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Aviation History
1953
1953 - 0606.PDF
6oo FLIGHT AVON TESTING New Heenan and Froude Test-Beds at Coventry IN company with certain other firms, the Standard Motor Company, Ltd., are co-operating with Rolls-Royce in the manufacture of the Avon engine as part of the national engine supply programme. At the Standard works at Coventry, two comprehensive test-beds for these engines have been installed by Heenan and Froude Ltd. and were recently visited by Flight. These test-beds are similar to others being built by Heenan and Froude for D. Napier and Son, and for an extension factory of Rolls-Royce, both also engaged in Avon production, and the whole contract represents die first quantity production of large-scale test equipment for a turbine engine production programme. The thrust-cradles of the Coventry installation are stated to be equally suitable for the Bristol Olympus, de Havilland Ghost and Goblin, and Armstrong Siddeley Sapphire engines, as well as for more powerful units of the future. The layout of the Standard installation was influenced con siderably by the need to use existing buildings. These premises had been erected during the last war to house Heenan hangar stands for testing the Bristol Hercules engines which the Standard company produced under the "shadow-factory" scheme. In these plants the engines were mounted on nacelles some icft above floor level (as the engine power was absorbed by large-diameter airscrews), and the control room was elevated accordingly. The same position of control rooms was retained for the new turbine engine installation. As this form of construction provides a clear space below the control room floor, the opportunity was taken to instal there a battery room and to house the CO2 fire-extinguisher bottles and other equipment. The building is in the form of a capital letter H, housing two plants and having a common double control room. The space at one end is roofed over to form a rigging shop where engines are prepared for erection on the cradle, and care has been taken to reduce the change-over period between engine installations to as short a time as possible. An Avon mounted in one of the test-beds. To the beams at the intake end a known thrust can be applied by means of weights, to check the accuracy of the thrust readings. The control room is on the left. The basic essentials of the plant are: (a) a thrust cradle, on which the engine is bolted and arranged so that the thrust is transmitted to accurate measuring gear, remotely situated in a control room; (b) means of storing, supplying and measuring the fuel consumed by the engine; (c) a control panel, placed behind an observation window in the control room, with measuring instruments and controls; (d) ventilating and heating plant, fire- fighting equipment, engine accessory loading equipment, and other auxiliary plant; (e) sound-proofing. These items are described in more detail below. The engine thrust cradle is large enough to take bigger engines than the Avon, and is capable of dealing with greater thrust than is actually developed by that unit. (Maximum stated thrust for the Avon is 7,500 lb without re-heat.) The engine is fixed by brackets to a channel-section framework, which is suspended in such a way that it can move freely in an axial direction, but is resistant to sideways movement. The suspension is by means of steel strips, by which the cradle is hung from heavy cast-iron pedestals. " To cater for cases in which the hot gases do not leave the jet- pipe in a truly axial direction, both sides of the cradle are con nected to its thrust-resisting levers; any difference in the forces on each side is compensated by coupling the two sets of levers together by a strong torsion-shaft. The final lever of the cradle is connected to the thrust-mea suring weighing machine by pull-rods. By suitable leverage ratios, the force reaching the weighing machine is reduced to one seventy-fifth of the thrust exerted by the engine. The thrust weighing machine itself is in the control room. It is an Averv pendulum (springless) weigher, and is connected to the final pull-rod lever by a length of high-tensile steel wire of only 5'32-in diameter. To check the accuracy of the readings, checking gear is provided bv means of which any desired thrust can be imposed on the cradle. This imposed thrust, applied by weights, is itself known with great accuracy, and thus the readings of the main weigher can be checked very closely. This checking process can be carried out verv quickly. Heenan and Froude were expected to ensure that any error in readings did not exceed one-tenth of one per cent at maximum load. This aim was in fact surpassed, and on a typical check test the average inaccuracy amounted to only 0.0225 per cent. The fuel-system main storage tanks, each holding 12,000 gallons, are sunk in a pit outside the test-house buildings. From here fuel is pumped to each plant by Wayne centrifugal pumps, driven by flameproof motors, and similar unloading pumps are also provided. The pumping system incorporates tank contents gauges, filters, recording flowmeters, and de-aerators; all this equipment has been supplied by the Wayne Tank and Pump Co., Ltd. Each test plant embodies a fuel cubicle, constructed in brick as part of the main building so as to enclose and isolate it as a safety precaution. Each cubicle contains a mild-steel structure carrying Rotameters for instantaneous readings of fuel flow, an Avery- Hardoll flowmeter with timing unit, and a Brodie-Kent flow meter for reheat-fuel flow. Negretti and Zambra dial-type mercury On each side of the main entrance to the Coventry test house are the Muffelite splitters; through these the air enters the two test-beds, which extend back on either side of the central control room.
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