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Aviation History
1962
1962 - 0510.PDF
508 FLIGHT International, 5 April 1962 Al R COM M ERCE... Fig 2 The sonic-bang carpets which could be expected over the North Atlantic and Europe if transatlantic supersonic civil aviation were introduced. Carpet-width shown is 90 miles radiation at supersonic flight altitudes, at least if one considers even moderate effects due to solar flares. This might seriously affect the acquisition of female passengers and crew members. For such reasons it appears that the knowledge available today about the damage and hazards due to cosmic radiation would suffice to justify calling-off supersonic aviation on this ground alone, as long as restriction of the operation to below about 40,000ft is not conceivable. There would be reason to change this conclu sion only (a) if and when the scientists find that the present indica tions are wrong and that the radiation hazards are negligible, or (b) an invention has been made that efficiently protects the occupants of an SST. Safety with Heated Structures The heated structures of the SSTs will be subjected to much more complicated and varying tempera ture/loading histories than subsonic-aircraft structures. To ensure the same safety level with a weight-efficient structure subjected to elevated temperatures*, it would thus be necessary to obtain a much greater amount of information for the stressing of SST structures. This will, however, hardly be possible even in decades of testing, because of the fact that the testing time cannot be "compressed" when elevated temperatures are involved—as opposed to fatigue testing of "cold" structures, where high-speed fatigue machines can be used. For these reasons, the design of SST structures will be subject to much greater uncertainties than subsonic ones, and it seems very difficult indeed to compensate fully for this. On the basis of present knowledge and normal advances it therefore seems hardly possible to attain the same fatigue safety level for an SST structure as for contemporary subsonic aircraft, even at the expense of such weight penalties and/or with such short inspection intervals as are likely to render the SST economically unfeasible. On the basis of the foreseeable increase of knowledge and normal technological advances, each of these three technical problems appears to constitute an insurmountable obtacle—the sonic boom and cosmic radiation problems perhaps indefinitely, aerodynamic heating for at least some ten years. Even if two of these obstacles could be overcome, the SST would still not be feasible. Profitability of the SST It is important to realize fully the impli cations of the fact that the subsonic airliners, with which the SSTs will have to compete, will undoubtedly display successively re duced operating costs, particularly after introduction of BLC technique. The conclusions I have come to are: (a) that for SST to be reasonably certain, during the next three to four decades, of attracting a major portion of subsonic aviation on typical SST ranges, the design must be so advanced that it will show much lower operating costs than the present jets: and (b) that this, for operation over the Atlantic and similar route systems, has to be achieved with an appreciably lower annual utilization and/or lower load factors than the competing subsonic jets are likely to enjoy. The reason is that it does not seem possible to achieve convenient departure and arrival times for the additional number of flights that an SST must produce in order to obtain the same utilization in flight hours as subsonic aircraft. Thus, even disregarding completely the three basic technical * In this context elevated temperatures are defined as temperature levels that, for the Mach number I material combination applied either cause noticeable impairment in the static, fatigue, crack-propagation and/or elastic properties of the material, or appreciably change the load distribution, in fail-safe redundant structures due to creep. problems, it seems obvious that the operators would take a very big risk by ordering SSTs before the manufacturers could offer designs which are much more competitive with regard to operating cost than has been indicated up to now. Since the profitability of the SST can thus at best be regarded as marginal, in view of the competition with the subsonic jets, even a moderately adverse effect of any one of the three basic problems—be it operational restrictions due to sonic boom and cosmic radiation, reduced passenger appeal because of fear of radiation, or economic penalties due to heated structures—could easily make the operation entirely uneconomic. As there now seem to be hardly any prospects of any of the three main problems being solved within some ten years the operators have to consider the combined effect of these three problems on the basically questionable profitability of the SST. In view of this it seems hardly conceivable that any operator who has thoroughly studied the whole problem would gamble on ordering SSTs until not only the profitability prospects were much brighter than present indications but also until the three basic problems had been solved. The great risk confronting civil aviation right now is, neverthe less, that one or two airlines might order a number of SSTs in order to be first in a "supersonic race," because then it is quite probable that a number of others would follow suit; in other words, there would be a chain reaction similar to that when the subsonic jets were introduced. If this occurs, civil aviation would blindly and against its best interest have become inextricably involved in a situation which can be regarded as nothing less than disastrous, not only because the SST part of civil aviation would be subjected to heavy losses but also, and even more important, because the much greater subsonic portion of aviation would suffer badly. It would thus be in the best interest of aviation to prevent such a development. To be concluded Fig 3 A similar picture for North America, again with a carpet-width of 90 miles
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