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Aviation History
1939
1939 - 0681.PDF
MARCH 9, 1939 FLIGHT. 243 The development of the Bristol cylinder with every picture telling a story—a '0lL<^ story of greater power, higher speeds, greater fin area. about 40,000ft., it enabled the engine to develop its maxi- mum r.p.m. at 42,000ft. In 1937 the first commercial trans atlantic crossings by air were made by two of Imperial Air- ways Pegasus- engined Empire fly ing boats. One jour ney was completed in 10 hours 36 minutes, at an average speed of 191 m.p.h. Another event of the same year which must be recorded as the outcome of much research and development work by the Bristol Company was the formation of Rotol Airscrews, Ltd., representing the joint interests of Rolls-Royce, Ltd., and the Bristol Company, for the manufacture of constant- speed controllable-pitch airscrews. As long ago as 1926 the Bristol Company had designed rue manufactured air screws with forged duralumin blades secured in steel hubs. From 1931 onwards the Company, in collaboration with the Gloster Aircraft Company, Ltd., tested the Hele-Shaw con stant-speed airscrew fitted to the Jupiter engine of a Gloster Gamecock fighter. Three years later the company under took the development of this design for the Air Ministry, and in 1936 Bristol constant-speed three-bladed airscrews were type-tested and approved for Pegasus and Mercury engines respectively. Rotol airscrews are now being manu factured in a special factory near Gloucester. Latest Types Returning to engines, the latest additions to the Bristol poppet-valve range include the 890 h.p. Mercury X, XI and XII (the last-named being fitted in the first batches of the Westland Lysander army co-operation machines) ; the Pegasus XXII, with a take-off power of over 1,000 h.p. ; and the Pegasus XVIII series fitted with a two-speed super charger. This latter device, of course, combines the high take-off power of a moderately supercharged engine with maximum performance at high altitude. The Bristol two- speed blower embodies triple, balanced, double-acting clutch units, hydraulically operated, enabling the Pegasus engine to develop 1,000 h.p. at 3,000ft. and 885 h.p. at 15,500ft., as well as the excellent take-off output of 960 h.p. Fresh splendour was added to the record of the Pegasus when three Vickers Wellesleys, fitted with engines of this type, flew last year from Egypt to Australia, two of them covering Ismailia-Darwin non-stop. Actually, the engines used were of the Pegasus XXII type, operating on 100-octane fuel. Before tracing the development of the Bristol sleeve-valve aero engine, which is believed by many to be the greatest contribution yet made to the problem of power for aircraft, W<J rnay record the projection and development of certain other types of aero engines. Twelve years ago a design was Prepared for 1,000 h.p. eleven-cylinder radial of 7fin. bore and 12m. stroke, operating on oil fuel. A single-cylinder unit was built, and after a good deal of research a nine- cylinder compression-ignition engine similar in size to the gasus was Produced and tested in February, 1932. This engine, known as the Phoenix, developed 485 h.p. at 2,000 •P-m. on a standard grade of crude-oil fuel of about 0.85 jT^ gravity. In May, 1934, a Phomix, fitted in a West Wapiti bipane, gained the world's altitude record for mpression-ignition engines by reaching a height of enri > ^e SUDsecluent development oi this type of the A vr been delaVed by the military requirements of r Mlr»stry for high-powered petrol engines. It was in 1927 that the first single- and two-cylinder research was undertaken into the possibilities of the single- sleeve-valve principle. The work received the assistance of the British Air Ministry, and the first research unit was an inverted vee twin of 5fin. bore and 6in. stroke, intended to represent a section of a possible inverted twelve-cylinder engine. For five years this research went on. One of the results, with which the company experimented for two years, was a six-cylinder sleeve-valve unit of 4£in. bore and 4^in. stroke intended for a possible vee-twelve engine. Eventually, however, the designer returned to the radial type as promising the best solution for high power. A nine- cylinder sleeve-valve engine of the same size as the Mercury (capacity 1,520 cu. in.) was built, and in 1932 this unit, known as the Perseus, completed the first 100-hour British Air Ministry Service type test, being rated at 580 h.p. at 2,300 r.p.m. In 1933 research work began on a sleeve-valve cylinder of 5in. bore and 5fin. stroke, and in the following year this was applied to a nine-cylinder engine of 950 cu. in. capa city which passed its type test as the Aquila with an output of 500 h.p. at 2,600 r.p.m. This research work on the small cylinder was doubly important, as it led, some five years later, to the produc tion of the Taurus 14-cylinder two-row radial of only 46Jin. diameter, which passed its type test in 1938, being rated at 1,065 h.p. and 3,225 r.p.m. This is claimed to repre sent the summit of achievement in power-for-weight yet attained in high-output aero engine design. Perseus Developments Returning to the year 1936 we find the Perseus engine being further developed, and the Perseus VIII type tested at 810 h.p. This was the first sleeve-valve engine to be adopted by the R.A.F., No. 42 Squadron, equipped with Vickers Vildebeest torpedo bombers, using it with highly satisfactory results. Imperial Airways had already fitted the Perseus II in certain of their machines, and it became extremely popular for the small amount of maintenance required, its satisfactory running and its economy. Also in 1936 the Bristol Company produced its first double-row radial engine—the fourteen-cylinder Hercules, using Perseus-type cylinders. This was Britain's most powerful type-tested aero engine, being rated at 1,375 h.p. at 2,750 r.p.m. The Hercules has been selected for instal lation in the new large flying boats for Imperial Airways. Two years ago sleeve-valve engines went into full quan tity production, the first types scheduled being the Perseus X, XI and XII. The Series X is a fully super charged engine delivering 880 h.p. at 15,000ft. with a bare dry weight of only 1,085 lb. The series XI and XII are moderately supercharged units delivering 905 h.p at 6,500ft. The civil-rated Perseus, designated the XIIC, has already been installed in three types of commercial aircraft. This has a take-off power of 890 h.p. at : 2,700 r.p.m., developing 815 h.p. at 2,600 r.p.m. at 1 6,000ft.
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