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Aviation History
1956
1956 - 0931.PDF
VALIANT SILENCER AT the Anglo-American Conference last year Mr. E. S. Allwright,•**• deputy assistant chief designer of Vickers-Armstrongs (Air- craft), startled delegates by projecting a slide of the strange deviceillustrated here. It was the first public showing of the silencing equipment which his company has developed to muffle the blastof the Valiant medium bomber (four Rolls-Royce Avon). Since that time there have been several development problems,but the equipment has been in full use since February and is now quite trouble-free.Gas-turbine-powered aircraft do not usually have to do much ground running except during the testing and calibration stage atthe start of their life. The Valiant starts life at Weybridge, Surrey, in the centre of what was once Brooklands motor-racing track.Within the periphery of the old track site the whole space is now almost filled by design offices, production plants and other typicalramifications of a great aircraft company 3 with room in the centrefor what must surely be the tiniest large-jet-bomber airfield in the world (out of which the newly built Valiants have to fly). Theinevitable result is that opening up the quartet of five-figure- thrust Avons used to cause quite a lot of distraction to most ofthe Weybridge staff, and also threatened to impair the company's good relations with the residents of a heavily populated surround- ing district. It was a problem which had to be solved in good time.In 1954 it was decided to build silencing equipment. Owing to the size of the Valiant a static pen would have been impracticableand accordingly a portable silencer—necessarily of awesome dimensions—was evolved. The unit comprises paired circularintakes, a common conical diffuser and a final splitter box in which most of the muffling takes place. The splitter box is 15ftin length and contains conventional splitters, six inches thick, filled with sound-absorbent material. The whole unit is pivotedhydraulically about vertical and transverse axes to a girder chassis fitted with aircraft-type wheels, with hydraulic brakes to hold theunit against the end-load caused by the gas flow. Owing to the different heights of the Valiant's inboard and out-board engines (see photograph above) there are separate left- and right-hand silencers, which are towed into position by a tractorbefore any ground-running takes place. Measurements taken by the National Physical Laboratory show that at a distance of 100ydthe silencers cut the noise to the rear of the Valiant by some 20 db at maximum power; this is roughly the same as the noiselevel at the front caused by the main engine intakes. It is fair to state that Valiant running now causes no disturbance to anyonenot in the immediate vicinity of the aircraft. As far as can be ascertained, this is the first portable silencer for large jet aircraft yet to go into use anywhere in the world. The design was carried out by Vickers-Armstrongs and the manufacture was entrusted to the Elswick (Tyneside) works of Vickers-Armstrongs (Engineers), Ltd. Cooling is effected solely by the airflow induced by the jets from the twin Rolls-Royce Avon turbojets.
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