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Aviation History
1957
1957 - 0511.PDF
FLIGHT, 19 April 1957 513 but neither the gun nor the air-to-air missile could lightly bediscarded. The Air Force were anxious that the supersonic intercepter should employ a guided air-to-air missile and, in viewof the long-term nature of the programme, it seemed practicable to design the aircraft simply as a carrying vehicle for such aweapon. In order to develop a complete integrated weapon system—a concept which was then (1950) beginning to be appreciated—the Air Force first held a design competition for a complete fire-control system (MX1179) for such an intercepter. The purpose of this mass of electronics would be to insure the success of eachmission, by putting the aircraft in the right place at the right time, and pointing in the right direction, and then launching its arma-ment automatically. The winners of the MX1179 contest were Hughes Aircraft, of Culver City, who were accordingly askedto undertake complete development of the system. Seven years ago the U.S.A.F. had no guided air-to-air missilearound which the company could develop its ideas, and Hughes accordingly determined the form which the weapon should take.In view of the anticipated high performance of the carrying vehicle it was decided to give the missile the highest possiblespeed, at the expense of range. This led to the concept of a very small missile, powered by a solid-propellant motor with a burningtime of only 1| seconds. General Electric had been developing such a missile under the project-name of Dragonfly, and Hughesrevived this abandoned programme and used it as a basis for a complete air-launched missile system under the fighter-typedesignation of XF-98 Falcon. As described in our issue of December 7 last, Falcon is now widely used in the U.S. Air Forceas the GAR-1 (guided air rocket). It weighs just over 100 lb, has a 6,000 Ib-thrust motor and is a beam-rider with terminalhoming. Later models, now in production at the Hughes missile plant at Tucson, have infra-red homing. When, in 1951, Hughes were confidently able to predict thecharacteristics of the final Falcon missile and its associated MG-10 fire-control equipment, the Air Force asked airframecompanies to submit their ideas for a machine to carry them. Each firm started off by attending a Hughes symposium on the weaponsaspect of the system. Convair won the competition with, their delta-wing project, and detailed design was initiated as theConvair Model 8 (U.S.A.F., XF-102). As far as possible, the new machine was a direct scale-up of the 7002, to a linear ratio ofabout 1.22. The original design gross weight was about 30,000 lb, and the engine chosen was the Pratt and Whitney J57 two-spoolunit, which was then running in experimental form. Long before the fire-control and missile were anything like ready,Convair had finished the design of the Model 8. Although a direct scale of the Model 7002, its lateral intakes gave it a different appear-ance, and in detail it was a largely redesigned aeroplane. In view of the U.S.A.F. requirement for well over a thousand F-102s (i.e.,this was the potential market), Convair decided to employ construc- tional methods suited to a long run at a high rate of production. A particularly fundamental outcome of this doctrine was theadoption of an exceptional proportion of forged parts. The U.S.A.F. heavy-press programme (which then stood at $389m)was relied upon to deliver complete fuselage frames, wing spars and longitudinal members—•& total of eight types of part—alldesigned to be pressed from single large forgings. Such a decision reduced the weight of each aircraft by over 100 lb, and saved 273components and 3,200 rivets. Alcoa and Wyman-Gordon were made chief "heavy-pressers." Another fundamental factor wasthat the Convair intercepter was the first aircraft to be planned for production under the Cook/Craigie plan. Generals Orval R. Cook and Laurence Craigie were the jointauthors of a scheme suggesting an idealized production cycle for U.S.A.F. weapon systems. From the drawing board, productiontooling would be installed with a capacity for production at the maximum rate envisaged, and it would then be used for themanufacture of a progressively accelerating flow of aircraft. The first machine, for example, might be followed by the second onemonth later and by the third a week after that; after three months the delivery rate might be six per month, perhaps rising to 60 petmonth a year later. Such a scheme was intended to permit inten- sive test flying with an increasing number of aircraft to uncoverall the major "bugs" before the production flow accelerated to the final torrent. By 1952 Cook/Craigie ideas were guiding manyAir Force programmes, but the 102 was tied to the concept from the beginning. Convair could not have foreseen how importantthis fact would become. By overworking some San Diego departments, the first YF-102(serial number 52-7994) was ready for trials in the autumn of 1953. It was trucked to Edwards, and there flown by R. L. (Dick)Johnson, chief engineering test pilot, on October 24 of that year. Most unfortunately, it suffered engine-failure at take-offon November 2 and was damaged beyond repair in the subsequent emergency landing. It was not possible to continue flight trialsuntil the second machine flew on January 11, 1954. Thereafter the test programme progressed normally until the flight envelopewas pushed out horizontally towards the transonic regime. Over a period of a few ghastly days in the spring of 1954 it became clearthat tunnel results had been optimistic, and that transonic drag of the YF-102 was greater than the available thrust. In otherwords, Convair's supersonic intercepter was subsonic. This put the whole programme in jeopardy. The Air Force hadstipulated a supersonic Mach number in the original specification, and complete failure of so fundamental a nature was sufficientground for cancellation of all the contracts placed. The YF-102 was already equipped with the biggest and most powerful flight-cleared engine in the western world. Somehow drag had to be reduced and by a wide margin. Fortuitously, salvation was immediately at hand. AttheN.A.C.A.Langley laboratory a team under Richard Whitcomb evolved the area rule (Flight, September 30, 1955), a simple empirical lawwhich, if properly applied to aircraft design, results in minimum transonic—and supersonic—drag. Convair's aeroplane did notconform to the rule, and the manner in which they made it do so, and the improvements which resulted, are now a classic in theannals of aircraft design. It was obvious from the start of the task that redesigning theairframe was going to be a major undertaking. Having several months thus occupied, the company decided to see in what otherways their intercepter could be improved. The YF-102 was not really an inspired design. It was builtlike previous aircraft, large assemblies being erected to form a virtually complete airframe upon which several thousand man-hours then had to be expended on the installation and testing of sundry details, systems and equipment. Much of the interiorwas unduly inaccessible, and many of the most important main- tenance or replacement tasks could not be undertaken withoutfirst removing the complete powerplant. Moreover, pilot view had been found to be inadequate, especially at extreme angles ofattack. Convair pulled the whole design apart and, by re-engineer- ing the aircraft in more intimate co-operation with the shop floorand the customer, turned the 102 into an excellent combat weapon and a production engineer's dream. Superficial changes to reduce transonic drag involved majorrevision of the fuselage profile to give reduced cross-sectional area over the wing and the filling-in of the area diagram by the additionof huge bulged fillets flanking the jet-pipe and propelling nozzle. The wings were given partial conical camber (progressive increasein leading-edge camber from the root to near the tip, giving a marked negative-incidence entry over the outboard portions) toreduce drag at high altitudes and to improve behaviour at high angles of attack. The fuselage was greatly lengthened and the nose 6682 Top to bottom: The XF-92 Model 7002 (46-682) as originally built; the first YF-102 (52-7994); and the first area-ruled YF-102A (53-1787).
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