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Aviation History
1961
1961 - 0718.PDF
728 FLIGHT, 25 A/c SUPERSONIC SYMPOSIUM . . . parts might limit the steel-titanium aircraft to Mach 2.75. and even thisspeed would involve problems in both these fields. The step from today's speeds to Mach 2, it was argued, was actually less than from Mach 2 toMach 3. To provide Mach 3 speeds, governments might be called on to provide many extra millions of dollars. (3) The Mach 3 steel-titanium aircraft. The case for this, like the othertwo projects, was prepared by its supporting manufacturers and read by the symposium chairman before going forward to the full technicalcommittee. The American case was that this aircraft would involve little additional research for the same flying qualities as slower aero-planes and would be favoured by range and efficiency factors. It was argued that there is actually more experience already in the use of steeland titanium for Mach 3 than for aluminium at Mach 2, although considerably more time-temperature work was needed for both con-cepts. Development work by the USAF was generally aimed at Mach 3. The sonic boom problem might dictate that the transonic stage wouldhave to be at altitudes above 40,000ft, and in this case Mach 3 was a more suitable figure. Such an aircraft would have a long service lifeand with new engines could move to almost Mach 4. Speed would more than offset the higher costs associated with materials develop-ment and up to a 20 per cent advantage in d.o.c.s or return on invest- ment appeared probable. Development problems could be solved in time for a 1970 aircraftand it was believed that customers were willing to wait until then. Growth capabilities were important, and were believed to favourthis project. Without extensive new development, a Mach 2 airliner's future growth would be limited to Mach 2.5. Development of a Mach 3design was a certainty, and hence the life of anything slower would be limited. It would be unwise to engage in a light-alloy developmentprogramme in view of the danger of early obsolescence of the materials. A steel-titanium structure would be as good from a cost-weight view-point, or better. No attempt was made to reach any decision on these competing outlooks and the final statements of philosophies read from the chair were not discussed by the symposium. Earlier, one manufacturer had told the meeting that entry of two constructors into the field, assuming they shared the market equally, would increase the purchase price of the SST by 20 to 25 per cent. No one disputed the statement. Elevating the Pilot A great deal about the SST itself emerged at the symposium. It will be from 185 to 200ft long, with a delta wing incorporating a straight or nearly straight trailing edge and 50° to 55° sweep on the leading edge. The nosewheel will probably be about 85ft aft of the nose, and the main landing gear will probably be double tandems. Various pilot 'positions have been considered, some as unortho- dox as a gondola to be lowered between the main landing wheels for ground manoeuvring, take-off and landing. It seems, however, that the pilot will actually sit about where he does today, although some 40ft in the air. His height from the ground, coupled with the nosewheel distance from the nose, were considered likely to make taxying somewhat more difficult than it is today. Various tail- plane arrangements have been considered, with a canard the most likely. Engines may be either fans or turbojets, depending on a combina- tion of factors including the boom problem, other noise considera- tions and the power needed for the subsonic to supersonic accelera- tion. Their thrust probably will be in 20,000-30,0001b range, pos- sibly as high as 35,OOOlb; and if the transonic stage has to be carried out as high as 5O,O00-55,O0Oft water injection may have to be provided. There will be either four or six engines and, although none is ready today, several are well along in the development stage and their manufacturers do not foresee any insoluble problems of materials. The engines may be either clustered in a buried mounting or be pod-mounted, but in either case they will be well back and con- siderably higher from the ground than today's engines—probably about 10ft. They will have variable-geometry intakes and possibly outlets, although the latter is considered much less certain. Tail- pipe thrust-augmentation may be necessary for the transonic stage, but its use on take-off is not envisaged. Engine pressures will be lower and temperatures and specific fuel consumption higher for the take-off, climb and acceleration phases. The variable-geometry intakes probably will be automatically controlled, but manual override will probably be needed. It was unanimously agreed that windows in the passenger cabin will be a requirement and that they will be much smaller than most of today's, and probably round. They may be augmented by closed-circuit television or "fibre optic" devices. The pilot will certainly have direct forward vision during taxying, take-off and landing, but not necessarily during supersonic cruise. It was argued that forward vision will not be necessary at cruise altitudes and that the actual requirements can be met by closed-circuit television or fibre