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Aviation History
1947
1947 - 1081.PDF
FLIGHT July 3rd, 1947 3,500 h.p. RADIAL Pratt & Whitney WASP AAAJOR WORLD aircraft engine development at the begin-ing of the war was chiefly directed towards theproduction of more power both for military and commercial aircraft. The then key figure of 1,000 h.p. was only available from very few units and the most common layouts among the large designs had 9 or 14 cylinders radially arranged, or 12 liquid-cooled in vee form. After some eight years, designers of transports are still unable to get all the power they would like with- oi»t turning to gas turbines. An output of 3,000 h.p. or better from a large piston engine is still the exception rather than the rule. Because airscrew-driving turbines, having lost most of the simplicity of the pure jet unit, are unfortunately taking much longer to develop to a practical commercial stage than was ,at first optimistically estimated, and because, in America in particular, such units have not yet reached as advanced a stage of development as the British designs, a great deal of effort is still being con- centrated there on the design and development of very large piston engines. Even in this country there is evidence in commercial aircraft of a tendency to revert for a year or two more to/multi-cylinder pistpn engines in spite of their weight a^pd complexity. Quite recently the Rolls-Royce Eagle, with 24 cylinders arranged in H form, was announced. So far this largest British unit of 46 litres capacity, developing 3,500 h.p., has been applied only to one specific Naval aircraft. The power problem of the Bristol 167 Brabazon has been solved rather differently—namely, by coupling 18-cylinder radial Bristol Centaurus XXs in pairs, to produce, in effect, 5,650-h.p. units wteh a paired capacity of 107.2 litres. The largest aircraft piston engine, excluding the coupled type, to be built to date, is the American experimental 36-cylinder Lycoming XR.7755, designed to give 5,000 h.p. It is a radial arranged in four rows of nine cylinders each. A very interesting and promising example of the ex- ceptionally large American piston engine design is the 3,500 h.p. Pratt and Whitney Wasp Major, which is the power unit of such important new aircraft as the Globe- master, Constitution, Stratocruiser, XB-35 flying wing, six-engined XB-36, Mars flying boat, etc., Conceived in 1940, and actual design started in November of that year, the first unit was run in April, 1941. This extraordinarily short period indicates to some extent the tremendous resources of the Pratt and \^jhitney Company, but it was also made possible by the incorporation of many proved components from other Pratt and Whitney engines. About- one year later the Wasp Major flew, and a successful 150-hour type' test was completed in December, 1944, by which time the unit had 12,000 hours'- development running alone to its credit. The Wasp Major is a 28-cylinder air-cooled csdial arranged in four rows, each of seven cylindersy^These (Left) Many years of development have led to thlt heavily finned cylinder and head design. The Intake port Is between the rocker boxes in the top of the head. Right) Cooling airflow through four cylinders, com- prising one of the seven fore and oft banks: The air pressure drop required for cooling is said to compare favourably with that needed for two-row engines.
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