Convair F-102 Delta Dagger
The Convair F-102 Delta Dagger is an interceptor aircraft designed and produced by the American aircraft manufacturer Convair. A member of the Century Series, the F-102 was the first operational supersonic interceptor and delta-wing fighter operated by the United States Air Force.
The F-102 was designed in response to a requirement, known as the 1954 Ultimate Interceptor, produced by USAF officials during the late 1940s. Its main purpose was to be the backbone of American air defences and to intercept approaching Soviet strategic bomber fleets during the Cold War. The aircraft was designed alongside a sophisticated fire-control system ; however, a simplified unit had to be adopted due to development difficulties. It used an internal weapons bay to carry both guided missiles and rockets. On 23 October 1953, the prototype YF-102 performed its maiden flight; however, it was destroyed in an accident only nine days later. The second prototype allowed flight testing to resume three months later, but results were disappointing: as originally designed, the aircraft could not achieve Mach 1 supersonic flight.
To improve its performance prior to quantity production commencing, the F-102 was redesigned, its fuselage was reshaped in accordance with the area rule while a thinner and wider wing was also adopted. Flight testing demonstrated sufficient performance improvements for the USAF to be persuaded to permit its production; a new production contract was signed during March 1954. Following its entry to USAF service in 1956, the F-102 promptly replaced various subsonic fighter types, such as the Northrop F-89 Scorpion, in the interceptor role. The F-102C tactical attack model, equipped with several improvements, including a more powerful engine and Gatling gun, was proposed but not ultimately pursued. A total of 1,000 F-102s were built, both for the USAF and a handful of export customers, including the Hellenic Air Force and the Turkish Air Force.
By the 1960s, USAF F-102s had participated in a limited capacity in the Vietnam War as a bomber escort and even in the ground-attack role. The aircraft was supplemented by McDonnell F-101 Voodoos and, later on, by McDonnell Douglas F-4 Phantom IIs. Over time, many F-102s were retrofitted with infrared search/tracking systems, radar warning receivers, transponders, backup artificial horizons, and modified fire-control systems. Throughout the mid-to-late 1960s, many USAF F-102s were transferred from the active duty Air Force to the Air National Guard, and, with the exception of those examples converted to unmanned QF-102 Full Scale Aerial Target drones, the type was totally retired from operational service in 1976. Its principal successor in the interceptor role was the Mach 2-capable Convair F-106 Delta Dart, which was an extensive redesign of the F-102.
Design and development
Background
On 8 October 1948, the board of senior officers of the United States Air Force issued recommendations that the service organize a competition for a new interceptor scheduled to enter service in 1954; as such, the all-new design would initially be dubbed the "1954 Ultimate Interceptor". Four months later, on 4 February 1949, the USAF approved the recommendation and prepared to hold a corresponding competition during the following year. In November 1949, the USAF decided that the new aircraft would be built around a fire-control system. The FCS was to be designed before the airframe to ensure compatibility. The airframe and FCS together were called the weapon system.In January 1950, the USAF's Air Materiel Command issued request for proposals to 50 companies for the FCS, of which 18 responded. By May, the list was revised downward to 10. Meanwhile, a board at the U.S. Department of Defense headed by Major General Gordon P. Saville reviewed the proposals, and distributed some to the George E. Valley-led Air Defense Engineering Committee. Following recommendations by the committee to the Saville Board, the proposals were further reduced to two competitors, Hughes Aircraft and North American Aviation. Although the Valley Committee thought it was best to award the contract to both companies, Hughes was chosen by Saville and his team on 2 October 1950.
In June 1950, the requirement for the airframe was formally issued; during January 1951, six aircraft manufacturers submitted nine responses. On 2 July 1954, three of the responding companies, Convair, Republic, and Lockheed, were authorised to proceed with the building of a mockup. Upon completion, the three designs would be competitively reviewed, the best of which would lead to the awarding of a single production contract under the name Project MX-1554. Prior to this requirement, Convair had performed considerable early research into delta-winged aircraft and had experimented with various different designs, two of which fell under the name P-92. For the era, Convair's submitted design was relatively unorthodox, not only in terms of the delta wing configuration but the decision to carry all munitions within an internal weapons bay to reduce drag; despite this, Republic's design was even more radical, proposing to use ramjet propulsion to attain speeds in excess of Mach 3.
