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Aviation History
1978
1978 - 0084.PDF
114 Letters Fatigue analysis: don't blame the tools SIR—Everyone will support W. G. Heath's call (December 10) for a more effective fatigue-damage measurement hypothesis, and might be forgiven for looking towards the experienced fatigue analyst as one of the most likely sources. By their very nature, hypotheses are always vulnerable to criticism and calls for change, and recent fatigue failures do suggest the possibility of a radical review of generally accepted concepts. The fatigue analyst can now explore more sophisticated forms of data recording, which allow loading events to be identified with particular conditions of aircraft weight, trim and configuration without recourse to laborious studies of trace recordings. Extended digital recording and real time data processing are available in the new generation of fatigue load- meters now in production for military aircraft. The established fatigue load-meter —so called because it is something more than a counting accelerometer, in that its counting methods and res ponse to acceleration events have been carefully matched to our present knowledge of the fatigue problem— does produce a usable life estimate based on the Range Mean Pair count ing philosophy. I am sure that Mr Heath would allow that this device, which implements the present popu lar philosophy with remarkable reli ability, is better than nothing at all and will long continue to make a significant contribution to air safety. Counting extensiometers are still used and remain available in a form which avoids the use of strain gauges and their particular calibration prob lems. While presenting large long- term maintenance problems more associated with the installation than the equipment, these strain-range re corders are a recognised practical alternative only when other data sources represent an unacceptable compromise. D. P. GREENGRASS Negretti & Zambra (Aviation), 73-77 Lansdowne Road, Croydon CR9 2HP Battersea in the doghouse SIR—I wonder whether in his haste to put pen to paper Mr Cater of Bat tersea Heliport (Letters, December 17) found time actually to read the report on helicopter noise in the London area prepared by a working group of the Noise Advisory Council. To set the record a little straighter, the members of the Council are not Civil Servants. We are an indepen dent body appointed to keep under review the progress made generally in preventing and abating noise. This is why we have taken an interest in helicopter noise, which, unless we take steps to anticipate events, could become a very much bigger problem than it is at present. I find Mr Cater's letter a little puzzling, as in the preparation of our report we received valuable advice and assistance from Westland Heli copters Ltd. This is clearly acknow ledged in the report. When we met Westland's chief scientist and man ager they advised us that at Batter- sea helicopters generally approached on a 3° glideslope. Perhaps the CAA tests of an 8J4° approach are more recent, but in any event this is noth- Correspondence for these pages should be addressed to the Editor, Flight International, Dorset House, Stamford Street, London SE1 9LU, and marked "For Publication." Letters should preferably be no more than 300 words long. We reserve the right to edit all correspondence. ing like the 30° approach which we have suggested. The map accompanying our report makes it clear that the routes do make use of existing and proposed motor ways and other roads as well as the River Thames and other open areas. We have suggested that if pressure for heliport facilities continues to grow, the possibility of diverting traffic to a site farther east should be examined. There is likely to be traffic from the north and south which could transfer and thus avoid flying through central London, with consequent benefits to the people working below. I noticed Mr Cater's uncharitable reference to Wandsworth Borough Council. Might it be that this auth ority is concerned at the way the operators of Battersea Heliport have disregarded planning conditions on the maximum numbers of permitted movements? Norwood Hill, ERIC EPSON Horley, Surrey Metric mix-ups SIR—I am not qualified to discuss the merits of the metric system as com pared with Imperial, but when metri cation creeps into practical flying I am getting very anti. While the fact that the bowserman sells me litres which I have to enter in the loadsheet as pounds and in the Customs drawback form as Imperial gallons is ridiculous but tolerable, the promulgation of weather elements in FLIGHT International, 14 January 1978 metric units is downright dangerous. When Prague Tower told me that the wind was 6m/sec at 200°, how was I to know whether this was dol drums or gale, or inside or outside my crosswind limitation? Similarly, ceil ings given in metres by terminal in formation services (France and Bel gium) are useless for a pilot with approach plates and decision heights in feet. But there is worse to come. A reader's letter in last August's Business Aviation is worth reading in this connection. The writer suggested that pilots should throw the towel in and accept metrication as inevitable. His solution for vertical separation was: "One altimeter revolution equals one flight level, regardless of the instrument reading, with an un changed vertical separation of 1,000ft equals 304-8m." Instead of Flight Level 230 we would have to file New Flight Level 70-104. This is as ludi crous as the abolition of the tailor- made nautical mile. CAPT ERNEST STOGMULLER Luton Airport, Luton, Beds Sunny spacewalk SIR—The article describing the Salyut 6 spacewalk (Flight, December 31, 1977) states: "The EVA was clearly timed to coincide with the passage of the spacecraft over the Soviet Union ..." and "... it took place after midnight, obliging the cosmonauts to work in darkness." Both of these statements are at variance with the truth. I have computed the following data from my own observations of radio signals from Salyut and com monly available orbital information. The Novosti press agency's London office states in a release that the hatch was opened and Grechko began his EVA at 0036hr Moscow time on December 20 (2136hr GMT on Decem ber 19). At this time Salyut 6 was over 158° West 20° South, with the Cook Islands in the South Pacific directly below. The local time was just after llOOhr, so the sun would have been nearly overhead. Twenty minutes later, when Grechko went back inside, Salyut 6 was over Santa Cruz in the Argentine at about 69° West 50° South. The local time would have been about 1700hr. Salyut 6 entered the Earth's shadow about 12min after this. The actual spacewalk thus took place in full sunlight over the Earth's southern hemisphere and was com pleted some 35min before Salyut 6 passed over Soviet territory. ROBERT CHRISTY 41 Meadow Lake Crescent, Lincoln IN BRIEF WO Ian Donaldson of No 142 Sqn ATC wants to know if there is a No 142 Sqn RAF association. Please address replies to WO Donaldson at 7/8 Broomview House, Sighthill Wynd, Edinburgh; telephone 031-443 4867.
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