The Convair F-106 Delta Dart was an all-weather interceptor aircraft designed and produced by the American aircraft manufacturer Convair.

The F-106 was designed as the so-called "Ultimate Interceptor" as a consequence of the 1954 interceptor program of the early 1950s. It was a development of the F-102 Delta Dagger, and thus was originally designed as the F-102B prior to being redesignated by the United States Air Force (USAF). 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, application of the area rule to the fuselage shaping, and a general increase in size. On 26 December 1956, the first prototype performed its maiden flight. After flight testing demonstrated less performance gains than anticipated, the USAF ultimately 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 export opportunities secured. 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 on account of 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 would be pursued by the service. In one high-profile incident over Montana on 2 February 1970, an unmanned F-106 recovered from a flat spin after its pilot had ejected, 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The F-106 was gradually withdrawn from USAF service during the 1980s as the arrival of newer air superiority fighters, particularly the McDonnell Douglas F-15 Eagle, had made the role of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 increasingly redundant. Numerous F-106s would be operated for a time by the Air National Guard. Many withdrawn aircraft were promptly converted into target drones and redesignated QF-106 under the Pacer Six program; in this guise, the aircraft continued being used up until 1998.[1][2][3] A handful of F-106s were operated by NASA for experimental purposes, such as the Eclipse Project, through to 1998.

Development

Background

The F-106 was the ultimate development of the USAF's 1954 interceptor program of the early 1950s.[4] 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.[5] 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.[6][7]

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 (which had itself replaced the original J40[8]) with the more powerful Bristol Olympus, which was produced under license as the Wright J67.[9] By the time this engine would be available, the MX-1179 was expected to be available, and thus it was selected as well. The result would be the "ultimate interceptor" that the USAF had wanted originally.[10] However, while initial work on the Olympus 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.[11][12][N 1]

The J75 was somewhat larger than the J57 in the F-102A, and had greater mass flow. This demanded changes to the inlets to allow more airflow, and this led to the further refinement of using a variable-geometry inlet duct to allow the intakes to be tuned to best performance across a wide range of supersonic speeds. This change also led to the ducts being somewhat shorter. 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. The nozzle was held open reducing idle thrust by 40% giving slower taxiing and less brake wear.[13]

Competing efforts and production arrangements

Throughout the early development of the F-102B, it had to compete for attention and resources with the F-102A; the aviation author Marcelle Knaack observed that there were less 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 would be encountered.[12] The number of F-102As on order grew substantially beyond that which 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.[14]

On 18 April 1956, in a clear sign of growing confidence that the aircraft was improving, an extended production contract for 17 F-102Bs was issued to Convair; however, this order was for substantially less aircraft than had been originally anticipated at this stage.[14] On 17 June of that year, the aircraft was officially re-designated as the F-106A.[15][16][17] On 18 August 1956, the USAF issued a systems development directive that called for development and production of the F-106 to occur simultaneously; Knaack attributed this policy as being responsible for several later problems in the programme.[18] During April 1957, the USAF formally rejected Convair's F-102C proposal (essentially a reengined model of the F-102) to concentrate on the more advanced F-106 program, which it had then anticipated to enter service during the following year.[19]

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.[20][18] 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.[21] Furthermore, both the engine and avionics proved to be somewhat unreliable.[22] These combined problems, and the delays associated with them, were nearly responsible for the termination of the programme.[20][23]

However, the service decided to persist with the F-106 programme after the Air Defense Command had heavily advocated for it.[24] 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.[21] 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.[25] By mid-1957, funding for 120 F-106As had been allocated.[26] The USAF ultimately opted to order 350 F-106s, substantially less than the planned 1,000 fleet of 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.[27][26]

World Speed record

F-106A Delta Darts from 5 FIS at CFB Moose Jaw in 1982

On 15 December 1959, Major Joseph W. Rogers set a world speed record of 1,525.96 mph (2,455.79 km/h) in a Delta Dart at 40,500 ft (12,300 m).[28][29][30] That year, Charles E. Myers flew the same model aircraft at 1,544 mph (2,484 km/h).[31]

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.[26] 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 (SAGE) network for ground control interception (GCI) 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.[32][33]

Similar 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 (either AIM-4F/G infra-red guided missiles or semi-active radar homing (SARH)-guided (which detected reflected radar signals) AIM-4E missiles[34]), along with a single 1.5 kiloton-warhead AIR-2 (MB-2) Genie unguided air-to-air rocket intended to be fired into enemy bomber formations.[35] Like its predecessor, the F-102 Delta Dagger, it could carry a drop tank under each wing.[36] 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 120 knots (140 miles per hour; 220 kilometres per hour) and 2,000 feet (610 metres). The second seat that replaced the Weber interim seat was the Convair/ICESC (Industry Crew Escape System Committee) Supersonic Rotational B-seat, called the supersonic "bobsled", hence the B designation.[37][38] 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 (for Rocket Catapult) seat. Weber Aircraft Corporation designed a "zero-zero" seat to operate at up to 600 knots (690 miles per hour; 1,100 kilometres per hour). 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.[39]

