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Aviation History
1952
1952 - 1588.PDF
692 FLIGHT 80 90 _ 100 COMPRESSOR R.P.M(%of max.) (Above, left) Complete turbine stator assembly, including secondary "leak-control" shroud rings. (Right) Third and fourth stage rotors (for the air screw turbine) complete with output shaft. Note that the final-stage blades are not shrouded. Fig. 1 (extreme left) De signed performance curves of sea level static perform ance in I.C.A.N. con ditions. Fig. 2 (centre) Designed max. continuous power performance at altitude in I.C.A.N. conditions. ALTITUDE (ft X1.000) (Below) Schematic diagram of fuel system. INLET PROTEUS 705 . . . trailing edge of the inner drum a spinner-like tailcone of sheet stainless steel is internally flange-bolted. Having described the detail design of the engine, it remains now only to give some outline of the performance. The basic data are given in the accompanying curve, Fig. i, which relates to sea level static performance in I.C.A.N. conditions, whilst Fig. 2 defines the altitude performance at maximum continuous power rating, i.e., with compressor r.p.m. at 97.5 per cent of maximum, and power turbine r.p.m. at 9,500. It is of point to note that these data were calculated on the basis of a 17-in diameter jet nozzle, and for the altitude cases an air intake efficiency of 90 per cent was assumed. Emphasis must be given to the fact that these curves were evolved some little time ago, and relate to the designed per formance; they are thus definitions of expectations. During the first runs of the engine, however, the following figures were obtained, both on the dynamometer and with the airscrew, and using a 20-in nozzle :— Compressor r.p.m. 11,000 11,500 12,000 B.h.p. 2,630 3,350 4,100 Jet Thrust (lb) 620 770 920 Specific Consumption (Ib/e.h.p/hr) 0.62 0.58 0.55 Jet Pipe Temperature (deg C) 430 455 485 It is patent that, on this showing, the original expectations tended toward the conservative. Certainly, it may be observed that the nozzle area differs, and by ringing the changes with nozzles the performance can be radically altered—so much so as to render the worth of specific figures questionable. In this instance, how- BAROMETRC PRESSURE CONTROL —ll THROTTLE •""!<'" INPUT "SPSS DELIVERY S2E2 SERVO VALVE IDLING ADJUSTMENT ever, the matching of airscrew characteristics, engine performance and aircraft installation (i.e., in the Britannia) fixed the nozzle diameter at 17m, and the only reason a 2oin nozzle was used for the initial engine runs was that, at ground level, it produces turbine outlet swirl conditions closely comparable to those given by a 17m nozzle at 35,000ft—the mean cruising height of the Britannia. It has been made apparent in recent issues of Flight that, in the Britannia, the Bristol Aeroplane Company is producing an aircraft which will set new standards in commercial airline operating economy. It must be a source of considerable satisfaction to everyone at Filton that, if the initial runs are indicative of the future standard, the engines for this outstanding aircraft will, in fact, be even more efficient than was intended in their design. C.B.B-W.
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