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Aviation History
1954
1954 - 0970.PDF
438 FLIGHT The old and the new: the single Pratt and Whitney J57 turbojet in the foreground develops roughly the same power as can all the seven R2800 Double Wasps lined up in the rear. The Quest for Power... other fields in which the airframe company is also concerned, including fuel, oil, electrical and ignition systems and, if such equipment is fitted, an automatic engine-control system. The last-named can be electro-hydraulic, or of an electronic nature, die latter probably using magnetic amplifiers. These control systems are particularly necessary where an afterburner is fitted, so that fuel flow, r.p.m., jet-pipe temperature, and nozzle area can all be inter-linked automatically. Afterburners themselves—or reheat jet-pipes, as they are sometimes known in this country—are generally accepted for increasing the performance of high-speed fighters. Basically, these devices are just enlarged tailpipes attached to the rear of the engine, within which additional fuel can be injected and burnt. The basic configuration may take several forms, according to the degree of augmentation sought. Generally, a diffuser section is attached directly behind the engine tail-cone, with fuel injection nozzles and flameholders at the point of maximum diameter; some of the theory involved is briefly discussed in the section on ramjets, which follows later. Since the mass-flow, temperature and gas pressure may all be increased by reheat, it is essential to have a larger propelling nozzle than is needed by the basic engine. If the nozzle were kept the same size, the internal gas pressure would rise dangerously and, as the flow through the turbines is subsonic, would be transmitted forward to ruin the performance of the engine. On the other hand, an afterburner is essentially a boosting system for intermittent use, and considerable thrust-loss would result if an enlarged nozzle were permanently fitted. Accordingly, the nozzle area has to be made variable, most current systems employing a pair of "eyelid" shutters moved by a mechanical actuator. Owing to the tremendous flow of very hot gas through the afterburner, it is very difficult to carry out full-scale testing of a new design, and the initial development will be done with models; it is common practice to use a model of about one-third scale, Lay cock Engineering, Ltd., Victoria Works, Millhouses, Sheffield 8, make "Layrub" vibration-resistant trans missions which run without lubrica tion or metal-to-metal contact. A typical example is the drive between the Britannia accessory gearbox and the driving Proteus turboprop. The company also state that the produc tion Seamew will be powered by a Mamba 6, from which a Layrub coupling will drive accessories. Leytonstone Jig and Tool Co., Ltd., Liverpool Works, High Road, Lon don, E.10, are major suppliers of jigs for engine production; their jig castings are widely used in the manu facture of nearly all British power units. Lodge Plugs, Ltd., Rugby, have served the British Aero engine in dustry for 50 years. Their present products include gas-turbine igniter plugs and piston-engine sparking plugs—all with Sintox insulators— and screening and testing equipment. Lodge LR102/1 igniter plugs are found on the Avon RA.7, and a pair of Type 433 flame igniters is used to light up the Olympus. Low Moor Alloy Steelworks, Ltd., Low Moor, Bradford, Yorks, make all kinds of gas-turbine steel and, in conjunction with their associated company, Low Moor Fine Steels, fabricate these alloys by a number of processes. Of exceptional im portance is the French Ugine-Sejour- net process for extruding stainless steel, using glass as a lubricant; the company hold the English rights. By this means, gas-turbine rings and flanges can be made from wrapped-around extrusions, which is proving more satisfactory than cutting off lengths of centrifugal casting. Joseph Lucas (Gas Turbine Equip ment), Ltd., Birmingham and Burn ley, are responsible for the design and production of the complete fuel system, burners and combustion chamber of the majority of British gas turbine aero engines. Then-fuel pumps, which operate at up to 4,000 r.p.m. yet are lubricated only by the fuel, can deliver various flows at pressures of 2,000 p.s.i. For this work finish tolerances of the order of 2 micro-inches are required. Various fuel systems are in produc tion for low, medium and high-alti tude flight. An advanced type of pump is that which, driven by a tiny turbine running at 24,000 r.p.m. on compressor bleed air, supplies fuel to a turbojet afterburner with a com bined flow-rate and pressure of 2,000 gal/hr at over 600 p.s.i. Progenitor of a large family is a combined fuel control unit for expendable turbo- jets which, in a simple and compact form, embodies an altitude control, proportional-flow throttle valve, spill valve and shut-off cock. A particu larly neat device is a gas-temperature control unit, the sensing head of which (mounted downstream of the turbines) has quartz and steel rods end-to-end so that differential expan sion actuates a bleed valve which, in turn, reduces the fuel flow to restore the optimum gas temperature. Magnesium Elektron, Ltd., Clifton Junction, Manchester, make a great contribution with "Elektron" mag nesium-zirconium alloys, which en joy a unique combination of low specific gravity, pressure-tightness and high creep-resistance. In countries producing British en gines under licence many foundries are turning out Elektron alloys with the permission and assistance of the Manchester company. Magnesium- zirconium-zinc-thorium alloys ZT1 and TZ6 are now in wide use, par ticularly in the manufacture of the very latest high-pressure turbojets. Manchester Oil Refinery, Ltd., Traf ford Park, Manchester 17, market "Lumor" and "Glomor" for the fluorescent detection of cracks. The suspected part is painted with the appropriate ink and, after allowing about one minute's drying, is examined in ultra-violet light. Sur face cracks are revealed by brilliant green fluorescence. Manganese Bronze and Brass Co., Ltd., Elton Park Works, Hadleigh Road, Ipswich, manufacture "Oilite"
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