Operational history

A Soviet Tu-95 is intercepted by a F-106A off Cape Cod in 1982

Early operations of the F-106 were troubled by numerous technical issues, these included generator defects, fuel-flow issues (particularly during cold weather), and combustor-starter malfunctions.[40] During December 1959, all F-106s were temporarily grounded following the accidental jettisoning of the canopy mid-flight on one aircraft. Many, but not all, of these problems were resolved by the start of 1961; this can be partially attributed to two major modification and retrofit programmes conducted during this timeframe.[41] Following the resolution of initial teething problems – in particular an ejection seat that killed the first 12 pilots to eject from the aircraft[42] – its exceptional performance led to the aircraft becoming relatively popular amongst its pilots.

The F-106 served in the contiguous US, Alaska, and Iceland, as well as for brief periods in Germany and South Korea.[43] The F-106 was the second highest sequentially numbered P/F- aircraft to enter service under the old number sequence (the F-111 was highest), before the system was reset under the 1962 United States Tri-Service aircraft designation system. In service, the F-106's official name, "Delta Dart," was rarely used, and the aircraft was universally known simply as "The Six."[44] The arrival of the F-106 in quantity quickly led to the withdrawal of various older aircraft that were being used in the interceptor role, such as the North American F-86 Sabre and the Northrop F-89 Scorpion.[45]

Although contemplated for use in the Vietnam War, the F-106 never saw combat, nor was it exported to foreign users. After the cancellation of their own Avro Arrow, the Canadian government briefly considered purchasing the F-106C/D.

To standardize aircraft types, the USAF was directed to conduct Operation Highspeed, a flyoff competition between the USAF F-106A and the U.S. Navy F4H-1 (F-4B) Phantom, which was not only as capable as the F-106 as a missile-armed interceptor but could carry as large a bomb load as the Republic F-105 Thunderchief fighter-bomber.[46] The Phantom was the winner but would first be used to escort and later replace the F-105 fighter-bomber in the late 1960s before replacing older interceptors in Air Defense Command in the 1970s.

An F-106A of the 87th FIS above Charleston AFB, SC in 1982.

The F-106 was progressively updated in service, with improved avionics, a modified wing featuring a noticeable conical camber, an infrared search and track system, streamlined supersonic wing tanks which provided virtually no degradation to overall aircraft performance, better instrumentation and features like an inflight refuelling receptacle and an arrestor hook for landing emergencies.[47][33]

Air-to-air combat testing suggested "The Six" was a reasonable match for the F-4 Phantom II in a dogfight, with superior high-altitude turn performance and overall maneuverability (aided by the aircraft's lower wing loading). The Phantom had better radar – operated by an additional crewman – and could carry a load of up to four radar-guided AIM-7 Sparrow and four infrared AIM-9 Sidewinder missiles, while the AIM-4 Falcon missiles carried by the F-106 proved a disappointment for dogfighting over Vietnam.[48] The F-4 had a higher thrust/weight ratio with superior climb, better high speed/low-altitude maneuverability and could be used as a fighter-bomber. Air combat experience over Vietnam showed the need for increased pilot visibility and the utility of a built-in gun, which had been added to the "E" variant of USAF Phantoms.

A NASA QF-106 Delta Dart from the Eclipse program shows its area ruled fuselage

In 1972, some F-106As were upgraded in Project Six Shooter that involved fitting the F-106 with a new canopy without metal bracing which greatly improved pilot visibility.[49] Also added was an optical gunsight and provision for a M61 Vulcan 20 mm cannon. The M61 Vulcan had 650 rounds of ammunition in the center weapons bay and it replaced the AIM-26 Super Falcon or Genie. The F-15A Eagle started replacing the F-106 in 1981, with "The Sixes" typically passed on to Air National Guard units. The F-106 remained in service in various USAF and ANG units until 1988.[1]

Retirement and conversion into drones

Between 1 June 1983 and 1 August 1988 the Delta Darts were incrementally retired and sent to the Military Storage and Disposition Center in Arizona.[50][51] When the need for a high performance Full Scaled Aerial Target Drone was required, the USAF began withdrawing Delta Darts from storage. Starting in 1986, 194 of the surviving surplus aircraft were converted into target drones and these were designated QF-106As and used for target practice vehicles under the Pacer Six Program by the Aerial Targets Squadron.[52] The last was destroyed in January 1998.[2][3] The drones were still capable of being flown as manned aircraft, such as for ferrying to a test; during the test they were flown unmanned.[53] The QF-106 replaced the QF-100 Super Sabre drone; the last shoot down of a QF-106 (57-2524) took place at Holloman AFB on 20 February 1997 after which the QF-106 was superseded by the QF-4S and QF-4E Phantom II drone.

