Rolls-Royce Merlin

The Rolls-Royce Merlin is a British liquid-cooled, V-12, piston aero engine, of 27-litre (1,650cu in) capacity. Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin following the company convention of naming its piston aero engines after birds of prey. 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, Hawker Hurricane and Supermarine Spitfire. More Merlins were made for the four-engined Avro Lancaster 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, Crewe and Glasgow, as well as by Ford of Britain at their Trafford Park factory, near Manchester. The Packard V-1650 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 airliners and military transport aircraft.


In military use the Merlin was superseded by its larger capacity stablemate, the Rolls-Royce Griffon. 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.


General characteristics

  • Type: 12-cylinder, supercharged, liquid-cooled, 60 "Vee", piston aircraft engine.
  • Bore: 5.4in (137mm)
  • Stroke: 6.0in (152mm)
  • Displacement: 1,647cuin (27L)
  • Length: 88.7in (225cm)
  • Width: 30.8in (78cm)
  • Height: 40in (102cm)
  • Dry weight: 1,640lb (744kg)


  • Power output: * 1,290hp (962kW) at 3,000rpm at take-off.
  • 1,565hp (1,167kW) at 3,000rpm at 12,250ft (3,740m, MS gear)
    1,580hp (1,178kW) at 3,000rpm at 23,500ft (7,200m, FS gear)
  • Specific power: 0.96hp/cuin (43.6kW/L)
  • Compression ratio: 6:1
  • Fuel consumption: Minimum 39Impgal/h (177L/h), maximum 88Impgal/h (400L/h)
  • Power-to-weight ratio: 0.96hp/lb (1.58kW/kg) at maximum power.


  • Valvetrain: Overhead camshaft, two intake and two exhaust valves per cylinder, sodium-cooled exhaust valve stems.
  • Supercharger: Two-speed, two-stage. Boost pressure automatically linked to the throttle, coolant-air aftercooler between the second stage and the engine.
  • Fuel system: Twin-choke updraught Rolls-Royce/S.U. carburettor with automatic mixture control. Twin independent fuel pumps.
  • Fuel type: 100/130 Octane petrol.
  • Oil system: Dry sump with one pressure pump and two scavenge pumps.
  • Cooling system: 70% water and 30% ethylene glycol coolant mixture, pressurised. Supercharger intercooler system entirely separate from main cooling system.
  • Reduction gear: 0.42:1