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Aviation History
1953
1953 - 1020.PDF
174 FLIGHT THE VIPER . . . Balancing.—The compressor rotor is first balanced on its own, plasticine being added to suitable portions of the drum until correct balance has been achieved. Metal is then removed from ribbing strips on the front and rear steel discs according to the weight of plasticine added. The rotating assembly is* then completed right back to the turbine and balanced, as many as four turbine blades being cropped up to ^in. if necessary. Tailpipe.—The jet cone is yet another Sankey product in Nimonic 75 sheet. It is a precision spot-welded assembly with a smooth central cone located by three streamlined struts. In the Jindivik, the tailpipe is cooled by an induced airflow. Fuel System.—The accompanying drawing of the fuel pump, and the diagram of the system itself, do not require any great explanation. The choice of a gear-type fuel pump is almost unique, and has only been made possible because of the small fuel flow and unusually low pressure differential. It has worked excellently with all types of fuel, and is also exceptionally cheap to produce. Delivery from the pump is made at about 450 lb/ sq in. From the spill valve, the fuel passes to a pressure-increas ing valve which is solely to provide a useful positive pressure when the engine is being started. The fuel then passes through the linear throttle valve, which is positioned by an irreversible electric actuator. This actuator, incidentally, was originally de signed for the Jindivik pilotless target, and its function is to translate a radio signal from a ground, or airborne, control unit into mechanical movement of the throttle. No doubt it would not be necessary in a piloted aircraft. From the throttle, the fuel flows through the governor control valve which moves in sympathy with the servo pressure, which in turn is a function of the position of the mechanical governor. Next in line comes the emergency shut-off valve, which provides virtually instan taneous interruption to the flow of fuel. It is simply a spring- loaded valve held back by a solenoid. The fuel then passes to the burner rings. Other items in the system are the governor and the B.P.C. unit. The governor is, unusually, of a purely mechanical type, and this not only offers some advantages in reliability and cheap ness of manufacture, but it also operates accurately irrespective of the density of the fuel. It is mounted on a common shaft with the fuel pump. The barometric pressure control unit by-passes a proportion of the pump delivery according to the throttle position and compressor intake pressure. It contains a sylphon tube housed in a chamber which communicates with the com pressor intake, and is therefore maintained at Pi, or compressor ram pressure. At present, the entire fuel system is composed of rigid pipe, with the exception of a Powerfiex final hose to the main burner rings, and later Vipers may dispense with the rigid pipe com pletely. Lucas is the company principally concerned with the fuel system, and the throttle actuator is a product of Rotax Australia. Surprisingly, there is a tendency to switch over to kerosine; most of the Viper time has been logged on wide-cut gasoline. Oil System.—The oil pump is of the two-piston, double-acting type, with four deliveries. From the pump, the oil is fed to an external transfer block and then, running in rigid steel pipe held in welded clips, it is passed to the centre and rear main bearings. The pipe leading to the rear bearing runs down the inside of the annular combustion chamber, but is screened by the rear-bearing support cone and tertiary air from the combustion itself. The front bearing is fed through drilled passages in the air-intake casting. As previously mentioned, each bearing is supplied with £ pint of oil/hour through a separate feed. At present, there is no oil recovery and all the hot, used oil is dumped overboard. Oil from the front bearing is drained through the "seven o'clock" strut in the compressor intake, and the flow from bearings 2 and 3 is passed out as mist and finally vapour through the jet pipe. Another half-pint/hour is fed to the front accessories and drives, and is also drained overboard: total delivery is therefore 2 pints/hour. Some earlier engines had provision for a saddle oil tank around the front of the compressor, but the tank is elsewhere in the Jindivik. Various types of lubricant have been used with the Viper, but by far the best performance has been obtained with the synthetic Esso Turbo-oil 35, and this is considered standard. Starter.—The original idea was that the Australians would make a portable starter unit which would be manually held up against the fuselage of the Jindivik, to engage mechanically with the drive shaft in the "three o'clock" intake web. It was soon apparent that this method was fraught with difficulties, chiefly owing to the impossibility of getting accurate alignment. Armstrong Siddeleys suggested a direct air system in which a compressed air jet is directed against the turbine blades. This has now been adopted, and is shown in an accompanying drawing. Air is taken from external bottles—or a test-bed air line—at 120 lb/sq in., and passed to a pair of ^in pipes on the turbine mani fold, blowing tangentially at 30 deg to the tips of the turbine blades. The Viper is not at present a fighter engine and has not had to meet the "10 seconds" starting time requirement. Never theless, the Viper accelerates very well from rest to about 2,000 r.p.m. at which point the engine pulls away. Idling speed of 5,500 r.p.m. is reached in about 35 seconds. The starting air line has a remote valve control and the engine has merely a non-return valve to stop air blowing out when the line is broken. Accessories.