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Aviation History
1954
1954 - 1297.PDF
578 FLIGHT, 7 May 1954 THE TWO Rs . . . also made to the rotating and fixed guide vanes and the improve ments mentioned, in conjunction with a larger, twin-choke, up- draught S.U. carburettor (designed as a complete, separate unit), gave a marked increase in power. Thus, using 100-octane fuel, the international rating in low gear was 1,240 h.p. at 2,850 r.p.m. at 10,000ft and plus 9 lb/sq in boost; in high gear the figure was 1,175 h.p. at 2,850 r.p.m. at 17,500ft, again at plus 9 lb boost. Flight commented: "These figures represent an increase of nearly 250 h.p. over the Merlin II of identical cylinder dimensions, and illustrate in a convincing manner the technical progress achieved by years of 'toil, tears and sweat,' to borrow a classical phrase from our worthy Prime Minister. Nor is the limit of attainment yet in sight." It was further remarked that the achievement of extracting so much extra power from a given cubic capacity had increased the dry weight by only 75 lb, and that over 100 h.p. were being taken from each cylinder. The Merlin XX powered the Beaufighter II, Defiant II, Halifax II and V, Hurri cane II and IV, and Lancaster I and III. Merlins 21, 22, 23, 24 and 25 were all essentially similar to the Merlin XX. The 21 was fitted in the Mosquito I, II, III, IV and VI; the 22 in the Lancaster I and II and the York I; the 23 in the Mosquito I, II, IV, VI, XII and XIII; the 24 in the Lancaster I and III and York I; and the 25 in the Mosquito VI and XIX. Take-off power of the 24 and 25 was 1,620 h.p. The Merlin 28 was a Packard-built engine, installed in the Lancaster I and III and the Kittyhawk II and known in America as the V-1650-1. When it was disclosed in Great Britain that this American-built engine would differ from its British equivalent in having detachable cylinder heads, it was explained that this form of construction had already been proved satisfactory by Rolls-Royce, Ltd., and would have been adopted by them two years or more previous to the Packard innovation had it not been for the fact that such an important modification would have delayed the attainment of maximum production. The Merlin 29 was also Packard-built, but had a reduction gear ratio of 0.477 : 1 instead of 0.42 : 1, and was fitted with a splined airscrew shaft; it was fitted in Canadian-built Hurricanes and the Kittyhawk II. Changes from its predecessor were so small that the designation V-1650-1 was retained. The Merlin 30 was a medium-supercharged engine, installed in the Barracuda I and Fulmar II, and giving 1,240 h.p. at 7,250ft and a take-off output of 1,300 h.p. The Merlin 31 was another Packard V-1650-1 and was mounted in the Canadian Mosquito XX, the Australian Mosquito 40, and the Kittyhawk II. An increase in take-off output from 1,300 h.p. to 1,600 h.p. charac terized the Merlin 32, which powered the Barracuda II and Seafire II. The Merlin 33 was yet another Packard-built version, installed in the Mosquito XX and 40, and the 38 (also by Packard) was fitted in the Lancaster I and III. Both the 33 and 38 gave 1,390 h.p. for take-off. A variant which saw very extensive service was the Merlin 45, fitted in the Spitfire V, P.R.IV and VII, and Seafire II; at 16,000ft and 2,850 r.p.m. its output was 1,200 h.p. The Merlin 45M was rated for duty at lower levels and delivered 1,585 h.p. at 2,750ft; it was fitted in the Spitfire L.F.V, The Merlin 46 and 47 were both high-altitude engines (1,115 h.p. at 19,000ft); the 46 powered the Spitfire V, P.R.IV and VII, and Seafire I, and the 47 (which had a cabin supercharger) found its application in the Spitfire VI. The Merlin 50 was similar to the 45 and was fitted in the Spitfire V; the 50M was almost identical with the 45M and powered the Spitfire L.F.V; the 55 was again like the Merlin 45 and was fitted in the Spitfire V and Seafire III; and the 55M resembled the 45M and was the power unit of the Spitfire L.F.V and Seafire L.F.III. In March 1940 Rolls-Royce had been asked by the Ministry of Aircraft Production to submit their proposals for increasing the high-altitude output of the Merlin to enable a pressurized develop ment of the Wellington to operate at 40,000ft. An output of 800 h.p. at 40,000ft was estimated to be required. To that end the company set about experimenting with a two-stage supercharger, and an engine with this fitment was bench-tested in April 1941. This became the Merlin 60, which, though installed in Wellington Vis, was soon declared obsolete. Adapted for fighter requirements, however, and designated Merlin 61, the new engine was installed in the Spitfire VII, VIII, IX, and P.R.XI, and gave those fighters a decided "edge" over their German