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Aviation History
1954
1954 - 0968.PDF
436 FLIGHT The Quest for Power... lb/sq in. This immense magazine holds no less than 130 tons of air at one filling, and the forces on its walls pose an interesting calculation. Valves release the air into any of a variety of test cells, the capacity of the magazine being so great that tests are rarely cut short by the supply pressure falling off. Firms without such facilities can do no more than press on with ground testing until a flight clearance test has been successfully completed. Then, as rapidly as possible, the engine will be got into the air. A suitable test bed is a valuable asset; not only does the aircraft have to be big to hold all the equipment required, but it should be multi-engined so that it does not have to rely on an unproven power unit. A good ceiling is another requirement, and it is not inappropriate at this point to record how valuable is the Canberra for such work. It may be noted in passing that it is American practice to mount the test engine without ducting on a pivoted cradle attached to the belly of a large aircraft so that it may be swung out of the bomb-bay during test runs. This type of installation is illustrated. Once in the air progress is accelerated rapidly. Not only is it possible to examine the performance of the engine at all speeds and altitudes and under all conditions of ram pressure and g loading, but it is possible to determine the handling of the engine from the pilot's point of view, so that provisional pilot's notes can be prepared. Even in flight testing, the engine requires a prodigious amount of instrumentation. Not only will automatic observers be fitted to record all instrument readings photo graphically, but some results, such as those of strain-gauges, can be telemetered to the ground and there analysed or put on a tape recorder. Flight testing is also die only means of proving fully the fuel and oil systems. Only in flight is it possible to assess their behaviour at high altitude, or under high acceleration loadings, and during dives and climbs and other critical periods. As for the engine itself, compressor stall or blade shedding may demand a hasty return to base, but huge test programmes can usually be completed in a few weeks of flying. Ground testing then changes in character from an analysis of performance to sheer make-and-break endurance testing. This is generally resolved into a series of cycles, each of which includes a prescribed number of hours at selected ratings from idling to full thrust. These cycles are made more and more arduous until the company feel able to tackle the 150-hour M.o.S. acceptance test, which itself consists of such a series of cycles. The engine submitted for this test is carefully inspected by the M.o.S. preparatory to its test, and is then sealed in its cell to run without attention. Such tests are extremely expensive; the 150-hour run for a 30,0001b-thrust engine will involve the consumption of at least 350,000 gallons of fuel. The feelings of a company confronted with failure after 149 hours can possibly be appreciated. The engine is now no longer experimental. Pilot production engines will be flowing through the shops and the manufacturer will probably be running from four to a dozen development engines at once, all of them different. This number will tend to increase for several years following. Towards the end of endurance testing, if not before, the decision will have been One of the first afterburners to see service; a reheat Allison J35 being installed in a U.S.A.F. Northrup Scorpion fighter. laboratory contains such mighty facilities as a test chamber capable of taking a 20ft-diameter airscrew and running it at a simulated alti tude of 100,000ft, and a test cell suit able for running 25,000 lb-thrust turbojets in the development of their fuel systems. Hardy Spicer, Ltd., Witton, Birming ham 6, are renowned in many fields; in that of aero engines they make helicopter transmissions and the uni versal joints and drives connecting aero engines and remote accessory- drive boxes. It is, for example, a Hardy Spicer drive which couples the Comet 2's accessory boxes to the Avon 503s. Heenan and Froude, Ltd., Worces ter, is a very familiar name in con nection with aero-engine test plant. They make all kinds of dynamo meters, working on eddy-current, hydraulic or electric principles, as well as complete stationary or tilt ing wings for installed engine tests, torque and thrust measuring gear, hangar and wind-tunnel test stands, and other equipment. It is safe to assume that the Gyron, Conway, and all our other big engines, arc being put through their full-scale tests with Heenan and Froude apparatus. Heli-Coil Corporation, 248 Shelter Rock Lane, Danbury, Connecticut, have built up a large business out of small coil inserts made of stainless- steel, diamond-section wire, for acting as a bearing surface for bolts in threaded holes in softer metals. Using 18-8 stainless steel, with u.t.s. of 180,000 p.s.i., thousands go into American turbojets every week: the J40-WE-22 saves £6 per engine on compressor stator blade bushings alone; the forward frame of the J47 has 50 Heli-Coils whereas the later J73 has 306; and Allison have gone from 61 Heli-Coils in the J35-A-27 to 193 in later versions. High Duty Alloy*, Ltd., Slough, Bucks, not only make a vast quantity of airframe forgings—some with a 12,000-ton press—but they are one of the biggest suppliers of gas-tur bine blading to a total of ten mil lion blades in Hiduminium alone. They also make basic structural parts of several of our important engines; although one of the company's Hiduminium alloys is more usual, many such components are made in magnesium-base alloy. An example is the main air duct and inlet casing for the Double Mamba, which is a sand casting in Magnuminium 220. High-Pressure Components, Ltd., 139 Kensington High Street, Lon don, W.8, make "Gyp" couplings and connections used on the Proteus turboprop and many other engines. Hughes-Johnson Stampings, Ltd., Langley Green, Birmingham, special ize in the more difficult forms of drop-forging, in all standard gas- turbine alloys, including titanium alloys. I.V. Pressure Controllers, Ltd., Forge Works, 844 Bath Road, Cran- ford, Middx, make such things as full-bore line solenoids for gas or liquid services at pressures up to 4,000 p.s.i. These are available for B.S.P. from iin to 3in, 24 volts D.C. Other valves handle corrosive acids. Imperial Chemical Industries, Ltd., London, S.W.I, are big enough to need a page to themselves; but in connection with engine manufacture it is appropriate to note the comple tion of development of their sodium hydride process, believed to be the only effective means of de scaling titanium metal and the Nimonic alloys. Industrial Engineering Co., Island Road and Suffolk Street, Philadel phia 42, Pennsylvania, have a com pact Hydra-Brake which, mounted like an accessory on an engine-drive pad, can be used to provide an accur ate measure of the power being de livered at the shaft. It is a form of water dynamometer, and the power is obtained by measuring the rise in temperature. A 1,000-h.p. unit i» 14in by lOin, and weighs 35 to 55 lb.
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