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Aviation History
1949
1949 - 1777.PDF
and •.,.'•.: AIRCRAFT ENGINEER First Aeronautical Weekly in the Worid Founded 1909 No. 2131. Vol. LVI. THURSDAY, 27 OCTOBER, J949. EDITORIAL DIRECTOR G. GEOFFREY SMITH, KB.E. EDITOR MAURICE A. SMITH, D.F.C. ASSISTANT EC/TQ8 ' H. F. KING, M.B.E. ART EDITOR JOHN YOXALL Editorial, Advertising and Publishing Offices : DORSET HOUSE, ' STAMFORD STREET, . '„; LONDON. S.E.I. •.,••>-'•' Telegrams : Flightpres, Sedtst, London. Telephone ; Woterloo 3333 6Q fines). Branch Offices : COVENTRY 0-10, Corporation Street. Telegrams : Autocar, Coventry. Telephone : Coventry 5210. BIRMINGHAM, 2. . King Edward House, New Street. Telegrams : Autopress, Birmingham. Telephone : ftUdland 7191 (7 lines). MANCHESTER, 3 2(0, Deansgate. Telegrams : Wife. Manchester. Telephone : Blatkfnars 4412 (3 lines). Deansgate 359S (2 lines). GLASGOW, C.I . 26b, Renfield Street. Telegrams : Iliffe. Glasgow. Telephone : Central 4857. SUBSCRIPTION RATES Home : Twelve months, £3 Is. Od Six months, £1 10s. 6d. Overseas : Twelve months, £2 18s. 6d. BY AIR : To any country in Europe (except Poland). Twelve months, £5 Is. Od. Six months, £2 10s. 6d. Canada and U.S.A. Six months, SI6 In this issue: Flying to the Limits - 542 Inside the Comet - - - 548 Htwgarian Revival - - S52 •*No Airscrew Fitted . ." 553 Beech Twin-Quad Power Plant 559 Drop, mod el Tests - 567 The Noise About NoiseF ROM the very numerous and verbose letters on abatement of noise in the air which have appeared in the London and provincial Press over a period of years, it has never been entirely clear whether the authors wish to advocate silent aircraft or the removal of airports from the vicinity of their own homes to a place where they would disturb someone else instead. The second alternative is as selfish as the first is unpractical. The suggestion thai aircraft should be stopped from flying along the many approach lanes to London's airports, and the airports themselves located out in the country, is somewhat reminiscent of the king who got his feet wet while trying to keep the beach dry. The most recent spate of correspondence in The Times and elsewhere is but another eruption from an old volcano. At an airfield thirty miles from London, one wall of a hangar is well on the way to being papered with plaintive letters clipped from the local Press. In this particular case a number of people, many of whom became residents long after the airfield was established, find that the Tiger Moths fill the air with loud noises and ruin their quiet week-ends- The fact that the young pilots forgo a quiet week-end in order to be prepared in emergency to defend that same air is conveniently ignored. A straightforward request for a reduction in noise of commercial aircraft, not only at London Airport but also at every other city boasting a busy airfield, is reasonable and merits full attention. The noise of an airliner to those outside it is a real problem and should receive as much consideration as the silencing of the cabin for those with- in. The most disturbing sources of noise are the airscrews. During the war the Harvard trainer was the worst offender, and most people sympathized with the residents of Grantham, for example, when they suggested after several years that they had had their share of this particularly shattering racket. Fortunately, by keeping down the r.p.m. and especially the tip-speed of an airscrew, the noise can be held within bounds. Power units themselves are more difficult to silence. Almost any form of silencer in the exhaust system produces back pressure, and this in turn leads to a reduction in power. For take-off a heavily-loaded commercial aircraft needs every scrap of power it can get. Silencing devices which do not adversely effect the power output are altogether too large for an aircraft to carry. Had this problem been tackled gradually over a long period, at least a partial solution might have been found, but, as Sir Geoffrey de Havilland has pointed out, we fly with engines, developed in the first place for war, in which performance counts above all else. The continuous noise of the exhaust or efflux from a gas turbine is a great deal less penetrating and disturbing than the pulsating sound produced by a piston engine, but again a practical means for silencing it is hard to find. It may be recalled, how- ever, that in the experimental Metrovick F/3, a'turbojet with ducted-fan thrust augmentation, an annular jet of cold air from the fans surrounded the hot jet from the turbine, and that this was found to have a marked silencing effect. In addition, there are means whereby particularly troublesome frequencies in the noise of a jet can be altered or eliminated. The high-pitched whine of the compressor—more audible in some units than in others—is almost impossible to shut in. There are certain facts, however, which point to a reduction in the noise nuisance in years to come: turbo jets are quieter than piston engines of comparable power; axial-flow compressors are quieter than the centrifugal type; jet-powered aircraft climb faster, both in rate and forward speed, and so are out of earshot more quickly ; they also operate normally at very' high altitudes and are thus almost inaudible in transit; and jet-powered airliners will not be stacked over airfields. It is unfortunate, but seemingly unavoidable, that houses should be built right up to the boundaries of airfields, for until aircraft are able to descend and ascend vertically they must pass low over some roofs. As one newspaper reader says, " It is an estab- lished fact that to disembark passengers, a modern aircraft must approach the ground sufficiently closely to enable those passengers to step down without injury." E I
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