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Revision as of 10:09, 19 June 2002 by Maury Markowitz (talk | contribs)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)The Merlin is an aircraft engine built in WWII by Rolls Royce. It was one of the best engines in the world, and powered many of the greatest planes of the war.
Prior to the war Rolls had been planning to have two main engines through the late 1930's and into the 1940's. The 700hp Peregrine was a updated development of the earlier V-12 Kestral which had been used to great success in a number of 1930's designs. Two Peregrine's bolted into an X-24 would create the 1,700hp Vulture, for use in larger planes like bombers. There was also the possibility that the famous R engine from the Supermarine racing planes could be developed into a 1,500hp class engine of its own, itself a development of the Buzzard, a scaled up Kestral.
However this plan left a large gap between 700hp and 1,500hp. To fill the gap work was started on a new 1,100hp class design as the PV-12 -- PV for "private venture" as they received no money for work on the project. It first flew on the front of a Hawker Hart biplane in 1935, using the new evaporative cooling system then in vogue. This system proved to be somewhat suspect, and when supplies of Ethylene Glycol (Prestone) from the US became available, the engine was switched to this system instead.
The next year the fighter competition resulted in two planes utterly dependant on supplies of the PV-12, namely the Hawker Hurricane and Supermarine Spitfire. With no other modern fighters on the drawing boards, the PV-12 was catapulted to the top of the supply chain and became the Merlin. First widely delivered as the 1,030hp Merlin II, the 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 England's captipulation.
Early Merlins were considered to be rather unreliable, but their importance was too great for this to be left alone. Rolls introduced a quality control program to address this, which consisted of taking random engines right off the assembly line and running them continously at full power until they broke. They were then disassembled to find out what part failed, and that part was redesigned to be stronger. After over a year of this the Merlin matured into one of the most reliable engines in the world, allowing themselves to run at full power for entire eight hour bombing missions without complaint.
As it turns out the Peregrine saw use in only one plane, the Westland Whirlwind. Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature as Rolls spent all of their time troubleshooting the Merlin. Likewise the Vulture was used in the superlative Hawker Tornado and Avro Manchester, but proved to be completely unreliable. With higher power gasolines available from the US the Merlin was soon pushing into the 1,500hp range on its own, and both engines were cancelled in 1943.
Most of the upgrades to the Merlin were the result of ever-increasing octane ratings in the aviation fuel available from the US. At the start of the war the engine ran on the then-standard 87 octane avgas and could supply just over 1,000hp from it's 27l displacement (compared to 1,100hp from the 34l DB 601).
The next major version was the XX which ran on 100 octane fuel. This allowed it to be run at higher compressions, which they achieved by increasing the "boost" from the supercharger. The result was the otherwise similar engine delivering 1,300hp.
which allowed it to be "boosted" to higher levels by its supercharger and the otherwise similar engine could now deliver 1,300hp. Another boost in octane and a new two-stage supercharger resulted in the
It could be said that the old myth that Merlin would return to save Britain at its time of greatest need was proved correct. Strictly speaking, however, the Merlin name came from the sea bird rather than King Arthur's legendary magician.
Links:
The Rolls Royce Merlin and Griffon aeroengines, a description.