Rolls Royce Merlin Engine - The Most Unmistakeable Sound Of WW2The Rolls Royce Merlin is a liquid cooled 27 litre (1649 in3) 60° V12 piston aircraft engine which became famous in World War II. An English Icon , several versions of the Merlin were built by Rolls-Royce (in Derby, Crewe and Glasgow) by Ford of Britain (in Trafford Park, Manchester) and in the United States as the Packard V-1650. They are widely considered to be among the most successful aircraft engines produced during World War II.
The name 'Merlin' comes from a type of small falcon (Falco columbarius), in line with the convention Rolls-Royce used in naming its other piston aero-engines after birds of prey, and has no connection to King Arthur's legendary magician.
In the early 1930s, Rolls-Royce started planning for the future of its aero engine development programmes, and eventually settled on two basic designs. The 700 horsepower (500 kW) Rolls-Royce Peregrine was an updated, supercharged development of their existing V-12, 22 L Rolls-Royce Kestrel, which had been used with great success in a number of 1930s designs. Two Peregrines bolted together on a common crankshaft into an X-24 layout would create the 1,700 hp (1,300 kW) 44 L Rolls-Royce Vulture, for use in larger aircraft such as bombers. There was also the possibility that the famous 36 L 'R' engine (itself a development of the Rolls-Royce Buzzard, a scaled-up Kestrel) from the Supermarine racing planes could be developed into a 1,500 hp (1,100 kW) class engine of its own.
This left a large gap between 700 and 1,500 hp (500 and 1,100 kW), and to fill it work was started on a new 1,100 hp (820 kW) class design known as the PV-12 – PV for "private venture" as the company received no government money for work on the project. The PV-12 first flew in a Hawker Hart (serialled K3036) biplane on 21 February 1935, using the evaporative cooling system then in vogue, but this proved unreliable and so, when supplies of ethylene glycol from the US became available, the engine was changed to the conventional liquid cooling system. The Hart was subsequently delivered to Rolls-Royce and as a Merlin "Testbed" completed over 100 hour 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 310 mph (499 km/h). Fortunately, two designs had been developed; the Supermarine Spitfire and the Hawker Hurricane, the latter designed in response to another specification, F36/34. Both were designed around the PV-12 instead of the Kestrel, and were the only modern British fighters to have been so developed. Production contracts for both aircraft were placed in 1936. The PV-12 was given top priority and became the Rolls Royce Merlin.
Early Merlins were rather unreliable, but Rolls-Royce soon introduced a superb reliability-improvement programme. This consisted of taking random engines from the end of the assembly line and running them continuously at full power until they failed. They were then dismantled to find out which part had failed, and that part was redesigned to be stronger. After two years of this, the Rolls Royce Merlin had matured into one of the most reliable aero engines in the world, and could be run at full power for eight-hour bombing missions with no problems.
By the end of its production run, over 150,000 Merlin engines had been built. By mid 1943 the Merlin was supplemented in service by the larger Rolls-Royce Griffon which incorporated several design improvements.
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