Contents. Variant table Variant Take-off Power Combat Power Application Notes PV-12 740 hp (552 kW) at 12,000-foot (3,700 m) equivalent The initial design using an evaporative cooling system. Two built, passed Type Testing in July 1934. First flown 21 February 1935.

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Merlin B 950 hp (708 kW) at 11,000-foot (3,400 m) equivalent Two built, ethylene glycol liquid cooling system introduced. 'Ramp' ( were at a 45- angle to the cylinder). Passed Type Testing February 1935.

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Merlin C 950 hp (708 kW) at 11,000-foot (3,400 m) equivalent Development of Merlin B; and became three separate with bolt-on cylinder heads. First flight in 21 December 1935. Merlin E 955 hp (712 kW) constant output 1,045 hp (779 kW) maximum rating Similar 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 was the first production aircraft to be powered by the Merlin I and first flew on 10 March 1936. Merlin G 1,030 hp (768 kW) ( 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 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 I 890 hp (664 kW) at 2,850 rpm First production Merlin; 172 built. Merlin I through III used 100% coolant. Merlin II (RM 1S) 880 hp (656 kW) at 3,000 rpm 1,030 hp (768 kW) at 3,000 rpm at 5,500 ft (1,676 m) with + 6 psi (41 kPa) boost, Used 100% coolant. First production Merlin II delivered 10 August 1937. Merlin III (RM 1S) 880 hp (656 kW) at 3,000 rpm 1,310 hp (977 kW) at 3,000 rpm at 9,000 ft (2,743 m) with fuel and +12 psi (83 kPa) boost (5-minute limit)., Variant of Merlin II with universal propeller shaft, able to be fitted with or propellers. From late 1939, using fuel and + 12 psi (83 kPa) boost, the Merlin III developed 1,310 hp (977 kW) at 3,000 rpm at 9,000 ft (2,700 m). Later developing 1,440 hp (1,074 kW) at 3,000 rpm, +16 psi (110 kPa) boost at 5,500 ft (1,676 m) for the Sea Hurricane.

Using fuel the power ratings were the same as the Merlin II. First production Merlin III delivered 1 July 1938. Merlin VIII 1,080 hp (805 kW) at 3,000 rpm 1,275 hp (951 kW) at 3,000 rpm, +9 psi (62 kPa) boost, sea level with 100 octane Merlin X (RM 1SM) 1,280 hp (954 kW) at 3,000 rpm 1,280 hp (954 kW) at 3,000 rpm, +10 psi (69 kPa) boost, sea level, and 1,130 hp (843 kW) at 3,000 rpm at 5,250 ft (1,600 m) with maximum boost pressure +10 psi (69 kPa); this was the first production Merlin to use a two-speed supercharger; Used in, and bombers. First production Merlin X delivered 5 December 1938.

Merlin XII (RM 3S) 1,175 hp (876 kW) at 3,000 rpm 1,280 hp (954 kW) at 3,000 rpm, +12 psi (83 kPa) boost, 10,500 ft (3,200 m). 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 (83 kPa) using fuel. First production Merlin XII, 2 September 1939. Merlin XX (RM 3SM) 1,280 hp (954 kW) at 3,000 rpm 1,490 hp (1,111 kW) at 3,000 rpm, +16 psi (110 kPa) boost, with fuel at 12,500 ft (3,810 m)., and, First production version with two speed supercharger giving boost pressures of up to + 14 psi (97 kPa). First production Merlin XX, 4 July 1940.

^ Bridgeman 1998, pp. ^ Harvey-Bailey 1995, p. ^ Lumsden, Alec S. British piston aero-engines and their aircraft (1. In the UK ed.). Shrewsbury: Airlife Publ. Morgan and Shacklady 2000, p.

^ Lumsden 2003, p. ^ Morgan and Shacklady 2000, p. Lumsden 2003, p.204. ^ Bridgman 1998, p.

^ Robertson 1973, p.144. ^. ^ Jane's 100 Significant Aircraft, 1969. Price 1982, p.125.

Morgan and Shacklady 2000, p. Lumsden 2003, p.205.

Price 1982, pp.182,185. ^ Robertson 1973, p. ^ Price 1982, p. ^ Matusiak 2004, p. ^. Smith 1942, pp.

Smith 1942, p. ^ Air Ministry 1943, p.6. Air Ministry 1943, p. Lovesey 1946, p. Deutz 912 service manuals. Flight 1946, pp. Flight July 1946, p.

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. 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. External links Wikimedia Commons has media related to.