History of aicraft piston engines

F igure 6 0junkers j u m o 2 0 7 d 2 stroke cycle 6

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Unformatted text preview: veloped with the characteristics necessary for a truly successful full-scale aircraft engine. O n the other hand, nearly all engines used for model airplanes are 2-cycle and crankcase scavenged, for the sake of mechanical simplicity. I n 1966 an engine of this type became available for small target aircraft. T he Junkers diesel engine described above stands as the only 2-cycle aircraft engine ever to be used in considerable numbers for military and transport aircraft. F igure 6 0.—Junkers J u m o 2 0 7 - D 2 -stroke-cycle 6 -cylinder opposed-piston diesel engine (NASM 1 9 6 6 - 1 3 ) ; 1 200 hp at 3 0 0 0 r p m , 1430 lb. Photograph shows engine equipped w i t h exhaust-driven t urbo-supercharger as used in high-altitude German reconnaissance airplane in World War I I . E arlier unsupercharged versions (rated 7 5 0 hp at 1800 r p m , 1650 lb) were used in pre-war commercial airplanes. (Photo A-3112) F igure 6 1.—Napier L ion 12-cylinder W-type liquid-cooled engine, the only W-type ever widely u s e d ; 4 5 0 hp at 2 3 5 0 r p m , 985 lb. A racing version, of 8 0 0 hp, powered t h e 1927 winner of the Schneider T rophy, the Supermarine S-5 seaplane, which flew at 281.65 m p h . (Photo A-3098) F inally there should be m entioned some engines with unconventional cylinder a rrangements.-" T he first is the Napier Lion (fig. 61), the only W-type engine to see exten.sive service. This engine was liquid-cooled with its 12 c ylinders arranged in 3 rows of 4 each. Brought out in 1918, it was quite widely used in British m ilitary and commercial aircraft, and won the Schneider Trophy, a race for seaplanes, in 1927. A second engine in this category is the Pratt & W hitney R-4360, 28-cylinder air-cooled radial with 4 rows of 7 cylinders e ach (fig. 45). This is the largest (but not the most powerful) successful p iston-type aircraft engine ever to reach the service stage. It has been used in many large military aircraft and in the Boeing 377 Stratocruiser. Besides the large number of cylinders and their unusual arrangement in " staggered" r adial formation, unusual features include m achined-all-over c ylinder heads of novel shape and an ingenious arrangement of the pushrod valve gear. This engine would undoubtedly have been more fully developed had it not been for the advent of turbo-jet and turbo-prop engines. T he Rolls-Royce Eagle (the second line with that name) and the N apier Sabre, both using the double-crankshaft H arrangement, have a lready been mentioned (p. 57). U NCONVENTIONAL CYLINDER ARRANGEMENTS. 62 R elated Technical Developments F ully as important as the historical development of actual engines, has been progress in engine research, leading to improved understanding of the basic phenomena involved. Especial attention under this heading should b e given to the improvement in the structural design of aircraft engines m ade possible by the development of experimental stress analysis;21 h owever, a history of research in the field of internal-combustion engines is beyond t he scope of this paper....
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