaster Mk.VII, York Mk.I and Halifax Mk.IISimilar to Merlin 22 but with improved boost control to permit increased ratings
Merlin 25 *(RM 3SM)*1,610 hp at 3,000 rpm1,510 hp at 3,000 rpm, +18 psi boost, 9,250 ftde Havilland Mosquito Mk.VI and Mk.XIXMerlin 24 with direction of coolant flow reversed for Mosquito wing radiator installation
Merlin 27 *(RM 3SM)*1,610 hp at 3,000 rpm1,510 hp at 3,000 rpm, +18 psi boost, 9,250 ftHurricane Mk.IVAs Merlin 22 with different gar reduction ratio
Merlin 28 *(RM 3SM)*1,300 hp at 3,000 rpm1,240 hp at 3,000 rpm, +9 psi boost, 11,500 ftLancaster Mk.III, Kittyhawk II (Curtiss P-40F)Built by Packard, similar to Merlin XX with two-piece cylinder block designed by Packard. Known as the V-1650-1 when supplied to USAAF
Merlin 29 *(RM 3SM)*1,300 hp at 3,000 rpm1,240 hp at 3,000 rpm, +9 psi boost, 11,500 ftHurricane Mk.XII (Canadian-built), Kittyhawk II (Curtiss P-40F)Similar to Merlin 28 with different reduction gear ratio and propeller shaft splined to suit American propellers
Merlin 30 *(RM 2M)*1,300 hp at 3,000 rpm1,360 hp at 3,000 rpm, +12 psi boost, 6,000 ftBarracuda Mk.I and Fulmar Mk.IISimilar to Merlin VIII but different supercharger (smaller diameter impeller with higher gearing)
Merlin 31 *(RM 3SM)*1,300 hp at 3,000 rpm1,240 hp at 3,000 rpm, +9 psi boost, 11,500 ftMosquito Mk.XX (Canadian), Mosquito Mk.40 (Australia)Packard-built version of Merlin 21
Merlin 32 *(RM 5M)*1,620 hp at 3,000 rpm1,640 hp at 3,000 rpm, +18 psi boost, 2,000 ftBarracuda Mk.II, Seafire Mk.II, Hurricane Mk.V, Spitfire PR Mk. XIIIA "low altitude" version of Merlin with cropped supercharger impellers for increased power at lower altitudes, as per the Merlin XXX; fitted with a Coffman engine starter; used mainly in Fleet Air Arm aircraft. First production Merlin 32 delivered 17 June 1942.
Merlin 33 *(RM 3SM)*1,400 hp at 3,000 rpm1,400 hp at 3,000 rpm, +9 psi boost, 11,500 ftMosquito XX (Canadian), Mosquito 40 (Australia)Packard-built Merlin 23
Merlin 351,280 hp at 3,000 rpm, 54.3 inHg +12 psi boost1,245 hp at 3,000 rpm at 11500 ftBoulton Paul Balliol, Avro AthenaMerlin T24-2 with single-speed, single-stage supercharger
Merlin 38 *(RM 3SM)*1,400 hp at 3,000 rpm1,400 hp at 3,000 rpm, +9 psi boost, 11,500 ftLancaster I and IIIPackard-built Merlin 22
Merlin 45 *(RM 5S)*1,185 hp at 3,000 rpm1,515 hp at 3,000 rpm, +16 psi boost, 11,500 ftSpitfire Mk.V, Spitfire PR Mk.IG (later redesignated Spitfire PR.VII), Spitfire PR Mk.IV, Seafire Mk.IB, Seafire Mk.IICA variant of the Merlin XX fitted with single-stage, single-speed supercharger for Spitfire use. First production Merlin 45 delivered 13 January 1941. First of specialised engines for Spitfire Mk V variants and early Seafires.
Merlin 45M1,230 hp at 3,000 rpm1,585 hp at 3,000 rpm, +18 psi boost, 2,750 ftSpitfire LF Mk.VVersion of Merlin 45 with "cropped" (smaller diameter) supercharger impeller allowing greater boost at low altitudes.