NASA research and test aircraft

Six F-106s were retained by NASA for test purposes through 1998. An F-106B two-seat trainer was operated by NASA Langley Research Center between 1979 and 1991.[54] This Delta Dart was used in research programs ranging from testing supersonic engines to improving maneuverability of fighters. Between 1980 and 1986 the aircraft was modified for the purpose of lightning strike research and became known as the Lightning Strike Plane and was struck 714 times without damage.[55][56] On one hour-long flight at 38,000 feet (12,000 metres) in 1984, lightning struck the research aircraft 72 times.[57] One significant modification was the replacement of the composite nose radome by a metallic radome. Although the maximum speed of the F-106 was Mach 2.3, during the lightning experiments it was flown at subsonic speeds into clouds at 300 knots (350 miles per hour; 560 kilometres per hour) from 5,000 to 40,000 feet (1,500 to 12,200 metres).[58] The aircraft was equipped with optical sensors which consisted of a video camera and a light detector. Data acquisition was performed with 1980s state of the art digital waveform recorders.

Eclipse project

NASA used six drones in its Eclipse Project which ran from 1997 to 1998.[59][60] The Dryden Flight Research Center supported project Eclipse which sought to demonstrate the feasibility of a reusable Aerotow-launch vehicle. The objective was to tow, inflight, a modified QF-106 aircraft with a C-141A transport aircraft. The test demonstrated the possibility of towing and launching a space launch vehicle from behind a tow plane.[61][62]

The Cornfield Bomber

The Cornfield Bomber, pictured here shortly after earning its nickname.

Main article: Cornfield Bomber

On 2 February 1970, an F-106 of the 71st Fighter-Interceptor Squadron, piloted by Captain Gary Foust, entered a flat spin over Montana. Foust followed procedures and ejected from the aircraft. The resulting change of balance caused the aircraft to stabilize and later land "wheels up" in a snow-covered field, suffering only minor damage. The aircraft, promptly nicknamed "The Cornfield Bomber", was then sent back to base by rail, repaired and returned to service, and is now on display at the National Museum of the United States Air Force.[63]

The Kawanishi H8K[a] was a flying boat used by the Imperial Japanese Navy Air Service during World War II for maritime patrol duties. The Allied reporting name for the type was "Emily".

The Kawanishi H8K was a large, four-engine aircraft designed for long range and extended endurance on patrols or bombing missions typically flown alone over the ocean. The prototype first flew in January 1941, and H8K1s made their first combat sortie in March 1942. The robust H8K2 "Emily" flying boat was also fitted with powerful defensive armament, for which Allied pilots had substantial respect wherever this aircraft was encountered in the Pacific theater. Aircraft historian René Francillon called the H8K "the most outstanding water-based combat aircraft of the Second World War."[1]

The LTV A-7 Corsair II is an American carrier-capable subsonic light attack aircraft designed and manufactured by Ling-Temco-Vought (LTV).

The A-7 was developed during the early 1960s as replacement for the Douglas A-4 Skyhawk. Its design was derived from the Vought F-8 Crusader; in comparison with the F-8, the A-7 is both smaller and restricted to subsonic speeds, its airframe being simpler and cheaper to produce. Following a competitive bid by Vought in response to the United States Navy's (USN) VAL (Heavier-than-air, Attack, Light) requirement, an initial contract for the type was issued on 8 February 1964. Development was rapid, first flying on 26 September 1965 and entering squadron service with the USN on 1 February 1967; by the end of that year, A-7s were being deployed overseas for the Vietnam War.

Initially adopted by USN, the A-7 proved attractive to other services, soon being adopted by the United States Air Force (USAF) and the Air National Guard (ANG) to replace their aging Douglas A-1 Skyraider and North American F-100 Super Sabre fleets. Improved models of the A-7 would be developed, typically adopting more powerful engines and increasingly capable avionics. American A-7s would be used in various major conflicts, including the Invasion of Grenada, Operation El Dorado Canyon, and the Gulf War. The type was also used to support the development of the Lockheed F-117 Nighthawk.

The A-7 was also exported to Greece in the 1970s and to Portugal in the late 1980s. The USAF and USN opted to retire their remaining examples of the type in 1991, followed by the ANG in 1993 and the Portuguese Air Force in 1999. The A-7 was largely replaced by newer generation fighters such as the General Dynamics F-16 Fighting Falcon and the McDonnell Douglas F/A-18 Hornet. The final operator, the Hellenic Air Force, withdrew the last A-7s during 2014.