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Aviation History
1965
1965 - 0030.PDF
I6OO I2OO 7OO aoo ISA-2O° ISA-IO°C ISA I.SA.*100C I&A.+2O°C BS Gnome H.I 200 one-hour power againsttemperature at sea level AERO ENGINES HELICOPTER POWERPLANTS: THE WORLD SCENE ... h.p. free-turbine JFTD-12 engine for the Sikorsky S-64 while the associated company in Canada produce a free-turbine PT6B engine of 550 h.p. for the experimental Hiller 1099 and the Kaman Huskie. In the United Kingdom there are two companies producing engines ranging from 650 h.p. to 2,500 h.p. Bristol Siddeley produce the free-turbine Nimbus engine flat-rated at 685 h.p. to 40°C ambient temperature and the free-turbine Gnome H.1000 and H.I200 of 1,050 h.p. and 1,250 h.p. respectively. The Coupled Gnome is a special variant complete with coupling gearbox giving 2,500 h.p. output. Bristol Siddeley hold licence rights with General Electric and also with Turbomeca for their turboshaft products. Rolls/Napier produce the free-turbine Gazelle engine of 1,650 h.p. for the Westland Wessex 1 and 3 and Belvedere. In France there is one company, Turbomeca, producing engines ranging from 400 h.p. to 1,500 h.p. The Astazou II is a fixed-shaft engine of 530 h.p. The Artouste HC and IIIB are also fixed-shaft engines of 400 h.p. and 550 h.p. respectively, both being flat-rated to about 40°C ambient temperature and used in the Sud-Aviation Alouette 2 and 3. The Bi-Bastan is a coupled engine of 1,800 h.p., similar in concept to the Coupled Gnome but using fixed-shaft engines. The Turmo III free-turbine range gives powers from 1,200 h.p. to 1,500 h.p., variants being fitted in the Super Frelon and the SA.33O. In Germany two companies are producing or developing engines ranging from 100 h.p. to 2,300 h.p. BMW produce the fixed- shaft 6012 of 100 h.p. for the Dornier Do32 and also the 6022 of 250 h.p. for the Bolkow 105. Daimler Benz are busy on the 1,000 h.p. free-turbine PTL.6 and the 2,300 h.p. PTL.10 Although information on Russia is somewhat speculative, two companies produce engines ranging from 700 h.p. to 5,000 h.p. A team led by Izotov produce turboshaft engines of 400 h.p., 700 h.p. and 1,300 h.p. while the Soloviev design team are responsible for TB-2B turbines ranging from 4,600 h.p. to 5,000 h.p. These engines are used in various Mil and Kamov helicopters of gross weights from 5,0001b to 85,0001b. It can be seen that the free-turbine engine emerges as the most effective type for general helicopter use. Compressor types vary, but the axial-cum-centrifugal is used most widely. Turbines are all axial. The fully annular combustion chamber is widely used. General Electric and Lycoming are the major US producers of helicopter turbines. In Europe, Turbomeca have consistently played a leading part, but recently Bristol Siddeley, by a judicious blend of licensing and native development, have emerged as a large producer. Typical Turboshafts Typical of present-day helicopter engines is the Bristol Siddeley Nimbus, developed under the original Turbomeca licence and used in the Westland Scout and Wasp. The power unit comprises a two- stage axial and single-stage centrifugal compressor running at 35,000 r.p.m., with an air mass flow of 11.lib/sec and pressure ratio of 6.4 : 1. The combustion chamber is fully annular with a central rotating fuel sprayer. The gas generator turbine is two-stage axial and the free output turbine a single axial stage running at 28 700 r.p.m. The engine incorporates a reduction gearbox with an output speed of 2,150 r.p.m. Flat-rated one-hour power is offered at 685 h.p. to tropical conditions. The Bristol Siddeley Gnome is used in medium helicopters such as the Westland Whirlwind and Wessex 2 and 5, the Agusta Bell 20 FLIGHT (mernot/omi 7 January I96S 3OO 2OO I.SA ISA^B°C I£A>3O°C BS Nimbus one hour power against ambient temperature GE 764 s.h.p. against forward speed (in knots) at sea level and i.s.a. 3OOO I5OO MAXMUM — W — ILITARY _ NORMAL __ .—•—" .— " P;55 L^/SH . -^ 50 IOO I5O FORWARD SPEED —KNOTS 2OO 25O 204B and the Boeing Vertol 107. The engine uses a ten-stage axial compressor running at 26,300 r.p.m. with an air mass flow of 12.81b/sec and a pressure ratio of 8.25 :1. The combustion chamber is a fully annular type with 16 downstream simple sprayers. The gas generator turbine is a two-stage axial type and is followed by a single free axial power turbine running at 19,500 r.p.m. The engine is offered in two versions giving as one-hour powers either 1,050 h.p. or 1,250 h.p. The General Electric T64, licensed by Bristol Siddeley, is used in the heavy Sikorsky CH-53A and the Hughes XV9A research helicopter. The engine incorporates a 14-stage axial compressor running at 17,000 r.p.m. with an air mass flow of 24.51b/ sec and a pressure ratio of 12.6 :1. The combustion chamber is a fully annular type with 12 downstream duplex sprayers. The gas generator turbine is a two-stage axial type followed by a two-stage free output turbine running at 13,600 r.p.m. This engine gives 2,850 h.p., can be supplied as a turboshaft, turboprop or gas generator and is designed to incorporate suitable reduction gear- boxes giving output speeds appropriate to each application. Various kinds of helicopters have specific engine installation requirements. In the light/medium helicopter, reliability is at a premium because it will often operate in all weather conditions away from fixed bases. Engine maintenance must be straightfor- ward and easy. Preventive inspection could well take the place of long overhaul life, because long life implies part replacement, which could be difficult in the field. Light weight is essential and a typical 250 h.p. turbine complete with gearbox can weigh as little as one-quarter of the equivalent piston engine. The helicopter itself can therefore be smaller and lighter. Turbine engines have to meet "hot and high" requirements and, because the decay of power with ambient temperature is greater for turbines than for piston engines, more power has to be installed. But this factor is overborne by the lower engine net dry weight. Although s.f.c. is important, mission length is generally such that the advantage remains with the turbine despite operation at around 50 psr cent design power. In the smaller gas turbines there has been great debate on the merits of fixed and of free power turbines. The French have operated hundreds of Alouette 2 and 3 helicopters successfully with the fixed-shaft Artouste and Astazou. Their great virtue lies in the rapid response so essential for manoeuvring. The fixed-shaft engines run more or less at constant speed, and power is varied by change of gas temperature alone. The acceleration delay in increasing turbine spsed is thereby overcome and the power response is almost instantaneous. A clutch is necessary for starting. Continued on page 21
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