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Aviation History
1963
1963 - 0839.PDF
Capt B. W. Gardiner, operations director of British United (CI) Airways, accepts a Handley Page Herald from D. A. Cashley, HP's assistant sales manager. This aircraft is the fifth in the former Jersey Airlines fleet and was the first to be painted ex-works in the operator s new blue and gold colour scheme AIR COM MERCE .. . WHAT ABOUT THE BOOM? THE most fundamental, yet so far unpredictable, aspect of super sonic commercial airliner operations is the sonic boom. For some time it has been thought that the effects of aircraft size and lift on boom intensity will not be known for certain until a big aircraft is flown. But even more difficult to determine is the safe and accept able pressure rise as far as things and people on the ground are concerned. Considerable research into sonic boom intensity and its effects have already been carried out in the United States and some of the preliminary results were summarized in a recent paper by Mr J. K. Power and Mr G. Bates of the Federal Aviation Agency. The theory for calculating ground level pressure-rises at high Mach number and high altitude requires complex mathematical analysis if full account is taken of aircraft shape and lift. However, with the aid of electronic digital computers, the theory has been calculated and has shown good agreement with practice in the form of tests using supersonic military aircraft up to the size of the B-58 at speeds up to Mach 2.0 and altitudes of between 30,000ft and 60,000ft. The size of concentrated booms due to the aircraft diving, turning and accelerating can also be analysed theoretically and NASA-USAF-FAA flight tests have shown firm confirmation here as well. Of the effect on buildings, the paper concludes that no structural damage will result within the range of pressures anticipated for the supersonic transport. The strain response on buildings of various kinds was measured and found to be negligible for those with sound primary structures. The sonic boom pressures anticipated for commercial airliners come much nearer the limit for windows and large unsupported panes of thin glass might break. Another series of tests was made to see if the boom pressure would damage light aircraft and helicopters, and it was concluded that there would be no damage up to overpressures of 201b/sq ft—well above the maxi mum of just over 21b/sq ft expected from a typical SST. The most important factor to be taken into account when deter mining permissible boom pressure intensity is, of course, com munity reaction. This is also the most difficult to assess. In the United States a considerable amount of statistics has already been obtained from interviews with residents living beneath a B-58 practice run. Public acceptance of the boom will vary with frequency, national temperament, and so on; and although this particular sample of public opinion was made after only 56 booms over a four-month period, the intensities were about those that an SST will make, and the results are useful for that reason. Each interview lasted over an hour and, to ensure unbiased responses, the residents were told that the questions were part of a general community survey and many questions about other local problems were asked. In the opinion of the trained interviewers, few residents suspected the true purpose of the study. Feelings of annoyance in the Metropolitan area studied were quite low; more than half of the people were not disturbed by anything and only one in five had any substantial annoyance. The rate of annoyance did not seem to change with small variations in boom intensity and the most disturbing features of the boom were put in the order: house vibration, startle, interruptions of sleep, rest, conversation, radio and TV listening. Residents were always warned in advance over radio and TV of practice runs and widespread understanding of the cause of sonic booms was found to minimize startle and reduce annoyance; over 90 per cent of the subjects gave good explanations of the cause of sonic booms. It was found that annoyance decreased where people felt that supersonic flying was important, and 90 per cent of those interviewed felt that military flights were important. Many of those who were not annoyed by the military booms and felt civilian supersonic flights were important said they can accept booms; a quarter of those who were annoyed likewise felt that they could live with civil booms. Work is still continuing in the United States on this problem, which is also attracting increasing attention in other countries. In a recent paper Mr Bo Lundberg, director-general of the Aeronautical Research Institute of Sweden, proposed a ten- point criteria for determining the acceptable level of sonic boom intensity:— (1) The acceptable sonic boom intensity must be based on more stringent considerations than those applied to airport noise. The areas that will be afflicted are incomparably bigger than These FAA curves from the paper abstracted on this page show the speed profile for a flight by a typical supersonic airliner and the boom over pressures on the ground directly beneath its track MS25 M-2.3 3.0 32.0 1 1.0- > o 4 ' IS KANGE-100MI. OVERPRESSURE UNDER FLIGHT TRACK "A A I 18 RANGE-10C Ml. 20 21
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