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Aviation History
1958
1958 - 0042.PDF
44 THOUGHTS on WS-110A A Mach 3 Bomber with a 6,000-mile Range THE photographs on the two preceding pages suggest thatthe U.S. Air Force (and, no doubt, the Soviet Union, isleading the world into a new era in which strategic bombard- ment will be conducted solely by hypersonic ballistic missiles. Such devices can lift a thermonuclear warhead weighing several tons to a height of 800 miles above the earth and carry it 5,500 miles at a speed fifteen times greater than that of sound. The logical conclusion is that when they are acceptably reliable they will make the manned bomber as dead as the dodo. But this is by no means the case. America's ICBMs will be operated by the U.S.A.F. Strategic Air Command, but this Command has no intention at present of dispensing with its aeroplanes—indeed it has stated that it will order two more generations of bomber to succeed its present equipment of B-47s and B-52s. There are many reasons for this policy. The most obvious JS that the ballistic missile can handle only a limited variety of mili- tary tasks. It is essentially inflexible in operation and makes military sense only when it carries a warhead with a yield of many megatons (limited only by the available payload), and its first cost —currendy put at between $lm and $2m when in full production— precludes firing against targets of secondary importance. More- over, as we pointed out in our "Guided Missiles" issue of December 6 last, the ICBM has not yet learnt to search for its target and so can be used only when the co-ordinates of its target are known at least to within a mile or two. Moreover, severe limitations will curtail the deployment of these weapons; their sheer size handicaps their transport to overseas bases and they can be fired only from mammoth fixed sites involving millions of cubic yards of concrete and underground catacombs, together with such associated paraphernalia as storage tanks for hundreds of tons of fuel and liquid oxygen. In view of these facts S.A.C. have sponsored the development of two piloted bombardment systems of very great importance, and there is also a good chance that they will operate the relatively short-range Convair B-58 Hustler (WS-102) which is already flying. Colloquially the two new strategic bombers are known as the C.P.B. and the N.P.B., these letters standing for chemical-powered bomber and nuckar-powered bomber. Their respective weapon system numbers are 110A and 125A. The latter is obviously a long-term project, and its endurance of at least one week will enable it to undertake missions quite outside the scope of any aeroplane at present flying. It will, for example, be able to adopt any desired night plan in attacking any target on the face of the globe. One such mission might involve flying right across Siberia at tree-top height at a speed very much greater than Mach 1, while another might be a standing patrol at great altitude for days on end undertaking some form of countermeasures in support erf other operations. Two prototypes to this specification are being built by Lockheed's Georgia Division, using a propulsion system by Pratt and Whitney; two more prototypes are being constructed by Convair at San Diego, using a propulsion system by General Elec- tric. One example of each aircraft is expected to fly next year. At the moment, however, the U.S.A.F. is more immediately concerned widi the WS-110A, which has been scheduled as a direct replacement of die B-52. Naturally the full terms of the specifica- tion have not been published, but they are known to include a cruising speed of the order of Mach 2 and a "dash" performance r/i;s model was recently seen in Boeing's super- sonic tunnel; it seems to be that company's WS-110A. of approximately Mach 3, or 2,000 m.pJi. This in itself is a severe challenge to any design team but it becomes almost impossible when coupled with the required range of 6,000 miles widiout refuelling. This range, which is comparable with that of the B-52s at present in service, must nevertheless be extended by air refuelling, in some cases on both outward and return journeys. To all intents and purposes the specification parallels that for a supersonic transport, and enough has already been written about the supersonic airliner to emphasize the magnitude of the problems involved. In our issue of February 8, 1957, it was \ pointed out that one of the key factors in the design of a supersonic- ' cruise vehicle is the achievement of adequate lift/drag ratio. Sub- sonic aeroplanes can cruise with a L/D of at least 16, but no wing has yet been found capable of flying supersonically with a lift/drag ratio of even half this value—in fact between 6 and 7 is at present regarded as die best that can be done. Assuming a specific con- sumption figure comparable with mat of the best current jet bombers, it follows that a given mission will demand more than twice as many B.Th.U.s as at present. If the subsonic and supersonic bomber were both to burn the same fuel the latter would clearly need to have more than double the tankage (irrespective of the arrangements for air-refuelling contained in die flight plan). Reference to die existing B-52 with its 40,000 gal capacity emphasizes the sort of aeroplane which results from a specification demanding a subsonic range of 6,000 miles; and it is unthinkable that any device could at present be built capable of cruising supersonically with twice as much tank- age. The "break-dirough" which has made the C.P.B. practicable is the evolution of entirely new fuels with appreciably higher heat-content per unit weight or bulk, so that the additional B.Th.U.s can be provided without significantly increasing the size of the airframe. These new fuels were discussed in general terms in our issue of March 15, 1957. This article mentioned some dozen types of fuel of several different families. Of these only the boron-based liquid propellants have so far been adopted by the U.S. Services; the specification for the U.S.AF. high-energy fuel has naturally no; been divulged, but it is known to be principally based upon pentaborane and to be already in bulk production at a plant near Niagara Falls, N.Y. These new fuels pose immense problems both in the design of die powerplants and owing to the fact that the exhaust is relatively toxic. In all probability die aim is that their use should be restricted to the "dash" part of a mission, although the 40 per cent additional range which they confer is so attractive that the ultimate WS-110A will certainly be designed to rely on high-energy fuel entirely. It should be added that the new fuels do not contain their own oxidant, so increase in a'.tirudc performance is restricted to that achieved by sheer speed. Nobody can reasonably plan an aeroplane until die basic para- meters of its propulsion system are settled, and so the "chemical- fuel" turbojets are being developed to a slightly earner time schedule than dieir associated airframes. Leading contractor in this work is General Electric. Indications are that the WS-110A engine will be a development of die J79 single-shaft turbojet, with variable stators and an advanced form of afterburner and fully- variable nozzle. If the aircraft were to weigh 450,000 lb it would probably require at least eight of these engines, each with a maxi- mum theoretical sea-level thrust of about 30,000 lb. Obviously the intake and duct geometry for the new bomber will have to be very carefully engineered for the great range of flight conditions. Turning to the aircraft itself, the requirement was written in 1955 and Phase I (study) contracts were placed with the Boeing Airplane Company at Seattle and North American Aviation at Los Angeles in die winter of 1955/56. Both companies seem to have made heavy weather of the assignment, and their initial pro- posals were refused by the A.R.D.C. Possibly anticipating funnel "break-throughs" leading to a substantial reduction in design gross weight, die U.S.A.F. ordered the companies to think again in the autumn of 1956. The sheer magnitude of die task of preparing the engine and airframe designs, coupled with increasing restrictions on research and development appropriations, have kept WS-110A Concluded on page SI)
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