Manufacturing the Rolls-Royce Merlin XX
Part 1: Design and Production Details: Machining the Crankshaft and Camshaft,
Cylinder Liners and Connecting Rod
By J. A. Oates, A.M.I.E.I., Int.A.M.I.P.E.
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This article first appeared in the Volume 4, Number 42 (July, 1942) issue of Aircraft Production magazine, and is presented here through the kind permission of Flight International. Thanks also to Bruce Vander Mark for furnishing volumes of Aircraft Production for scanning. The Rolls-Royce Merlin XX 12-cylinder supercharged engine must rank as the most famous in-line engine in the world. It is applied to many leading types of British aircraft. This article by arrangement with the Ministry of Aircraft Production is the first of the series covering manufacture at one of the factories under the direct control of the engineers of Rolls-Royce, Ltd. As few major changes in design have been made for several years it has been possible to develop tooling and manufacturing methods far in advance of those normally encountered in the aircraft industry. Their success may be gauged from the fact that the percentage of skilled labour in this particular factory has been reduced to the amazingly low figure of 4.6, approximately 50% of the employees being women. |
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| The Merlin XX twelve-cylinder V-type liquid-cooled engine, the manufacture of which is described in the accompanying article, is one of the latest models of the famous range built by Rolls-Royce, Ltd. It has a two-speed supercharger. Compared with its predecessor, the Merlin X, the engine has a considerably improved performance both with regard to power output and altitude attainable. The maximum power available at 12,500ft altitude when using the low supercharger gear is 1,260 hp, whilst the high gear ratio produces 1,175 hp at 21,000ft. The engine weight is 1,450 lb. With a bore and stroke of 5.4” by 6.0”, the cubic capacity is 27 litres or 1,649 cu. in. An improved type of S.U. carburettor is fitted which reduces the effect of banking on the fuel level. | Fig. 1. A three-quarter front view of the 12-cylinder supercharged Rolls-Royce Merlin XX engine. |
Outstanding among liquid-cooled in-line engines of the present day is the Rolls-Royce Merlin XX (Fig. 1), fitted to many famous fighter and bomber aircraft. Compared with its predecessors the engine has been considerably stepped-up in performance, giving a maximum of 1,260 hp, at 12,250 feet when using the low supercharging gear. The total weight is 1,450 lb. The series XX engine has been developed from earlier types by a process of logical technical development based on service experience, and the increased power has been obtained without any major change in design. The cylinder dimensions still remain at 5.400” bore by 6.000” stroke, and the engine weight has been increased by only a very small amount. The adoption of a more efficient two-speed supercharger and the use of a larger carburettor are mainly responsible for the higher engine power output. A feature of the Merlin XX is its very small frontal area.
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