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Aviation History
1956
1956 - 0575.PDF
11 May 1956 575 data. Its design is the result of a careful study into the power require-ments of future helicopters. Pressure ratio, top temperature and mass flow are the optimum to satisfy these requirements; the engine can beinstalled at any angle to suit the application; and the exhaust system minimizes the gas exit-velocity to provide for the maximum shaft-power. The slimness and light weight of the Gazelle simplify its installation in an airframe, and in a twin-engined helicopter allow fora passageway around the forward engine. A new departure is the employment of a common fabricated casingfor the six flame tubes. Single-lever control is provided, with auto- matic compensation for variation in ambient temperature and pressure,turbine-inlet temperature and maximum and minimum torque-limita- tion. In the event of failure of one engine in a twin-engined aircraftthe power of the remaining unit is automatically doubled or increased to the emergency rating, and a fundamental advantage of the free-turbine layout is that the rotor-speed and engine-speed can each be adjusted to the optimum value under all flight conditions. Accessoriesare mounted on the upper surface of the intake casting. Recent types of Gazelle discharge exhaust gas through four circular pipes. Prototype units have passed their 25-hr flight-approval test. Theengine has considerable development potential. The design rating was exceeded on the initial calibration run, the s.f.c. is below the estimatedfigure and production Gazelles should be suitable for all helicopter 1 Napier Oryx (NOr.5 rating). Single-shaft turbo gas-generator. Twelve-stage compressor, five combustion chambers and two-stage turbine; four-stage auxiliary compressor. Diameter, 19£in; length, 83|in; dry weight, 500 Ib; mass flow, 15.3 Ib/sec; pressure ratio, 6.15:1 (overall pressure ratio of gas from delivery valve, 1.7:1); maximum output, 950 gas h.p. at 22,600 r.p.m. with s.f.c. of 0.62. Napier N.R.E.17. Rocket motor. The drawing shows the chamber and valve group for the N.R.E.17, which has a thrust of about one ton and presumably has missile applications. The propellants are high-test peroxide and kerosine. applications between 1,250 and 1,800 s.h.p. The engine was designedfor the twin-rotor Bristol 192 and will also be used in the Westland Wessex—and, probably, in certain fixed-wing aircraft. It is regardedas likely to be one of the company's principal products for several years to come. Oryx. With this unique unit Napier set out to produce a light andefficient engine capable of putting out all its power in the form of a flow of gas at a temperature and pressure suitable for helicopter tip-jetpropulsion, without tip-burning (a singularly quiet system specified for the Hunting Percival helicopters). The resulting Oryx is an exceed-ingly slim engine. The surplus turbine power is expended in driving a permanently coupled auxiliary compressor which delivers fresh airto an uptake volute where it is mixed with all the efflux from the main power section (in contrast to the Rotodyne Eland) to give a final outputat 678 deg K. and 23.5 lb/sq in abs. During the starting cycle the large non-throttling valve is opened todischarge all the gas directly to atmosphere. The valve is then partially restricted to simulate the back-pressure of the helicopter rotor, afterwhich the gas can be passed to the rotor itself with the engine running normally. The full range of accessories can be driven off the wheelcaseat the front end. Several prototypes have run, both on the bench and in the P.74 helicopter, and a full type-test was completed earlythis year at 780 gas h.p., this being the first such type-test to be passed by a British helicopter gas turbine. Later Oryx are more powerful, thetype-tested rating having been raised first to 825 and then to 950 gas h.p., and the NOr. 10 being rated at 1,250 gas h.p. Ramjets. Last autumn visitors to the National Gas Turbine Estab-lishment were allowed to see a test vehicle designated RJTV 27 which had been designed and manufactured for the Ministry of Supply by theNapier Flight Development Establishment at Luton. The ramjet fonned a fuselage roughly 16ft long, with a diameter of about 20in over thecylindrical combustion section. Launching was effected by rocket boost from an inclined ramp, as shown in the photograph opposite. Napier developed the fuel system to operate on gas pressure, or, alter-natively, on the power of a ram-air turbo-pump. Very extensive development has been conducted by the company into all aspects ofthe operation of such vehicles. The RJTV 27 had a simple pitot intake, from which one mayconclude that the design Mach number is not very great (although it is Napier Gazelle NG.1. Free-turbint helicopter engine. Multi-stage compressor, cannular combustion chamber with six flame tubes and independent compressor- and power-turbines. Overall height, about 70in; maximum diameter at intake, 33£in; dry weight, restricted; mass flow and pressure ratio, restricted; maximum rating (5-min), 1,260 s.h.p. (net residual thrust, 260 Ib) at 20,400 compressor r.p.m. and output-shaft speed of 3,000 r.p.m.; one-hour rating, 1,100 s.h.p. at 19,800 r.p.m. (output, 3,000 r.p.m.); continuous, 920 s.h.p. at 19,000 r.p.m. (output, 3,300 r.p.m.). Other ratings are NG.2 (1.650 s.h.p.). NG.3 (1,800) and NG.4 (2,000). clearly at least 1.5). Nevertheless, in March this year the companyannounced that such a vehicle had "reached a height greater than any previously attained in the United Kingdom by a ramjet-poweredvehicle," in spite of the fact that the flight had to be curtailed when still under full power in order to prevent possible danger to shipping.Rocket Motors. The first tangible evidence of Napier's work in this field was made public at the 1955 S.B.A.C. Exhibition, when two displaycombustion chambers were shown. One of these was a development chamber which, at a guess, was rated at 2,000 to 2,500 lb thrust. Thechamber was regeneratively cooled, the fuel feed entering at the throat, and the whole assembly was machined from steel forgings. The otherunit was presumably a production motor, with the designation N.R.E.17. Of similar size to its companion the N.R.E.17 was a sheet-steel assembly,running on high-test peroxide and kerosine. ROLLS-ROYCE. Rolls-Royce, Ltd., Nightingale Road, Derby. Asalways, this renowned company is bearing a tremendous responsibility for the propulsion of all types of military and civil aircraft. Over 90 Rolls-Royce: Conway RCo.5 unit on bench-test.
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