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Aviation History
1957
1957 - 0175.PDF
8 February 1957 177 acceleration and slowing down. Aluminium and magnesium alloyssuffer drastic deterioration in their physical properties at about Mach 2, and after prolonged heating never regain their low-tem-perature properties. These materials must be abandoned, and replaced by steel and titanium. But it is very difficult to obtainefficient structures with such denser materials under compression loads (the stress-case which accounts for the greatest proportionof the weight of an aircraft structure). The use of titanium in honeycomb-sandwich form appears to provide the most promisinganswer on all counts, but it is an expensive material, and notoriously difficult to fabricate even in single-panel form.Titanium-sandwich airframes will take years of expensive research to perfect, and it is probable that the cost of their fabrication willbe several times greater than that of present-day structures. The Mach 2.5 transport appears to be ruled out as the first step incommercial supersonics; but it may well be the second step. Mach 1.9 The Right Choice? It remains to examine the possibilities of flying somewherebetween Mach 1.5 and 2.5; in other words to choose a speed which avoids the penalties of restricted range and low efficiencies on theone hand and kinetic heating problems on the other. Without a computer it is an arduous business to hit upon the optimum com-bination of all the variables: but, with non-stop transatlantic ability as the objective, it appears that a Mach number of ratherless than 2, say 1.9 (1,250 m.pJi. t.a.s.), may provide a good starting basis for further exploration. If a structure weight of40 per cent can be achieved, and a specific fuel consumption of 1.2 and an L/D of 8, then a payload of 8 per cent comes within sight.And if single-stop Atlantic operation were acceptable, a payload of 12 per cent could be achieved for the same drag, powerplantand basic-weight criteria. Such a transport would be expensive to operate—about 20 percent higher than the DC-8 or 707 assuming revenue to be com- parable. But the technical difficulties, though still formidable,might be capable of solution in the time. It is conceivable that a spirited research programme could, by the mid-sixties, find theanswers to the vicious-circle problems of: (1) achieving high L/D for Mach 1.9 long-range cruising while retaining perfect controlcoming in on a G.C.A. at perhaps 200 kt; (2) achieving low con- sumption without prohibitive powerplant weight and tempera-tures; (3) obtaining good field-performance without recourse to heavy powerplant-energized lifting devices; and (4) producingstructures more efficient than those of today to withstand the higher loadings, again in order to keep basic weight down. This is quite a catalogue of problems, but—with others toomany to recount here—they will have to be resolved before the dream of supersonic flight can come true. We shall preface our conclusions with the opinions expressedrecently by Lockheed and Douglas (see January 11 and 18 issues) on the subject of supersonic transports. Mr. Hall L. Hibbard,senior engineering vice-president of Lockheed said to Flighfs representative: — "I say that the industry—and I hope it is Lockheed—will have aprototype flying in eight years' time, and in operation four to five years after that ... I should say Mach 2.7 is about right. . . . We wouldhave plenty of power for take-off, plenty of wing for very-high-altitude cruise, and certainly blown flaps and reverse thrust for landing. . . .As for the thermal barrier, sure it's right there, but we will just fly above it at 100,000ft. The airplane will have to go some ways. Wethink everything is fitting into place just perfectly." By contrast, Mr. G. F. Worley of Douglas said: — "It appears that the short-range capability and the high operatingcosts of the supersonic transport, together with the small time-saving at the ranges for which a supersonic airplane is suitable, will limit theair transport field to subsonic aircraft through the 1960s. By 1970 tech- nical advances will probably justify beginning [our italics] the designand development of supersonic transport types, but it is not likely that they will be performing any important part in the transport economy." These are opinions expressed by firms of great repute, eachwith considerable practical supersonic experience; the fact that they differ so fundamentally is a measure of the problem. Some-one is right, someone is wrong; a fact of which we are aware in presenting the conclusions of the present study. Conclusions Our analysis of supersonic transport has been restricted to thebasic issues; but it is possible to conclude that, for the first step, the right choice of speed might be Mach 1.9, between Mach 2.5kinetic-heating problems and the low efficiencies of Mach 1.5. For non-stop Atlantic operation the payload would be small, say60 passengers, and operating cost 20 per cent higher than 707 levels. There might be a market for such a transport, if theimmense technical difficulties, i.e., the L/D, consumption and basic weight figures required, could be resolved in time for serviceby 1970. This means that a prototype should fly by 1965. Single-stop Atlantic operation would not be acceptable at thisspeed; but for medium-haul (say 1,500-mile) routes a Mach 1.9 specification might be devised to offer, by 1970, 100-passenger-plus payloads and an economy competitive (but not comparable) with subsonic jets. There would appear to be a probable, iflimited, market for such a machine. Finally, it appears that commercial supersonics may not becomeestablished until speeds of at least Mach 2.5 can safely be achieved —perhaps, with an all-out effort, in under 20 years' time. As Sir Arnold Hall said in his review of the subject in his recentWright Lecture (Flight, December 28, January 4 and 11): "It would be imprudent to suppose that [Mach 2.5] could be reachedquickly without substantial experience in this regime of flight." FOUR NEW SHAPES IN THE GUIDED-MISSILE FIELD On p. 167 some information is published relating to new types of American missile or test vehicle. These are the devices in question. At lower left is the Martin/Cornell Laboratory Lacrosse on its launcher; next above is a North American X-10 test vehicle landing at Patrick A.F.B.; on the right is a Lockheed X-17 research vehicle being fired at Patrick; and at the centre, below, is a Bell GAM-63 Rascal, the present standard U.S.A.F. air-to-surface nuclear missile, mounted on its ground-handling vehicle at Holloman Air Development Center, New Mexico.
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