Selection
Ultimately, Convair's design emerged as the front runner for the requirement, which was officially designated XF-102. Lockheed had chosen to drop out to concentrate on other opportunities while Republic's design had been judged to involve too much technical risk to meet the 1954 deadline for service entry, thus was disqualified, making Convair the de facto winner. The development of three different designs has been considered to be too expensive to proceed with, thus only Convair was permitted to do so in November 1951. From an early stage, USAF officials had decided to use the Cook-Craigie Plan for the aircraft's manufacturing; under this concept, production tooling and facilities would be created while a small pre-production batch of aircraft would be completed, the aim being to eliminate the need for a lengthy prototype program, instead incorporating any changes required into the production line. However, if substantial modifications were necessary, re-tooling would then become necessary as well. In December 1951, in order to accelerate the aircraft's development, it was proposed to equip the prototypes and pre-production aircraft with the less-powerful Westinghouse J40 turbojet.During early 1953, by which point construction of the first aircraft had reached an advanced stage, it had become clear that there were serious design challenges present, including wind tunnel testing that revealed early performance projections to have been overly optimistic. Furthermore, there had been sustained delays to both the Curtiss-Wright J67 engine, a licensed derivative of the Bristol-Siddeley Olympus which was still in development, and the MA-1 FCS; to address the latter, decision makers opted to order an interim aircraft with the J40 and a simpler FCS into production as the F-102A. The failure of the J40 led to the Pratt & Whitney J57 turbojet with afterburner, rated with of thrust, being substituted for the prototypes and F-102As. This aircraft was intended to be temporary, pending the development of the more advanced F-102B, which would employ the more advanced J67. The F-102B would later evolve to become the F-106A, dubbed the "Ultimate Interceptor".
On 23 October 1953, the YF-102 prototype conducted its first flight from Edwards Air Force Base, piloted by Convair's chief test pilot Richard L. Johnson. Its flying career was very brief as it was lost in an accident only nine days later during a failed attempt to reach Mach 1. The accident, which was caused by severe buffeting, seriously injured Johnson. The second aircraft flew on 11 January 1954, confirming a dismal performance. Transonic drag was much higher than expected, and the aircraft was limited to Mach 0.98, with a ceiling of, far below the requirements.
Major redesign
During mid 1953, Convair concluded that it needed to take action to address the F-102's shortcomings to prevent its cancellation, and promptly embarked on a major redesign effort. It was decided to incorporate the recently discovered area rule, the application of which simultaneously simplified both production and maintenance of the aircraft. This redesign entailed the lengthening of the fuselage by, being "pinched" at the midsection, with two large fairings on either side of the engine nozzle, with revised intakes and a new, narrower canopy. A more powerful model of the J57 was installed while the aircraft structure was also lightened.In parallel to this effort, the wing was also redesigned to be both thinner and wider. The leading edge was reprofiled with a conical droop, with the apex at the root, as to improve handling at low speeds. Because the droop remained within the shock cone of the leading edge, the drag rise at supersonic speeds was minimal. A second, inboard fence was also added at the time. A new canopy was also adopted while the tail was shifted slightly aft. The level of changes that could be implemented were restrained by the redesign having occurred at such an advanced stage of development. Yet, the overall changes made were so substantial that two-thirds of the roughly 30,000 tools created to manufacture the YF-102 were scrapped or modified before quantity production had even commenced.
On 20 December 1954, the first revised aircraft, designated YF-102A, made its first flight only 118 days after work on the redesign had started. The next day, it exceeded Mach 1 for the first time. The revised design quickly demonstrated that it could attain a speed of Mach 1.22 and a ceiling of. These performance improvements were sufficient for the USAF to agree to procure the F-102; accordingly, a new production contract was signed during March 1954. On 24 June 1955, the first flight of a production standard F-102 occurred. From the 26th production aircraft onwards, a taller vertical tail with a 40 percent greater surface area was fitted to counteract flutter and a lack of directional control at high speeds; existing aircraft were also retrofitted with this change.