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Aviation History
1966
1966 - 1400.PDF
ft/GHT International, 12 May 1966 797 A 25th Anniversary and its Implications Whittle's 8S0lb-thrust W.I centrifugal turbojet and one of its leading descendants,T_Jhe 8,S00lb-thrust Pratt & Whitney J48 of nearly a decade later " The 1,230 s.h.p. Rolls-Royce Trent (top), the world's first turboprop to fly, and the Rolls- Royce Tyne, which generated over four times the power and represented the ultimate in turboprop technology WHEN the Gloster E28/39 made its historic first flight onMay 15, 1941, it was powered by an 8501b-thrustWhittle W.I centrifugal turbojet intended to give the aircraft a top speed of around 338 m.p.h. Specific fuel con- sumption was 1.41b/lb/hr, and the engine weighed 6231b, equivalent to a thrust:weight ratio of 1.36:1. With the excep- tion of the s.f.c, how almost insignificant these figures appear today, and how virtually impossible it must have been then to foresee what would stem from this small beginning. German axial technology, although well advanced by the end of the war, was eventually dispersed to France, Russia and the United States. It consequently failed to measure up to the profound impact of Whittle's centrifugal work, which became the direct source of technology for Rolls-Royce, General Electric, and de Havilland. The centrifugal engines of these companies were in turn manufactured by Pratt & Whitney, Hispano-Suiza, Fabrique Nationale, Rolls-Royce of Canada, Klimov and other Russian design bureaux, Allison, Flygmotor, Fiat and Sulzer. Almost the entire first-round of turbine- powered military aircraft, West and East, derived their success from Wittle and his Power Jets team. The main stream of turbine development in the early post- war years continued to be the single-shaft, single-stage centri- fugal turbojet. The Rolls-Royce Derwent powering the Gloster Meteor was instrumental in establishing the first world air speed record by a jet aircraft, and the de Havilland Ghost powering the Comet became the world's first turbine to enter airline operation. An intensive research effort had, however, been initiated during the closing years of the war to secure early introduc- tion of the axial compressor. This mode of compression offered easier multi-staging and hence higher pressure ratios, leading in turn to reduced s.f.c. Diameter was also smaller. In Britain, stemming in large measure from compressor work at the RAE and NGTE, the Rolls-Royce Avon and Armstrong Siddeley Sapphire axial turbojets (the latter engine of Metro- Politan-Vickers origin) came into being. Even earlier, in the United States, the Allison J35 and General Electric J47 were produced in many tens of thousands. These early axials were all single-shaft designs, and they enabled engine pressure ratio to be raised from 4.5:1 to around 6 or 7:1. Through indigenous and licensed manufacture they were built in considerable numbers around the world, rnore so than any other basic category of turbine to date—a distinction they are likely to retain for many years to come. Their development was accompanied almost simultaneously °y that of the twin-spool axial turbojet, in particular the Pratt & Whitney J57, over 21,000 of which were built, and the Bristol Olympus. These engines had an initial pressure ratio of around9; 1. and in their early versions were rated at 10,0001b, a thrust somewhat higher than that of their single-shaft contemporaries, 'he J57, coupled with a sophisticated afterburner, powered the USAF's first supersonic fighters, and in JT3 civil form it pro- vided the power unit for the Boeing 707 and Douglas DC-8 as America's first entries in the jet transport field. General Electric, who had built some 40,000 J47s, sought to retain the advantages of the single-shaft axial and developed a unique family of compressors incorporating variable incidence stator blades. This type of compressor has been used in all the company's succeeding engines, including the J79 turbojet, GE's rival to the J57. In a third and even more fundamental reappraisal of the jet propulsion scene, Rolls-Royce in 1952 started development of the Conway, the world's first practical turbofan. Launched initially in military form, the Conway was also ordered by BOAC and other international operators for their 707 and DC-8 aircraft Here its s.f.c, markedly lower than that of the turbojet, presented a major threat to Pratt & Whitney's early domination of the big civil jet market and the American company quickly and very effectively adapted the JT3 to a front-fan configuration. General Electric strengthened its bid for civil transport business by introducing an aft fan on its CJ-803 single-shaft turbojet. Final major development in military turbojet technology was the emergence of the big supersonic single-shaft axial of moderate pressure ratio for propulsion at high Mach numbers. Earliest of these was the de Havilland Gyron, followed by the Pratt & Whitney J58 and General Electric J93. The American engines were among the first to power aircraft at Mach 3. They represent some of the last examples of the turbojet whose place in the main stream of turbine development has been pro- gressively assumed by the turbofan. Two other basic lines of turbine development have taken place, first with the turboprop and then later also with the turboshaft. Outstanding by its international success is the centrifugal single-shaft Rolls-Royce Dart turboprop, first developed at the end of the war and today still in large-scale production. It was this engine, powering the Vickers Viscount, that in 1954 attained the distinction of being the world's first turboprop to enter airline service. All other turboprops of note have been axial, ranging from the free turbine Bristol Proteus (having an additional centri- fugal stage), through the single-shaft Allison T56/Model 501 to the twin-spool Rolls-Royce Tyne. Significant by its massive power is the 15,000 s.h.p. Kuznetsov NK-12 powering the Antonov An-22. Largely because of the turboprop's added complexity and competition from the turbofan, total produc- tion of this type of engine has not been of a similar magnitude as that of its jet contemporaries. Major turboprop activity today is limited to the 300 h.p. to 900 h.p. category with such engines as the Turbomeca Astazou, AiResearch TPE331/T76 and P&W PT6-A/T74. Prime contribution of the turboshaft engine has been to helicopter propulsion where the high power, small size and low weight of the turbine have provided marked gains over the piston engine. Pioneering contributions to this sector have been
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