optics, perhaps thereby actually improving visibility. Passenger doors may be wider to speed up loading and unloading, since ground time will assume increased importance a increase. Today's loading stairs may not be high enough more efficient and more easily loaded galleys will be highly iesirahiSome manufacturers would like to adopt five-abreast seatina m ?!?' first class, but the airlines were strongly opposed. Si\-a| economy-class seating was considered acceptable. A cei'ti need for first class, although as a steadily decreasing prop rtjmw | the whole, was foreseen. Manufacturers warned that volume may h I extremely costly to provide in first-class cabins. ' Flight frequencies will probably have to go up rather than dow and this problem will move closer to present short-haul requir" ' ments, for it appears established that, as journey-time drops th passenger expects a better choice of frequency. One airline said I had calculated that on a North American transcontinental rout where three jet frequencies were adequate today five SST frequen-T would be demanded. "tN Question of Range Discussion of range centred mainly around the two long-ran& '• projects and there was wide agreement that optimum figures will be dictated by North American transcontinental and transatlant'1 requirements. A 3,500-mile range was put forward as likely it would permit direct services from the US east coast to West European centres. This would be too short for direct trans Pacific operations, but it was felt that these would be carried out on a refuelling basis by supersonic transports rather than be left to the I subsonic jets. There were suggestions, however, that a 3.500-mile I range would impose some limitations on the size of the market for' an SST and even more agreement that a 5,000-mile range would both increase the cost seriously and limit the market even m. Various sizes were discussed, typical capacities being taker 85, 125-135 and 200 passengers. Manufacturers indicated that the old rule "the bigger the aircraft the cheaper the seat-mile cost" wii: still hold good—perhaps even more so than in the past—but thai over-capacity would be a serious problem and would cause schedul- ing difficulties. The 200-passenger aeroplane would cut frequencies even or high-density routes to a possibly unacceptable degree, and would rule it completely off many routes of SST range, both through traffic and airport limitations. One manufacturer suggested a j gross weight of 350,000 to 400,0001b for a 130-passenger aircraft, | and there was agreement that maximum gross weight in relation to payload will be greater than with today's jets. About one-half of take-off weight will be fuel. Discussion of a variable-geometry wing involved problems of I weight and complexity but there would be low-speed-handling | advantages. Ditching characteristics, a problem because of I approach-angles and speed, would be improved. Once successfully! ditched, the SST should have better bouyancy characteristics, bin passenger evacuation may be more difficult after any emergency; \ and cutting into the fuselage may be difficult with titanium, because • of the problem of sparks. Rear mounting of the engines should reduce fire hazards in a crash landing. On the other hand, some of the fuel will be carried in the fuselage, although there is a hope among manufacturers that large quantities can continue to be stored in the wing. It may be necessary to use liquid nitrogen to render inert the vapour areas in the fuel tanks. Structural Materials The problem of the limited selection of materials for a super-1 sonic transport, because of aerodynamic heating, was discussed' initially in the context of the probable total life of the vehicle There was general acceptance that the minimum target should be _ 30,000 hours, although a possible 40,000-hour life was suggested as • possible with a considerable increase in cost. Some manufacturers w suggested that it may be necessary to design for 50,000 hours in order to guarantee 30,000. Presuming a structural life of 30,000 hours, it was felt thai aluminium materials will not be satisfactory where temperature of more than 250°F are encountered. This would represent a limit of about Mach 2.4 in terms of leading-edge temperatures. « At Mach 3 a temperature of about 500° could be expected and at Mach 3.5 about 65Oc to 700°. It was recognized that there is little information on the behaviour of metals subjected to high tempera- tures for periods of more than 1,000 hours. Even this limited infor- mation deals mainly with unstressed test specimens and there i» an accompanying need for more information on the behaviour ot the materials to be used at the low end of the temperature scale, especially in relationship to crack sensitivity. The limiting enecft of the non-metallic materials used, especially rubbers and sealaIr was also accepted as an important factor. In addition, it would necessary to take into account the behaviour of the materials i relation to the type of structure in which they were used. Manufacturers felt that although a heavy amount of work remai. i to be done in this field the materials will be available in time tor m , SST. Engine makers shared this view so far as their metallur;
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