Convair F-106 Delta Dart
The Convair F-106 Delta Dart is an all-weather interceptor aircraft designed and produced by the American aircraft manufacturer Convair.
The F-106 was designed in response to the 1954 interceptor program. Envisioned as an imagined "Ultimate Interceptor", it was a development of the F-102 Delta Dagger, and commenced as the F-102B prior to being redesignated by the United States Air Force. The F-106 was designed without a gun or provision for carrying bombs, instead carrying its AIM-4 Falcon air-to-air missiles within an internal weapons bay; its clean exterior was beneficial to supersonic flight. Major differences from the F-102 included the adoption of the more powerful Pratt & Whitney J75 turbojet engine, heavily redesigned air inlets along with a variable-geometry inlet duct to suit a wide range of supersonic speeds, and a general increase in size. On 26 December 1956, the first prototype performed its maiden flight. After flight testing demonstrated lesser performance gains than anticipated, the USAF only ordered 350 of the planned 1,000 F-106s.
Becoming operational in June 1959, the F-106 was the primary all-weather interceptor aircraft of the USAF through much of the Cold War era; it ended up being the final specialist interceptor to be used by the service to date. It was never used in combat nor were any exported. During the 1960s, a competitive evaluation between the F-106 and the McDonnell Douglas F-4 Phantom II determined the latter to be marginally superior, yet the type continued to be operated for a further two decades due to extensive demand for the F-4 in other roles. Convair proposed various improved models of the F-106, typically focused on the radar, communications, and other avionics, but none of these schemes were pursued. In one incident over Montana on 2 February 1970, an unmanned F-106 recovered from a flat spin after its pilot had ejected, belly landing relatively intact in a snow-covered field; it was recovered and continued to be flown for numerous years afterwards.
The F-106 was gradually withdrawn from USAF service during the 1980s as the arrival of newer air superiority fighters, particularly the McDonnell Douglas F-15 Eagle, had made the role of dedicated interceptors obsolete. Numerous F-106s were operated for a time by the Air National Guard. Many withdrawn aircraft were converted into target drones and redesignated QF-106 under the Pacer Six program, which were used up in 1998. A handful of F-106s were operated by NASA for experimental purposes, such as the Eclipse Project, until 1998.
Development
Background
The F-106 was the ultimate development of the USAF's 1954 interceptor program of the early 1950s. The initial winner of this competition had been the F-102 Delta Dagger, but early versions of this aircraft had demonstrated extremely poor performance, being limited to flying at subsonic speeds and relatively low altitudes. During the testing program the F-102 underwent numerous changes to improve its performance, notably the application of the area rule to the fuselage shaping and a change of engine, and the dropping of the advanced MX-1179 fire control system and its replacement with a slightly upgraded version of the MX-1 already in use on subsonic designs. The resulting aircraft became the F-102A, and in spite of being considered barely suitable for its mission, the Air Force sent out a production contract in March 1954, under which the first deliveries were expected during the following year.By December 1951, the Air Force had already turned its attention to a further improved version, which was initially referred to as the F-102B. The main planned change was the replacement of the F-102A's Pratt & Whitney J57 with the more powerful Wright J67. By the time this engine would be available, the MX-1179 was expected to be available, and thus it was selected as well. The intended result would be the "ultimate interceptor" that the USAF had originally sought. However, while initial work on the Olympus design appeared to go well, by August 1953 Wright was already a full year behind schedule in development. Continued development did not resolve problems with the engine, and in early 1955 the Air Force approved the switch to the Pratt & Whitney J75.
The J75 turbojet engine was a bigger engine than the J57 in the F-102A and it needed greater airflow in the engine. This demanded changes to the air inlets of the engine to allow more airflow and led to the further refinement of using a somewhat shorter variable-geometry inlet duct to allow the intakes to be tuned to best performance across a wide range of supersonic speeds. The fuselage grew slightly longer, and was cleaned up and simplified in many ways. The wing was slightly enlarged in area, and a redesigned vertical tail surface was used. The engine's two-position afterburner exhaust nozzle was also used for idle thrust control, held open to decrease thrust by 40%, resulting in slower taxiing and less brake wear.
