Rolls-Royce Merlin engines

The Rolls-Royce Merlin, a British built engine, was developed in various steps. In the 1920's, Rolls-Royce oversaw the development of the 'R' engine, which evolved from both the Kestral and then Buzzard (Rolls-Royce utilized names of birds for their engines) to spur Britain's entry into the International Schneider Trophy seaplane contest. In 1931, the engine set a new world's speed record of over 400mph over water, and then over land. More importantly, as later events were about to prove, this design experience gave Rolls-Royce the technological basis to develop the Merlin.

By 1932, it was obvious that the 745hp "Kestrel" engine, that had thus far been a bestseller, was coming to the end of its developmental life. Sir Henry Royce, about one year before his death in 1933, made a decision to develop a new engine using some of the experience of the Schneider Trophy winning 'R' engine. This new engine was initially known as the PV12 (private venture), and was entirely funded by Rolls-Royce up to that point. However, in 1933, the British Air Ministry agreed to finance the development of this engine, which was then termed the "Merlin."

In 1940, when Britain was at her knees in an air war with Germany, that determined whether Germany would invade, the mighty Merlin powered the Spitfires and Hurricanes in the "Battle of Britain" that thwarted the enemy's attempt. Being in strong need of aircraft, Britain employed America to build her a plane. The P-40 was requested, but production wasn't adequate, so James H. "Dutch" Kindleberger of North American Aviation, built the all-new P-51A, powered by an Allison. After limited success due to limited altitude, the P-51B received the V-1650-3 Merlin, and subsequent models (P-51C-K) received the V-1650-7 model.

Ironically enough, in spite of its later reputation of extreme performance, the project was riddled with problems. After many developments, which entail the A-G Merlins, the G model, which was termed "Merlin II," became a successful engine after having had passed testing. This Merlin II, with modification for high output, notably attempted a speed record in 1937, while installed in a Supermarine Spitfire.

In 1935, after many difficulties with the supercharger gearing (supercharger being mechanically driven while a turbocharger is exhaust driven), Rolls-Royce took out a license to utilize the Farman two-speed drive. Sir Stanley Hooker, a mathematician, then developed this system to increase performance at higher altitudes. This version became known as the Merlin XX and was used in the British Beaufighter, Defiant, Halifax, Hurricane, Lancaster planes and others.

Further development produced the first American built Merlin (done under license by the Packard Motorcar Company of Detroit), the V-1650-1, which was used in the P-40F model. P-40's had used the dependable Allison engine that utilized a turbocharger, however, GE could not meet production demands of equipping both bombers and fighters with turbochargers, so most Allison powered planes were limited by altitude. Such was the case with most P-40's, and the initial P-51A.

The idea of a marriage of the P-51 mustang airframe and the Rolls Royce Merlin engine began long before anyone had ever heard of a Mustang. And, contrary to popular belief, this was not exclusively a British idea. Why the Merlin? The answer to that question is simple expediency! The Rolls Royce Merlin engine was a proven design and available at the time. It was already powering some of the world's best warplanes - the Hurricane, Avro Lancaster and, of course, the superb Supermarine Spitfire.

To develop a new engine for the P-51 comparable to the Merlin required time, time the Allies simply did not have. Remember this was mid-1942 and the United States was still reeling from the Pearl Harbor attack, Great Britain was still standing alone opposite an entirely hostile continent and Soviet Russia was still retreating before the Nazi Blitzkrieg. The Allies needed weapons to fight the tide of defeat and they needed them right away! One of those weapons would be the Merlin-powered Mustang.

The mighty Merlin, with its extremely good supercharger, gave the Mustang the ability to perform well up to 41,900 feet achieving the speed of 437mph. This combination of engine and plane, produced the winning superior allied fighter of WWII.

During the war there was enormous pressure to develop the capacity of the piston engine. The Merlin typified the trend, more than doubling in power from 746 kW (1000 hp) in 1939 to over 1567 kW (2100 hp) by 1944, mainly through improvements in supercharging.