HARS Aviation Museum
HARS Aviation Museum

Rolls Royce Merlin Piston Aero Engine

RR Merlin

V12 piston aero engine

History of Type

A powerful, iconic, V12 supercharged, piston aero engine of ~1,650 cu inches (~27 L), first designed in the early 1930s by Rolls Royce to meet the Royal Air Force’s (RAF) need for a 1,000 bhp class aircraft motor.

Initially called the PV-12 (# Private Venture –12 cylinder as Rolls Royce funded the development costs) it was first bench test run in October 1933 and showed a modest ~750 bhp in its initial undeveloped form.

Interestingly, it was first test flown in an old fashion Hawker Hart bi-plane fighter in February 1935.  However, this was unsatisfactory so in 1936 Rolls Royce bought a Heinkel He 70, a German made high speed mail courier aircraft on which to test the PV-12.

The potential of the PV-12 was appreciated by the RAF which in 1935 issued a requirement for two new fighters to be designed around the PV-12.  These 2 new fighters became the famous Supermarine Spitfire and Hawker Hurricane.  At this point funding of the PV-12 was taken over by the British Government and the engine was given a new name – Merlin.  It is called Merlin after a small European hunting bird.

The Merlin was progressively refined and ultimately produced ~2,000 bhp in the 133 version.  It saw service in most British fighters (Spitfire & Hurricane) and bombers (Lancaster & Mosquito) of WW11, and some American aircraft like P51 Mustang.  It was also made by Packard in America where it was called the V-1650 or more commonly “Packard Merlin”.

History of HARS Engines

HARS’ engines are both Merlin 25s which powered the British built Mosquito bomber.  The first is #104605, built at Hillington, Glasgow on contract SB.4601 and delivered to the RAF on 25th July 1944.  The second #106607, was built by Ford at Trafford Park, Manchester on contract C/Eng/1480 and delivered to the RAF on 14th October 1944.

Technical Specifications

Engine Type: 12 cylinder, V-block piston engine, 1,650 cu in (~27 L), liquid cooled, supercharged

Manufactured: ~149,600 built in the period 1936-1950 in various locations, of which more than 55,500 were built by Packard in USA.

Usage: Fitted to many aircraft types, including:

  • Hawker Hurricane
  • Supermarine Spitfire
  • de Havilland Mosquito
  • Avro Lancaster
  • Handley Page Halifax
  • North American P51 Mustang