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Aviation History
1942
1942 - 2609.PDF
DECEMBER 17TH, 1942 FLIGHT 655 ROLLS- ROYCE MERLIN "SIXTY-ONE" NOTABLE BRITISH ENGINE PROGRESS : TWO-STAGE, TWO- SPEED SUPERCHARGER ENABLING STRATO- *•./ SPHERE FLIGHT By G. GEOFFREY SMITH, MM. FOGRESS in the design of superchargers, particu larly during the last three years, is responsible for aircraft engines of a given size developing far greater power at high altitudes. British technical achievement in this field is of the greatest importance in maintaining ascendancy over the enemy, and Rolls- Royce engineers are to be congratulated upon the intro duction into service types of the first proved type of two-stage two-speed supercharger. It is on operational duties in the Spitfire, and bears the type number "61." A month ago the existence of a new Spitfire fitted with the new type 61 Merlin engine was revealed, and brief details appeared in Flight of November 19th. This new Spitfire, which has two cannon and four machine guns, has already achieved striking successes in the air both over the Channel and in the Middle East theatre of war. One outstanding achievement was the destruction it a height of over 40,000ft. of three of Germany's stratosphere reconnaissance aircraft, type Ju 86P, which is reputed to have a pressure cabin, diesel engines and exhaust turbo superchargers. Since the heart of any good aircraft, be it fighter or bomber, is the engine, details now released for pub- Three-quarter rear view of engine. Features are the curved intake from twin-choke S U. carburettor to centre intake of first stage of supercharger, and the main duct from second stage of supercharger to intercooler. lication of the latest Rolls-Royce contribution to the many notable technical achievements of this world- renowned firm are of particular interest. The '' sixty- one" engine is a development of the twelve-cylinder V-type liquid-cooled Merlin, the perfection of which engine before the outbreak of war has meant so much to this country. The cylinder dimensions of 5.4m. bore by 6in. stroke, giving a capacity of 1,649 cubic inches, or 27 litres, re main the same; compression ratio is 6 to 1, but thanks to the development of a two-speed two-stage supercharger and an improved larger S.U. twin-choke carburettor, designed as a complete separate unit, the power output has been greatly increased, and the engine is capable of maintaining its exceptional performance over a far greater range than hitherto. Operational altitudes with the Spitfire-Merlin 6r combination in conjunction with a four-blade airscrew to absorb the greater power out put are now in excess of 40,000ft. Daily paper talk of air combats in the Battle of Britain at 40,000ft. was much exaggerated. Long years of experiment were necessary to bring the multi-stage supercharger and its necessary intercoo!-. fc#T< -*-i^SBW^Maii Three-quarter view of the improved Spitfire fitted with the R.-R. Merlin 61 engine and Rotol four-blade airscrew. LEADING PARTICULARS ! ROLLS-ROYCE MERLIN "61" i NUMBER or : CYLINDERS 12 ; BORE AND STROKE : VALVES—2 INLET ; 2 EXHAUST i COOLING MEDIUM 1 COMPRESSION • RATIO • SUPERCHARGER ... • CARBURETTOR j TOTAL CAPACITY. • i REDUCTION GEAR... • RATIO 1 DIRECTION OF : ROTATION • ESTIMATED NET • DRY WEIGHT ... Two monobloc castings of 6 j: cyKncLrs^ with detachable : heads. Cylinder banks se' • at 60°. 5.40" X 6.00". per cylinder operated by over- ; head camshafts via rocker?. Pressure water (30% glycol.) j 6.0: 1. Two-speed two-stage with • intercoolei. : S.U. twin-cholte updraught. ; 1.649 cu. ins. or 27 litres. Direct spur .42 :! Airscrew—right-hand Engine—left-hand ; 1,600 lb.+21%. ."
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