Merlin 46 *(RM 6S)*1,100 hp at 3,000 rpm1,415 hp at 3,000 rpm, +16 psi boost, 14,000 ftSpitfire Mk.V, Spitfire PR Mk.IV, Spitfire Mk.VII, Seafire Mk.IB and Seafire Mk.IICSimilar to Merlin 45 with larger supercharger impeller diameter
Merlin 47 *(RM 6S)*1,100 hp at 3,000 rpm1,415 hp at 3,000 rpm, +16 psi boost, 14,00 ftSpitfire HF Mk.VI high-altitude intercepterSimilar to Merlin 46 with a Marshall compressor (often called a "blower") to pressurise the cockpit. First production Merlin 47 delivered 2 December 1941.
Merlin 50 *(RM 5S)*1,185 hp at 3,000 rpm1,470 hp at 3,000 rpm, +16 psi boost, 9,250 ftSpitfire Mk.VLow-altitude version with supercharger impeller "cropped" to 9.5 in in diameter. **Merlin 50** series was first to use the Bendix Stromberg "negative-g" carburettor.
Merlin 50M *(RM 5S)*1,230 hp at 3,000 rpm1,585 hp at 3,000 rpm, +18 psi boost, 2,750 ftSpitfire LF Mk.VSimilar to Merlin 50 with smaller diameter supercharger impeller
Merlin 55 *(RM 5S)*1,185 hp at 3,000 rpm1,470 hp at 3,000 rpm, +16 psi, 9,250 ftSpitfire Mk.V and Seafire Mk.IIISimilar to Merlin 45 but with two-piece cylinder blocks
Merlin 55M *(RM 5S)*1,230 hp at 3,000 rpm1,585 hp at 3,000 rpm, +18 psi boost, 2,750 ftSpitfire LF Mk.V, Seafire Mk.IIIVariant with "cropped" supercharger impellor
Merlin 60 *(RM 6SM)*1,390 hp at 3,000 rpm1,110 hp at 2,850 rpm, +9 psi boost, 29,000 ftWellington Mk.VIFirst variant fitted with two-stage, two-speed supercharger; rated for high altitude.
Merlin 61 *(RM 8SM)*1,280 hp at 3,000 rpm1,565 hp at 3,000 rpm, +15 psi boost, 11,250 ftSpitfire Mk.IX and Spitfire PR Mk.XIProduction variant of Merlin 60 fitted with a new two-speed two-stage supercharger providing increased power at medium to high altitudes. First British production variant to incorporate two-piece cylinder blocks designed by Rolls-Royce for the Packard Merlin. First production Merlin 61 delivered 2 March 1942.
Merlin 62 *(RM 6SM)*1,390 hp at 3,000 rpm1,110 hp at 2,850 rpm, +9 psi boost, 29,000 ftWellington Mk.VISimilar to Merlin 60 but with two-piece cylinder blocks
Merlin 63 *(RM 8SM)*1,280 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi boost, 8,500 ftSpitfire Mk.VIII, IX, PR.XIReplaced Merlin 61
Merlin 63A *(RM 8SM)*1,280 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi boost, 8,500 ftSpitfire PR Mk.XIMerlin 63 with crankcase from Merlin 64, but no blower and blanking covers fitted
Merlin 64 *(RM 8SM)*1,280 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi boost, 8,500 ftSpitfire Mk.VIICabin pressure blower
Merlin 66 *(RM 10SM)*1,315 hp at 3,000 rpm1,705 hp at 3,000 rpm, +18 psi boost, 5,750 ftSpitfire LF Mk.VIII LF Mk.IXFitted with supercharger rated for low altitude; Bendix-Stromberg anti-g carburettor
Merlin 67 *(RM 10SM)*1,315 hp at 3,000 rpm1,705 hp at 3,000 rpm, +18 psi boost, 5,750 ftSimilar to Merlin 66 but with reversed coolant flow and 0.42 reduction gear. No production.