—The Jindivik is, as might be expected of a pilotless aircraft, all-electric. Consequently, present Vipers carry no accessories apart from a generator, and this, being a product of Rotax, Australia, is bolted on in that continent. It has a capacity of H kW, and is blast-cooled by ram air. Interest attaches to its drive, which consists of an internal gear driven from the front of the compressor, and situated just forward of the front bearing. The Present Position.—In order to complete preliminary testing quickly, Armstrong Siddeleys first built six development engines. A number of production engines have now been made of the ASV.3 type, cleared for 25 hours flight. In the meantime, the Jindivik 1 is completing its trials with the Adder, and the Viper-powered Jindivik 2 should fly in the autumn. The Vipers so far built have been painted with inhibit ing fluid and sealed in tin-lined boxes containing silica gel desiccant, and then crated and shipped to the D.A.P. in Mel bourne. Here, they have been fitted with the appropriate Australian-built components, and mounted in Jindivik airframes. The Australians have quite a stockpile of Vipers now, and it is hoped to get four to five flights per aircraft without any overhaul being necessary. In fact, it appears now that the short-life character of the Viper is greater than that of the airframe, for the Jindivik is likely to be written off before the engine life expires. The ASV.5, on the other hand, is being developed as a perfectly normal engine for piloted aircraft, and should have a life fully equalling that of any other turbojet. It resembles the ASV.3 but is generally strengthened; the combustion chamber, for example, has flame tubes with a corrugated periphery, each corrugation being spot-welded to the adjacent flame tube section. Heavier gauges of sheet are being used over most of the engine, and a number of other detail alterations incorporated. These changes are likely to increase the weight of the long-life Viper to some 450 lb, but this is counter-balanced by a probable future increase in thrust. At present, Armstrong Siddeleys are building an ASV.5 pro totype and are developing the engine for use in the Percival P.84 jet Provost; for this application, at least, the Viper should have plenty of thrust in hand. Finally, it is worth noting that the French private aircraft firm of Marcel Dassault have become very interested in the long-life ASV.5 and a licence has been agreed by which they will build and develop this Viper for their own airframes. They now have two short-life ASV.3s in order to gain some experience of this neatest of all power plants. The Vipers so far cleared for publication are: the ASV.l (1,145 lb thrust), ASV.2 (1,575 lb), ASV.3 (1,640 lb), ASV.4 (1,750 lb), ASV.5 (1,640 lb), and the ASV.6 (1,900 lb). Following is a list, provided by the engine manufacturers, of the principal suppliers of material and components. W. T. G. SUPPLIERS OF MATERIALS AND COMPONENTS Forgings.—Geo. Turton Platts and Co., Ltd. (compressor rear shaft); Tubes, Ltd. (turbine mainshaft); Firth Vickers Stainless Steels, Ltd. (turbine stator shroud). Castings.—High Duty Alloys, Ltd. (air-intake body, compressor casing, front diaphragm, front bearing housing, gearbox body and cover, and other parts); Fozel Castings Co., Ltd. (oil-connection body); J. H. Lavender and Co., Ltd. (drain-valve bodies). Stampings.—South Wales Forgemasters, Ltd. (turbine disc); High Duty Alloys Ltd. (compressor rotor discs); Daniel Doncaster and Sons, Ltd. (internal gears); Faulkners, Ltd. (seal ring housing); Dudley Drop Forgings, Ltd. (locknut); Brett's Stamping Co., Ltd. (oil seal housing). Blading.—High Duty Alloys, Ltd. (compressor rotor blades); Firth Vickers Stainless Steels, Ltd. (turbine blade material); Brunton's (Musselburgh), Ltd. (formed strip for compressor stator blades and turbine inlet guide vanes). Bought-out items.—Hoffman Manufacturing Co., Ltd. (bearings); The Palmer Tyre, Ltd. (flexible pipe), Pilgrims Way Motor Co., Ltd. (4-delivery metering oil pump); Lucas-Rotax (Australia) Pty., Ltd. (generator and electric actuator for Jindivik engines); Coopers Mechanical Joints Ltd.; Alfred Roberts and Sons, Ltd.; Super Oil seals and Gaskets, Ltd.; Stillwell and Sons Ltd.; James Walker and Co., Ltd.; British Piston Ring Co., Ltd.; Automotive Engineering Co., Ltd.; Precision Rubbers, Ltd.; Benton and Stone, Ltd.; A. Poole and Son; Mole and Son; Simmonds Aerocessories, Ltd.; and Fletcher Bros. (Pressings) Ltd. (breathers, grommets, oil seals, nameplates, washers, piston rings, circlips, bushes, tubing, sleeves, nuts, shims, tabwashers, and retaining tabs, etc.). Sub-contract items.—Joseph Lucas, Ltd. (fuel system and controls); Joseph Sankey and Sons, Ltd. (stator-blade rings, combustion chamber, flame-tubes and jet-pipe); Metropolitan Vickers Electrical Co., Ltd. (machining of turbine blades), Tungum Co., Ltd. (rigid fuel-pipe units).
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