adversaries. The key feature of the Merlin 61 was its two-speed, two-stage supercharger, with two rotors on a common shaft. The mixture was compressed by the first stage and was delivered to the inlet of the second stage, where it was further compressed before being delivered to the induction pipe. In order to reduce the mixture temperature to a normal figure, a box-like intercooler was inter posed between the outlet of the second-stage supercharger and the rear of the cylinder blocks. In a typical Spitfire installation the intercooler radiator was mounted under the port wing in a duct, which also housed one of the main engine-cooling radiators. The real significance of the Merlin 61 was that at 40,000ft it developed double the power given at a much lower altitude by the Merlin II of 1939/40. Even at 23,500ft its maximum power was 1,390 h.p. The weight had risen to 1,640 lb. The Merlin 62 was used in the Wellington VI, and the 63 (wherein the maximum output had risen to over 1,650 h.p.) appeared in the Spitfire VII, VIII, IX and P.R.XI. The 64 was similar to the 63 but had a cabin supercharger; it was mounted in the Spitfire VII. The 66 powered the Spitfire L.F.VIII and IX. The 67 had a reduction gear of 0.42:1 instead of 0.477:1, as had the 63, 64 and 66, and the 68 was a Packard-built model, designated V-1650-3 and installed in the Mustang III. Its take off output was 1,400 h.p. In the Merlin 69—another Packard- built variant, known in America as the V-1650-7—1,490 h.p. was available for take-off; this engine powered Mustang Ills and IVs. The Merlin 70 appeared in the Spitfire H.F.VIII and IX and P.R.XI, and the 71 (with cabin blower) in the Spitfire H.F.VII. The Merlin 72 was applied to the Mosquito P.R.IX, XVI and 30, and the Westland Welkin I. Some Mosquito XVIs and Welkin Is had Merlin 73s or 76s. The 76 was the same as the 72, but had a cabin supercharger. Yet another engine for the Mosquito XVI and Welkin I was the 77, with cabin supercharger. In the Merlin 85 the take-off output was increased to 1,635 h.p. This was a bomber engine and was installed in the Lancaster VI and Lincoln I. The Merlin 224 was built by Packard and was the same as the Merlin 24; it was fitted in the Lancaster I and III. The 225 was another Packard-built model used in the Mosquito 25 and 26 and identical with the Merlin 25. The Merlin 266—again Packard-built—was the same as the Merlin 66 and was mounted in the Spitfire L.F.XVI. The war being over, and the exigencies of security less restric tive, particulars were released of the Merlin 113 and 114, which became well known as the power plants of Mosquitoes 34, 35 and 36. These engines delivered 1,430 h.p. at 27,250ft with a boost pressure of plus 18 lb. Even more notable were the Merlin 130 and 131, specially "tailored" for the de Havilland Hornet. The installation of these was amazingly clean, and in this con nection it may be observed that a steady increase in b.h.p./sq ft of frontal area had been achieved by Rolls-Royce since the days of the Eagle and Falcon. Thus, every four years between the two World Wars an increment of roughly 25 b.h.p./sq ft was attained until 1936. With the advent of the Merlin there was a very decided improvement, amounting to 60 b.h.p./sq ft, continuing until 1940. Between 1940 and 1944 the figure was 100 b.h.p., and in 1945, with the introduction of the Merlin "100" series, 340 b.h.p./sq ft was recorded. The Merlin 130 and 131 were the first of their family to incor porate downdraught carburettors; and, to eliminate the air scoop as used on the Mosquito, ducted air intakes were faired into the leading edges of the wing. The war-time Bendix/Stromberg carburettor was replaced by a low-pressure fuel-injection system, which delivered through a spray nozzle into the supercharger eye. The 130/131 differed, incidentally, only in being "handed" right and left respectively. The sum total of improvements incorporated in these remarkable engines raised the output to 2,030 h.p. at 1,250ft with a boost of plus 25 lb/sq in. Another special military Merlin of the post-war years was the 140, developed for the Short Sturgeon and equipped to drive contra-rotating airscrews. Emergency maximum power was 1,650 h.p. at 16,750ft. As though the foregoing mass of engine designations were not sufficiently bewildering, we now have to record that the latest Merlin to go into service with the R.A.F. and Royal Navy is the 35, a trainer engine developed for the Avro Athena and Boulton Paul Balliol. It has a single-speed supercharger and a maximum take-off output of 1,280 h.p. Although the Merlin engine will be remembered principally for its military applications, it has achieved in post-war years a
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