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Aviation History
1943
1943 - 0831.PDF
APRIL 1ST, 1943 FLIGHT 337 ENGINE PROGRESS 1918-43 REFLECTIONS UPON 25 YEARS OF AIRCRAFT ENGINE DEVELOPMENT : IMMENSE STRIDES DURING LIFE OF R.A.F. • By G. GEOFFREY SMITH, M.B.E. ElKING back over the 25 years' existence of the RoyalAir Force reveals the immense strides that have beenmade in the design and performance of aircraft power units. From every aspect, be it quality, volumetric effi- ciency, power output, specific weight per horse-power and, above all, reliability, progress has been so marked that to compare them with the simple types that were employed a quarter of a century ago is most impressive. Such has been the technical progress in aircraft engines over the past quarter of a century that it has only been possible in a brief space to compare • their general features. From simple two- valve engines largely de- veloped from racing cat- practice and weighing 3 lb. per h.p., to-day much larger four-valve engines of com- plex construction, and mount- ing drives for the variou; auxiliaries on modern aircraft, develop around 1 h.p. perlb. In 1918 the engine produced in greatest numbers was the Siddeley Puma, which developed 240 h.p. at 1,400 r.p.m. It was a naturally aspirated six-cylinder water- cooled vertical in-line unit with two exhaust and one inlet valve per cylinder, simple in design, with a direct-drive airscrew. It took only about 1,380 man-hours,to produce, according to records of that time, and cost about ^900. A modern supercharged engine with 12, 18 or 24 cylinders, far and away more complex in its equipment, costs some £3,000 and occupies fully 3,000 man-hours in production by the most modern machine tools and factory technique. After a wonderful career, rotary radial engines were TO attempt to review in brief space the broad subject of aircraft engine development over 25 years is ambitious, and in a way unsatisfactory, as so much must remain un- chronicled. In this summary of the trend of design the writer, who was a captain in the R.A.F. engaged upon engines in the last war, touches upon the salient changes and quotes a number of informative comparisons. becoming outmoded, but there were several notable examples even in 1918, including the Clerget manufactured by Gwynnes and the BR 2 made by Humber, Ltd., and developed by W. O. Bentley, now designer for Lagonda Motors. Also considerable numbers of the Gnome Monosoupape engine still existed. As the name implies, this engine had only one valve per cylinder ; this was the exhaust valve, located in the head. Air was admitted via the hollow stationary crankshaft and mixed with iuel injected from a nozzle into the crankcase. Ports cast in the skirt of the cylinder pro- jecting into the crankcase were uncovered by the piston at the bottom of the stroke, so admitting mixture to the cylinder. A favourite engine of the time was the fiii?<?;' cylinder Le Rhone rotary, developing some 80 b.h p. and weighing 258 lb. Engines of V type were being favoured for their com- pactness. Among the notable water-cooled examples were the comparatively new Rolls-Royce 360 h.p. Eagle twelve- cylinder engine (with two valves per cylinder), the 212 h.p. eight-cylinder Sunbeam Arab (two exhaust and one inlet per cylinder), and the 180 h.p. .eight-cylinder 90 (leg. Hispano Suiza (two valves per cylinder), known as the Wolseley Viper, produced by Wolseleys, of Birmingham. In common use was the R.A.F. V-type eight-cylinder air- cooled engine on the same general lines as the Renault. At that period, too, Napiers were manufacturing the Arab, and gradually transferring their energies to the 450 h.p. twelve- cylinder three-row (broad arrow) Lion. This engine, j ARMSTRONG SIDDELEYHIGH SPOTS : Top row (left), Seven-cylinder Lynx, 150 h.p, in1922, 235 h.p. in 1929. (Centre) Fourteen-cylinder Jaguar, 300h.p. in 1922, 500 h.p. in 1929- (Right) The 340 h.p. Cheetah Xfitted to the Oxfords and Alisons. At the bottom is a productionstore of 240 h.p. Pumas in 1918.
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