Competing efforts and production arrangements
Throughout its early development, the F-102B had to compete for attention and resources with the F-102A; the aviation author Marcelle Knaack observed that there were fewer funds to develop the more capable systems of the F-102B, which would have been useful in more quickly overcoming some of the technical difficulties that arose. The number of F-102As on order grew substantially beyond that which had been originally forecast, indicative of the growing importance attached to what had once been intended to be an interim or 'stop-gap' aircraft to fill in until the F-102B could be delivered. During December 1955, a mock-up with the expected layout of the MX-1179, now known as the MA-1, was inspected and approved.On 18 April 1956, an extended production contract for 17 F-102Bs was issued to Convair, representing substantially fewer aircraft than had been originally anticipated at this stage. On 17 June of that year, the aircraft was officially re-designated as the F-106A. On 18 August 1956, the USAF issued a systems development directive that called for development and production of the F-106 Knaack attributed this policy as being responsible for several later problems in the program. During April 1957, the USAF formally rejected Convair's F-102C proposal to concentrate on the more advanced F-106 program, which it had then anticipated to enter service during the following year.
Flight testing
On 26 December 1956, the first prototype F-106, an aerodynamic test bed, performed its maiden flight from Edwards Air Force Base. On 26 February 1957, the second prototype, which was outfitted with a fuller set of equipment, made its first flight. Early flight testing around the end of 1956 and beginning of 1957 demonstrated somewhat disappointing results, having achieved less of a performance gain over the F-102 than had been anticipated. Specifically, both the acceleration and maximum speed were beneath Convair's own estimates. Furthermore, both the engine and avionics proved to be somewhat unreliable. These combined problems, and the delays associated with them, were nearly responsible for the termination of the program.However, the service decided to persist with the F-106 program after the Air Defense Command had heavily advocated for it. Based upon the test data submitted, USAF officials had determined that modifications to the inlet duct cowling and charging ejectors were likely to increase both acceleration and speed; modifications would be made following the completion of Category II testing and were evaluated during Category III testing. At this stage, the service enacted several measures to hasten development towards production; in April 1957, it authorized the conditional acceptance of several F-106s being used by Convair for flight testing; it also took several quick decisions to settle outstanding development questions. By mid-1957, funding for 120 F-106As had been allocated. The USAF ultimately opted to order 350 F-106s, substantially fewer than the planned fleet of 1,000 aircraft. Deliveries of the single-seat F-106A and the twin-seat F-106B combat-capable trainer variant commenced to 15 fighter interceptor squadrons in October 1959.
World speed record
On 15 December 1959, Major Joseph W. Rogers set a world speed record of 1,525.96 mph in a Delta Dart at 40,500 ft. That year, Charles E. Myers flew the same model aircraft at 1,544 mph.Design
The F-106 was envisaged as a specialized all-weather missile-armed interceptor to shoot down bombers. It was complemented by other Century Series fighters for other roles such as daylight air superiority or fighter-bombing. To support its role, the F-106 was equipped with the Hughes MA-1 integrated fire-control system, which could be linked to the Semi-Automatic Ground Environment network for ground control interception missions, allowing the aircraft to be steered by controllers. The MA-1 proved extremely troublesome and was eventually upgraded more than 60 times in service.Similarly to the F-102, the F-106 was designed without a gun, or provision for carrying bombs, but it carried its missiles in an internal weapons bay for clean supersonic flight. It was armed with four Hughes AIM-4 Falcon air-to-air missiles -guided, along with a single 1.5 kiloton-warhead AIR-2 Genie unguided air-to-air rocket intended to be fired into enemy bomber formations. Like its predecessor, the F-102 Delta Dagger, it could carry a drop tank under each wing. Later fighters such as the McDonnell Douglas F-4 Phantom II and McDonnell Douglas F-15 Eagle carried missiles recessed in the fuselage or externally, but stealth aircraft would re-adopt the idea of carrying missiles or bombs internally for reduced radar signature.
The first ejection seat fitted to early F-106s was a variation of the seat used by the F-102 and was called the Weber interim seat. It was a catapult seat which used an explosive charge to propel it clear of the aircraft. This seat was not a zero-zero seat and was inadequate for ejections at supersonic speeds as well as ground level ejections and ejections at speeds below and. The second seat that replaced the Weber interim seat was the Convair/ICESC Supersonic Rotational B-seat, called the supersonic "bobsled", hence the B designation. It was designed with supersonic ejection as the primary criterion since the F-106 was capable of Mach-2 performance. Fighter pilots viewed high speed ejections as the most important. Seat designers viewed an ejection at low altitude and slow speed as the most likely possibility. The ejection sequence with the B-seat was quite complicated and there were some unsuccessful ejections that resulted in pilot fatalities. The third seat, that replaced the Convair B-seat, was the Weber Zero-Zero ROCAT seat. Weber Aircraft Corporation designed a "zero-zero" seat to operate at up to. High-altitude supersonic ejections were rare and ejections at relatively low altitudes and low speeds were more likely. The Weber "zero-zero" seat was satisfactory and was retrofitted to the F-106 after 1965.