Merlin 681,670 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi boost, 6,400 ftAvro Lincoln, Mustang III (North American P-51B and C)Packard-built version of Merlin 85. Produced for USAAF as Packard V-1650-7
Merlin 691,315 hp at 3,000 rpm1,705 hp at 3,000 rpm, +18 psi boost, 5,750 ftde Havilland MosquitoPackard version of Merlin 67 - similar to Merlin 66 but with reversed coolant flow and 0.42 reduction gear
Merlin 70 *(RM 11SM)*1,250 hp at 3,000 rpm1,655 hp at 3,000 rpm, +18 psi boost, 10,000 ftSpitfire HF Mk.VIII HF.IX, PR.XIBendix Stromberg anti-g carburettor
Merlin 71 *(RM 11SM)*1,250 hp at 3,000 rpm1,655 hp at 3,000 rpm, +18 psi, 10,000 ftSpitfire HF Mk.VIIBendix Stromberg]] anti-g carburettor
Merlin 72 *(RM 8SM)*1,280 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi, 8,500 ftde Havilland Mosquito PR Mk.IX, B Mk.IX, Mk.XVI and Mk.30. Welkin Mk.ISimilar to Merlin 63 but with reversed coolant flow
Merlin 73 *(RM 8SM)*1,280 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi, 8,500 ftde Havilland Mosquito Mk.XVI, Welkin Mk.ISame as Merlin 72 with a cabin pressure blower
Merlin 76 *(RM 11SM)*1,250 hp at 3,000 rpm1,655 hp at 3,000 rpm, +18 psi, 10,000 ftde Havilland Mosquito PR Mk.XVI, Mk.30, Welkin Mk.I1,233 hp at 35,000 ft; Fitted with a two-speed, two-stage supercharger and a Bendix Stromberg anti-g carburettor. Dedicated "high altitude" version used in the Westland Welkin high-altitude fighter, and some later Spitfire and de Havilland Mosquito variants.
Merlin 77 *(RM 11SM)*1,250 hp at 3,000 rpm1,655 hp at 3,000 rpm, +18 psi, 10,000 ftde Havilland Mosquito Mk.XVI, Welkin Mk.I, Spitfire PR Mk.XSame as Merlin 76 with a pressurising blower
Merlin 85 *(RM 10SM)*1,635 hp at 3,000 rpm1,705 hp at 3,000 rpm, +18 psi, 5,750 ftLancaster Mk.VI and Lincoln Mk.IGenerally similar to Merlin 66 but with 0.42 reduction gear ratio and intercooler header tank integral with intercooler
Merlin 130/131 *(RM 14SM)*2,070 hp at 3,000 rpmde Havilland Hornet F Mk.1, PR Mk.2, F Mk.3, FR Mk.4.Redesigned "slimline" versions for the de Havilland Hornet. Engine modified to decrease frontal area to a minimum and was the first Merlin series to use down-draught induction systems. Coolant pump moved from the bottom of the engine to the starboard side. Two-speed, two-stage supercharger and S.U. injection carburettor giving a maximum boost of +25 psi. On the Hornet the Merlin 130 was fitted in the starboard nacelle: 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.
Merlin 134/135 *(RM 14SM)*2,030 hp at 3,000 rpmde Havilland Sea Hornet F Mk.20, NF Mk.21 and PR Mk.22Derated 130/131 with maximum boost lowered to +18 psi. With Corliss throttle.
Merlin 224 *(RM 3SM)*1,635 hp at 3,000 rpm1,680 hp at 3,000 rpm, +18 psi, 2,750 ftAvro Lancaster Mk.I, Mk.III and Mk.XPackard-built Merlin 24
Merlin 225 *(RM 3SM)*1,635 hp at 3,000 rpm1,680 hp at 3,000 rpm, +18 psi, 2,500 ftde Havilland Mosquito Mk.25 and Mk.26Packard-built Merlin 25
Merlin 266 *(RM 10SM)*1,670 hp at 3,000 rpm1,710 hp at 3,000 rpm, +18 psi, 6,400 fttSpitfire LF Mk.XVIThe prefix "2" indicates engines built by Packard, otherwise as Merlin 66, optimised for low-altitude operation.
