History of aicraft piston engines

R o beriirsel and others w ere obsolescent by 1918

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Unformatted text preview: s, a l u m i n u m head, with hard valve-seat inserts, screwed o ver steel b a r r e l ; applied f i n n i n g on barrel is typical of many m o d e r n engines ( f r o m [ B r i t i s h ] A dvisory Committee for Aeronautics Report I.E.C. 260, p. 2 6 8 , f i g . 1 1 , J anuary 1919). 40 Air-Cooled Engines T he Gnome and its rotary descendants (LeRhone, Clerget, Bentley B. R., O beriirsel, and others) w ere obsolescent by 1918. Also obsolescent were air-cooled engines using cast-iron cylinders with integral heads and fins. T hese included the radial Anzani, and the Renault V-type with its descendants, the RAF (Royal Aircraft Factory), and FIAT. D uring the first World War it had become evident that the simple cast-iron cylinder 15 h ad reached its limit, and the Royal Aircraft Factory of Great Britain had employed Prof. A. H. Gibson, assisted by Samuel D. H eron, to develop more effective air-cooled cylinders. By 1918 they had c onstructed and tested steel cylinders with cast-aluminum heads screwed o nto them, that were capable of higher specific outputs than any cast-iron c ylinder (fig. 35, right). However, the practical use of the aluminum-head c ylinder in England was seriously delayed by a parallel development, s tarting in 1917, of air-cooled radials with steel flat-head cylinders capped by a b olted-on v alve-port assembly of cast-iron or cast aluminum (fig. 35, left). T his cylinder design suffered from the same trouble as the early H ispano-Suiza engines, namely, poor exhaust-valve cooling because of p oor contact between the head and the separate cooling element; however, t he first radial engine using this cylinder type, the ABC (All British Engine C ompany) Wasp of 4/^-in. b ore, was successful enough to gain the support of the British government for its development in a larger version, the Dragonfly of 5%-in. b ore. The fact that cooling problems increase with i ncreased cylinder size evidently was not realized at the time. T his development finally became, through several changes in ownership, t he Bristol Jupiter engine (fig. 37), which was built and used in c onsiderable quantities in England and in Europe, chiefly for military p urposes. It was never a really satisfactory aircraft engine, because of poor e xhaust-valve cooling (S. D. Heron said that its consumption should be given in terms of pounds of exhaust valves, rather than in pounds of fuel, p er horsepower-hour!). Finally realizing this fact, Bristol changed from steel heads to Aluminum heads with the Jupiter F, about 1930. M eanwhile the Gibson-Heron type cylinders had been further developed by Armstrong-Siddeley, and were used on the Jaguar 2-row r adial (fig. 38) which passed its type test in 1922, ten years after Gibson s tarted his work. A p arallel development of air-cooled engines with aluminum cylinders h aving steel liners was begun about 1916 by Charles L. Lawrance. Starting w ith a 2-cylinder opposed engine, he built a 3-cylinder engine in 1919, a nd 41 a vV, Figure 36.—Development of air-cooled cylinders in the United States: a, Lawrence J - l ( 1922) and Wright Aeronautical J-3 (1923) used cast aluminum structure with thin steel liner, b, Wright J-4 ( 1924) used flanged steel barrel with screwed-on head and jacket c asting, c, Wright J-4A (1924-5) s imilar to J-4. d, Wright J-4B (1925-6) similar to J-4A but with air passage and fins between the ports, e, Wright J-5 (1926-7) designed by Heron...
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