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Aviation History
1957
1957 - 0510.PDF
512 CONVAIR F-102 An Analysis of America's Home-defence Intercepter By THE TECHNICAL EDITOR FROM many aspects, Convair's history of delta-wingintercepter development is a story of exceptional interest.Much can be learned from an overall survey of how the concept grew and developed, what sort of weapon system hasresulted and how it is built and operated. Briefly, the story is that of a futuristic conception, a massive research programme intounknown realms of aerodynamics, gradual translation into an integrated intercepter system, disappointing flight trials, com-plete redesign to turn an indifferent aeroplane into a very good one and, finally, a programme of development and productionwhich is a text-book model of perfection. Upon the Convair F-102 devolves a weighty responsibility.Its mission is a cut-and-dried one : to intercept and destroy, under any operational conditions, any enemy aeroplane which mightcross the American frontier. These words come readily enough from the pen; yet twelve years ago—when the U.S. Air Force'sstandard all-weather and night fighters were the piston-engined Black Widow and Twin Mustang—such a specification seemedunattainable. The jet bomber and the nuclear weapon multiplied the problems of nation-wide defence a thousandfold. Such were the problems posed by the new situation that, eventhough the keynote of the period was a run-down of military forces, the U.S. Defense Department originated a specification foran intercepter with a performance surpassing that of any previous piloted aeroplane. The requirement resulted in the ConvairCompany (now a Division of General Dynamics Corporation) receiving an Air Force assignment to develop such an aircraft.The first contract was let before 1945 was out. Although Convair were even then one of the world's largestaircraft companies they felt justifiably diffident about so great a stride into the unknown. It was a period in which severalcompletely new families of transonic wings were being discussed, without anyone having sufficient practical knowledge to recom-mend which type should be chosen. Back in the 1930s the N.A.C.A. had conducted a purely theoretical investigation intothe characteristics of wings of triangular plan-form. From the end of World War 2 crate-loads of captured German calculationsand tunnel data on transonic wing design became available, and a considerable proportion of the latter also suggested a triangular,or "delta", plan-form. The problem was placed in the hands of Convair's Downey plant, with prime responsibility assignedto Adclph Burstein, the assistant chief engineer of the San Diego Division, and Ralph H. Shick, chief of aerodynamic research.These experienced men tentatively decided to recommend a delta wing for the new fighter. Most of the German material on suchwings had stemmed from the Lippisch group. Convair tracked down Lippisch at Wright-Patterson A.F.B., and Shick flew thereto talk to the man himself. Shick came back to California convinced that the delta wasthe right choice, and his assurance injected a new spirit of enthusiasm and confidence within the company. Work wentahead during 1946 on what was then the only delta prograrrme in the world. For little over $150 a rough tunnel model wasmade, and the results were so impressive that the Air Force accepted the configuration for the future intercepter. Convairbuilt more, and better, models and launched a tunnel programme of previously unparallelled magnitude. Over 5,000 hours werelogged before an aeroplane was built. Finally the design and construction of a full-scale aeroplanebegan as the Model 7002, with Thomas M. Hemphill of San Diego as project engineer. Time and money were against himand he employed parts of five other aircraft in the design. In 1947 activities at the Downey Division were suspended and thework was transferred to the main plant at San Diego. Late in November of that year the first aircraft (U.S.A.F. serial number46-682) was mounted for tunnel testing at the N.A.C.A. Ames laboratory, and the subsequent results were described as "excep-tional". The Allison J33-A-23 engine was then installed and a long programme of ground testing and high-speed taxying beganat Muroc (now Edwards A.F.B.). The machine finally took to the air in the hands of E. D. ("Sam") Shannon, then San Diego chieftest pilot, just after dawn on September 18, 1948. As far as is known, this was the first flight of a true delta-wing aeroplane. Subsequent flight experience extended over several years, andthe 7002 was flown by many civilian and military pilots. By 1949 the original F-92 specification for a turbojet/rocket inter-cepter had been abandoned, but the 7002 was accepted by the Air Force as the XF-92A research vehicle. In 1951 it was back atEdwards for advanced U.S.A.F. testing; it was assigned to the N.A.C.A. the following year, and finally wound up as a U.S.A.F.travelling exhibit. It served to provide the U.S. Air Force and aircraft industrywith a vast quantity of data on delta-wing characteristics up to a Mach number of 0.95. Many designers consider that thedelta is ideally a supersonic configuration and, from the outset, Convair adopted a leading-edge sweep of 60 deg. and a lowthickness /chord ratio, thus making their test results applicable to the design of supersonic aircraft. They found that, althoughthe maximum lift coefficient was not high, and that it could be obtained only at very high angles of attack (a possible source oftrouble to the pilot), the wing otherwise performed admirably and seemed to offer the best overall basis upon which a supersonicintercepter design could be planned. One of the major variables concerned the choice of armament.By 1950, research by the U.S.A.F. had proved the feasibility of the collision-course attack, using folding-fin, spin-stabilized rockets;
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