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Aviation History
1966
1966 - 1401.PDF
798 RIGHT International, 12 May 1966 The 6,500lb-thrust Rolls-Royce Avon RAJ (top) Britain's first axial to enter service, and America's latest 30,0OQIb-thrust Pratt & Whitney J58 powering the Mach 3 Lockheed F-I2A intercepts The Rolls-Royce RB.I62 16:1 thrust:weight ratio lift jet (top), cornerstone of Rolls-Royce V/STOL composite propulsion concept, and the contrasting Bristol Siddeley BS.IOO vectored- thrust turbofan with plenum chamber burning The S,0OOIb-thrust de Havilland Ghost turbo- jet, (top), the world's first turbine to enter air- line operation, and the mighty Olympus 593 A 25th ANNIVERSARY . . . made by Lycoming with the T53 and T55, Turbomeca with the Turmo and Artouste, General Electric with the T58 and T64 and Napier with the Gazelle. Today—25 years, almost to a day—after the Whittle W.I first flew, turbine technology is far from having reached a plateau; it is burgeoning as never before. In three fields alone —SST, V/STOL and ultra-heavy transport propulsion—new configurations of engine are being evolved. Intriguingly, the four engines being developed for the three international SST rivals provide a nearly complete permutation of the main cycle variants for this role. They comprise two afterburning turbo- jets, the twin-spool Bristol Siddeley Olympus 593 and the single-shaft General Electric GE4/J5; and two turbofans, the Kuznetsov NK-144 with conventional afterburner and the Pratt & Whitney JTF17 with duct burning. The choice by each company largely reflects its background of design experience to date, and in the face of such divergence of expert opinion it would be presumptive to make any forecast as to which con- figuration is likely to prove the winner. In the V/STOL field, Rolls-Royce has from the outset led the way technically and in the breadth of application of its lift jets. These range from the pioneering RB.108, now in inter- national use in hover rigs; through the RB.162, powering all Continental Europe's V/STOL projects; and so to the third- generation RB.189, which will be the basis of the new, as yet undesignated, R-R/AIlison Anglo-US advanced lift jet Backed as it is by a series of international development agreements, the lift jet (together with deflected- or vectored- thrust main engines) seems certain of becoming the prime mode of V/STOL propulsion. Bristol Siddley's highly original vectored-thrust plenum chamber turbofan concept suffered considerably under the British Government's programme of cancellations in 1965, and in reduced form would now appear to depend on the Hawker Siddeley P.I 127. The only other engine-company-inspired V/STOL system is General Electric's fan-in-wing work in conjunction with Ryan. While its effectively higher by-pass ratio offers some real advantages, the concept does not appear to have created much interest among airframe manufacturers. It would in any case seem limited in application to relatively small aircraft. The remaining rotor lift systems, namely, the tilt wing, or tilt pro- peller, make few calls on new engine technology. Higher rated compressors, giving higher pressure ratios in fewer stages, together with cooled turbines operating at higher gas entry temperatures, are making major contributions to the development of the high by-pass ratio turbofan for the next generation of transport aircraft. Pressure ratios as high as 25:1 and take-off temperatures in the region of 1,300°K have facilitated the design of engines such as the 8:1 BPR General Electric TF39, the 6:1 Rolls-Royce RB. 178-51 and the 5:1 Pratt & Whitney JT9D. These turbofans are among the most power- ful engines under development today and have ratings in the 40,0001b to 50,0001b bracket. Most important of all, they will operate at an s.f.c. nearly a quarter less than that of the turbo- fans now in airline service. Backing this broad sweep of progress with the major categories of engine is a continuing series of advances in com- ponent performance and efficiency, in materials and mechanical design and in applying the practical lessons acquired from the now vast funds of turbine operating experience built up by the prime manufacturers. As the leaders in this respect, Pratt & Whitney civil and military turbine engines have completed no less than 84 million hours in service. The time-between-over- hauls of these and Rolls-Royce civil engines are now in the 5,000hr to 6,000hr bracket with no signs of settling at this level. Exotic materials such as beryllium, which is the subject of a joint Anglo-US research programme, offer remarkable pros- pects for weight reduction. Beryllium, with its low weight and high strength properties, provides the opportunity of operating compressor blading at significantly higher tip speeds. This in turn raises individual stage pressure ratios to a point where only a third or so of the number of stages would be required by today's engines. Air transpiration cooling of turbine blades provides a further promising area for research which could facilitate valuable ipcreases in turbine entry temperature. These portents for the future are a far cry from the pioneer- ing achievements of Whittle's W.I engine of a quarter of a century ago. They are given size and magnitude in a recent statement by General Electric on its GE4/J5 engine for *s US supersonic transport programme—the peak overall effi" ciency of this 50,0001b-thrust afterburning turbojet will be 42 per cent, nearly double that of the best present-day engines. With advances such as this on the horizon, could it possibly K that the turbine's next quarter century will hold no surprises?
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