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Aviation History
1960
1960 - 0587.PDF
I. JGHT, 29 April 1960 587 GNOME Design Features of the D.H. 1,000 h.p. Turboshaft Engine 1AST week de Havilland Engines announced that the Ministryof Aviation have ordered a large quantity of 1,000 s.h.p.J Gnome turboshaft engines for RAF Whirlwinds. This is the first bulk order for the Gnome, and manufacture of produc-tion engines to the agreed standard is already in hand at Leaves- den. The engines will be installed in existing RAF Whirlwindsand in new Mk 10 aircraft. Other applications of the turboshaft Gnome include the Westland Wasp and Westland Wessex 2, anexport order has been signed for the three-engined Agusta 101G and other applications are being discussed. There is also a turbo-prop version, currently under development for several aircraft. The engine ordered for the RAF Whirlwinds is the H.1000of DGe.2 rating. Essentially this has a gas-generator similar to that of the DGe.l, but the new mark can be at once distinguishedby its cleaner appearance (above). The D.H. Propellers com- puter, which previously formed a "horse-collar" around the in-take, is now airframe-rnounted; and the throttle actuator is posi- tioned on the port side. At the 6-o'clock position below theintake has been added a novel centrifugal fuel filter, discussed later in this account. At present this filter is of American origin,but all other portions of the engine, right down to raw materials, are British. Later Gnomes will be more powerful. The twin-enginedWessex 2 will have the H.1200, with a normal take-off rating (standard day, sea level) of 1,250 s.h.p., and a 2|min contingencyrating of 1,350 s.h.p. Since the Wessex transmission has a limitation of 1,500 h.p., the surplus 1,200 h.p. should conferoutstanding performance reserve for single-engined flight and operations in tropical or high-altitude conditions. The two engineswill be installed side-by-side at 35°—previously the Gnome was not cleared to operate far from the horizontal—and drive intoa common secondary gearbox of D.H. Engines design. Incor- porated in this box are simple helical reduction gears, and a pairof over-running freewheels, to allow single-engined flight or ground running. The complete installation should be type-testedand in production next year. Following it in development is the H.I400, of greater power. As far as possible D.H. Engines have kept the basic powersection of the Gnome identical to that of the General Electric T58. This American engine was fully described in our issue ofJanuary 17, 1958, and a full description with cutaway drawing of These diagrams show the schematic layout of the electrical system (A), fuel system (B) and mechanical linkage (C), all of which differ considerably from their counterparts in the American 758 A 1, Torque limiting switch; 2, torquemeter transducers; 3, intake air-temperature thermistor; 4, power-turbine tachometer (control); 5, power-turbine tachometer (indicator); 6, reduction gearbox oil pressure (transducer); 7, accessory drive casing oil pressure (transducer); 8, anti-icing valve; 9, gas-generator dual tacho- meter; 10, connection to cockpit; 11, inter-turbine thermocouples; 12, throttle actuator; 13, computer; 14, aircraft 28V supply. the original Gnome appeared in our August 15, 1958, issue. It isnow appropriate to outline some of the entirely British accessory and control systems which have been developed for the productionGnome and which had not been finalized when our earlier descriptions were prepared.The fuel supply and engine control systems are entirely British (diagrams below). They comprise an electric computer by deHavilland Propellers, operating in conjunction with a Lucas fuel controller. The pilot selects the desired helicopter rotor speed bymeans of the speed-select lever in the cockpit which is mechanic- ally linked to the computer. In addition to this speed-demandsignal, the computer is also fed with information on the per- formance of the engine (see diagram). The computer is thus ableto determine the changes in fuel flow to the gas generator required to ensure that the power turbine maintains a constant speed undervarying rotor load. It effects these changes by feeding a signal to an actuator mechanically linked to the fuel controller. Thecomputer performs this duty rapidly while at the same time preventing compressor surge, flame extinction or overheating ofthe turbine—this it does by employing its knowledge of com- pressor intake temperature and r.p.m. and the inter-turbinetemperature at any moment during the change. The fuel controller produced by Joseph Lucas (Gas TurbineEquipment) Limited, comprise a variable-stroke piston pump, a flow control unit, throttle and shut-off cock. The pump shaft isextended to drive a centrifugal function-generator where a fuel pressure is generated proportional to the speed but independent B 1. Fuel inlet; 2, centrifugal filter; 3, inlet guide vane actuator; 4, ambient temperature; 5, fuel pump; 6, pump stroke control; 7, ambient pressure; 8, fuel- flow control; 9. gas-generator top-speed governor; 10, pressure speed generator; 11, throttle; 12, shut-off cock; 13, oil cooler; 14, flow divider; 15, burner manifolds. C 1, Emergency manual throttle twist-grip on collective-pitch lever; 2, change- over toggle; 3, throttle actuator; 4, speed selector lever; 5, computer; 6, fuel pump; 7, pump stroke control; 8, fuel-flow control; 9, gas-generator top-speed governor: 10, pressure speed generator; 11, throttle; 12, shut-off lever; 13, shut- off cock; 14, power-turbine overspeed trip. \J! m Autofr.Monual
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