| Continued from above… to be rather unreliable. As a result, Rolls-Royce introduced an ambitious reliability-improvement program to fix the problems. This consisted of taking random engines from the end of assembly line and running them continuously at full power until they failed. Each was then dismantled to find out which part had failed, and that part was redesigned to be stronger. After two years of this program the Merlin had matured into one of the most reliable aero engines in the world, and could sustain eight-hour combat missions with no problems. A particular problem with Merlin I was its ?ramp head? where the inlet valves were at a 45-degree angle to the cylinder. This solution was not a success and was replaced with Kestrel-style conventional flat head arrangement wherein the valves are parallel to the cylinder. This modification was designated Merlin II. Rolls-Royce Merlin... Made world famous for powering many of the most legendary aircraft... Mustang, Spitfire, Hurricane, Mosquito, Lancaster etc...
The early Merlins were used by the British Royal Air Force in the Hawker Hurricane and Supermarine Spitfire. Their success led to these supercharged versions that offered even higher performance, and at higher altitudes.
In 1940, the Packard Motor Car Company of Warren, Ohio (USA) negotiated a licensing agreement with Rolls Royce to produce their Merlin aircraft engines. The marriage of the North American P-51 Mustang airframe and the Packard Merlin engine, in 1942, created the most successful fighter aircraft of World War II. Long-range Merlin-powered P-51s escorted Allied bombers and helped the Allies achieve complete air superiority in Europe by mid-1944.
Most of the upgrades to the Merlin engine were the result of ever-increasing octane ratings in the aviation fuel available from the US, and ever more efficient supercharger designs. At the start of the war the engine ran on the then-standard 87 octane aviation spirit and could supply just over 1,000hp from its 27 litre displacement (compared to 1,100hp from the 34 litre DB 601).
The next major version was the Merlin-XX which ran on 100 octane fuel. This allowed it to be run at higher compressions, which was achieved by increasing the "boost" from the supercharger. The result was that the otherwise similar engine delivered 1,300hp. This process continued, with later versions running on ever-increasing octane ratings, delivering ever-increasing power ratings. By the end of the war the "little" engine was delivering over 1,600hp in common versions, and could deliver over 2,000hp for brief periods in some versions.
The Merlin engine was considered to be so important to the war effort that blueprints were sent to the US for safekeeping, to be handed over in case of the UK's capitulation. When this was no longer an issue in 1943, the Packard company started production in the US as the V-1650, originally for use in US-built Spitfires. The V-1650 was so much better than its US counterpart (the Allison V-1710) that it would replace that engine in the P-51 Mustang, which then went to become one of the best fighters of the war.
In comparison the Luftwaffe had no similar ability to increase octane ratings, and had to continually introduce larger and larger engines to keep up. The result was that their planes had considerably worse power-to-weight ratios than the Merlin powered planes they faced, and the continual complete change in engines designs meant they never had enough to go around. The lack of engines was one of the major problems for the Luftwaffe, from the mid 1930's right until the end of the war.
For this reason the "Merlin engine" is often considered to be one of the main factors in winning the war for the Allies. As the Merlin evolved so too did the supercharger; fitting into three broad categories:
- Single-stage, single-speed gearbox: Merlin I to III, XII, 30, 40, and 50 series
- Single-stage, two-speed gearbox: Merlin X, Merlin XX
- Two-stage, two-speed gearbox with intercooler: mainly Merlin 60, 70, and 80 series
Most of the Merlin's technical improvements resulted from more efficient superchargers and fuel with increased octane ratings. Debs McCaffrey |