Merlin 6201,175 hp continuous cruising using 2,650 rpm at + 9 psiAvro Tudor, Avro York, and Canadair North StarCapable of emergency rating of 1,795 hp at 3,000 rpm using +20 psi ; civilian engine developed from Merlin 102; two-stage supercharger optimised for medium altitudes, and used an S.U. injection carburettor. Universal Power Plant (UPP) installation similar to that used on Avro Lincoln. The Merlin 620-621 series was designed to operate in the severe climatic conditions encountered on Canadian and long-range North Atlantic air routes.
A left side view of a gloss grey -painted aircraft piston engine on static display
Preserved Merlin XX at the [[Royal Air Force Museum London
Audio of RR Merlin 66/266 starting.
A sectioned, parallel valve, aircraft engine cylinder head is shown with colour-coded internal details. Coolant passageways are painted green; the valves, valve springs, camshaft and rocker arms are also shown.
Parallel valve Merlin cylinder head

References

Notes

Bibliography

  • Air Ministry. Pilot's Notes for Spitfire Mark F.VII - Merlin 64 or 71 engine; Mark F.VIII-Merlin 63,66 or 70 engine. Air Publication 1565G & H -P.N. London, UK: Air Ministry, December 1943.
  • Bridgman, L. Jane's fighting aircraft of World War II. London: Crescent, 1998.
  • Harvey-Bailey, A. The Merlin in Perspective - the combat years Derby, England: Rolls-Royce Heritage Trust, 1983.
  • Harvey-Bailey, A. The Merlin in Perspective - the combat years Derby, England: Rolls-Royce Heritage Trust, 4th edition 1995.
  • Harvey-Bailey, Alec and Piggott, Dave The Merlin 100 Series – The Ultimate Military Development Derby, England: Rolls-Royce Heritage Trust, 1993.
  • Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. .
  • Price, Alfred. The Spitfire Story. London: Jane's Publishing Company Ltd., 1982. .
  • Robertson, Bruce. Spitfire: The Story of a Famous Fighter. Hemel Hempstead, Hertfordshire, UK: Model & Allied Publications Ltd., 1960. Third revised edition 1973. .

References

  1. Bridgeman 1998, pp. 281–283.
  2. Lumsden 2003, p. 203.
  3. Morgan and Shacklady 2000, p. 607.
  4. Lumsden 2003, p. 204.
  5. Morgan and Shacklady 2000, p. 610.
  6. Bridgman 1998, p. 281.
  7. Robertson 1973, p.144.
  8. Harvey-Bailey 1995, p. 155.
  9. First production Merlin XII, 2 September 1939.Jane's 100 Significant Aircraft, 1969.
  10. Price 1982, p.125.
  11. Morgan and Shacklady 2000, p. 129.
  12. Lumsden 2003, p.205.
  13. Harvey-Bailey 1995, Appendix VII
  14. Harvey-Bailey 1995, Appendix VII
  15. Price 1982, pp.182,185.
  16. Robertson 1973, p. 145.
  17. Price 1982, p. 145.
  18. Matusiak 2004, p. 10.
  19. [http://www.spitfireperformance.com/w3228.html Spitfire V performance]
  20. Harvey-Bailey and Piggott 1993, p. 172.
  21. Smith 1942, pp. 655–659.
  22. Smith 1942, p. 656.
  23. Air Ministry 1943, p.6.
  24. Harvey-Bailey and Piggott 1993, p. 173
  25. Air Ministry 1943, p. 6.
  26. Harvey-Bailey and Piggott 1993, p. 174
  27. Lovesey 1946, p. 219.
  28. Flight 1946, pp. 92–94.
  29. Harvey-Bailey and Piggott, 1993, p. 177
  30. Harvey-Bailey and Piggott, 1993, p. 178
  31. Flight July 1946, p. 99.
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