General Dynamics F-111K

The General Dynamics F-111K was a planned variant of the General Dynamics F-111 Aardvark medium-range interdictor and tactical strike aircraft by General Dynamics, to meet a requirement for such an aircraft for the Royal Air Force.The project was initiated in 1965 following the cancellation of the BAC TSR-2 strike aircraft. The aircraft was planned as a hybrid of several variants of the F-111 as a way of producing an aircraft for the specific needs of the United Kingdom. A RAF order for 50 aircraft, made in 1967, was cancelled a year later.

In the early 1960s, the British Aircraft Corporation was in the process of developing a new strike aircraft for the Royal Air Force to replace the English Electric Canberra. This aircraft, designated as "TSR-2" (Tactical Strike and Reconnaissance), had a large set of requirements listed by the government, and had led to TSR-2 becoming a hugely complex machine; it was intended that it be able to undertake both conventional and nuclear strike missions at high and low level, in all weathers, at supersonic speeds. As a consequence, the costs of the project began to increase, leading to it becoming the most expensive aviation project in British history, at a time when defence spending was being cut. This led to the RAF being asked to look for potential alternatives to TSR-2, in the event of it being cancelled.At the same time, the Australian government was looking for a replacement for the Canberras operated by the Royal Australian Air Force (RAAF), and was investigating a number of options, including the TSR-2 and the General Dynamics F-111 then being developed for the US TFX Program. The versatility of the F-111 and uncertainty over the TSR-2 led, in 1963, to contracts for the RAAF-specific General Dynamics F-111C.An incoming Labour government expressed its support for the TSR-2, although the RAF was asked to also evaluate the F-111 as a cheaper option. In April 1965, the TSR-2 was officially cancelled and the RAF again looked at the possibility of acquiring up to 110 F-111s.

No firm commitment was made to the F-111 until the publication of the 1966 Defence White Paper, although it was the government's preferred option. Following the publication of the defence review, it was announced that up to 50 F-111s would be procured for the RAF; like the Australian version, these would be highly adapted to suit the unique set of British requirements. The intention was to form an initial four operational squadrons, plus an Operational Conversion Unit, with two stationed in the UK and two forming part of the UK's forces East of Suez. The intention was that long-range, land based F-111s would be used to replace the strike capability of the CVA-01 aircraft carriers that were cancelled in the White Paper. Although there was no public announcement as to specific squadrons that would receive the F-111, a document from early 1966 by the AOC-in-C of Bomber Command, Air Chief Marshal Sir Wallace Kyle, indicated that 12 Squadron (then a Vulcan squadron assigned to the strategic nuclear role), together with the inactive 7 (previously Valiant), 15 (Victor) and 40 (Canberra) Squadrons, would receive the aircraft upon their delivery.In April 1966, a firm order was placed for 10 F-111s for the RAF, with options for another 40, covering the standard F-111K models and a number of dual-control TF-111K trainers, with the purchase price set around £2.1m ($5.95m) per unit (1965 prices). This was intended to show a significant reduction in cost when compared with the development and estimated production costs of TSR-2. At the same time, a pair of Victor squadrons had been moved out of RAF Honington, which was earmarked for conversion to accommodate the F-111 force. However, at the same time the actual cost of F-111 production had increased; in April 1967, when the RAF's 40 additional aircraft were ordered, the per unit cost of the F-111C for the RAAF was US$9m. This eventually led to an admission from the British government that the cost would increase from the initial figure set out – in 1967, the then Secretary of State for Defence, Denis Healey, stated that adjusting for inflation was taken into account, which would add approximately 2.5% to the cost of each aircraft. This did not include the cost of installing the British adaptations. The total estimate cost by the time the last aircraft was due to be delivered in 1970 was approximately £2.7m. Despite this, the government still maintained that the F-111 programme (combined with the proposed AFVG aircraft) would be cheaper than TSR-2 to the tune of approximately £700m.

The first two aircraft began assembly in July 1967, and were issued with the serial numbers XV884 and XV885. These were intended as development aircraft, to undertake airframe, avionics and weapons testing prior to them being refurbished as operational units. At the same time, the remainder of the planned 50 strong fleet were allocated serials from XV886-887 (TF-111K) and XV902-947 (F-111K). The first two airframes were in the final stages of assembly at General Dynamics' plant at Fort Worth, Texas in early 1968 when the Government then issued a new policy that would see the majority of British forces stationed East of Suez withdrawn by 1971. At the same time it also decided to cancel the F-111K procurement. The devaluation of sterling in 1967 had led to the per unit cost rising to approximately £3m. Additionally, the production schedules were slipping; while the RAAF had its first F-111 delivered in 1968, official acceptance of the type into service did not occur until 1973 due to structural and development problems (which led to the RAAF having to lease 24 F-4 Phantoms as an interim measure). All of the components that had been assembled for the production of the main F-111K fleet that shared commonality were diverted to the FB-111A program, while the two aircraft under construction were re-designated as YF-111As with the intention that they be used as test aircraft in the F-111A program. Ultimately however, the two F-111Ks were never operated as test aircraft – in July 1968, almost exactly a year after the first airframe began construction, the US Air Force decided not to take them over, and General Dynamics were ordered to use them for component recovery.

The cancellation of the F-111K still left a requirement for a strike aircraft to replace the Canberra, so the government ordered 26 new Blackburn Buccaneer aircraft for the RAF to operate alongside ex-Fleet Air Arm Buccaneers that were being moved to the RAF following the phased withdrawal of fixed wing carrier aviation in the Royal Navy – this was despite the Buccaneer having been rejected as a contender for the original RAF requirement that had led first to the selection and cancellation of TSR-2, and subsequently the F-111K. No. 12 Squadron, one of the units that had been proposed to operate the F-111, became operational as the first RAF Buccaneer squadron at RAF Honington in 1969. With responsibility for the UK's nuclear deterrent passing to the Royal Navy in 1969, Vulcans were transferred from the strategic bomber role to the long range air interdiction role that would have been fulfilled by the F-111.The ending of the F-111 procurement, combined with the cancellation of the AFVG project, led to Britain eventually joining the multi-national working group to develop the "Multi-Role Combat Aircraft" in 1968; this led to the formation of Panavia and the ultimate development of the Tornado, an aircraft that assumed the roles of low-level strike and long range interdiction planned for the F-111.

The F-111K was to be based around the airframe of the original F-111A version built for the U.S. Air Force, but was to feature a number of alterations and adaptations. Structurally, the aircraft would be similar to F-111A with the heavy duty undercarriage from the strategic bomber version. This allowed for a greater gross weight to be designed into the aircraft. The other major design change from the F-111A was in its avionics, with the design calling for the Mark II package developed for the F-111D version, which featured a new inertial navigation and attack system, incorporating the Rockwell International AN/APQ-130 attack radar, an IBM on-board computer, the Marconi AN/APN-189 doppler navigation radar and the Sperry Corporation AN/APQ-128 terrain following radar. The plan was then to pair this avionics package with British designed and developed mission systems, of which the main elements were the reconnaissance capability and weapon carriage. The F-111K was to feature a revised weapons bay, containing a new removable centreline weapons pylon, which was beneficial given the design of the underwing pylons – the F-111 had four stations under each wing, but only the inner pair were designed to pivot, meaning that the outer pair could not be used with the wings in full sweepback mode. All of the weapon pylons featured British designed ejector rack units. The aircraft was given provision for a pallet inside the weapons bay that would feature a British designed reconnaissance system, with three camera windows located next to the nosewheel undercarriage (which the US versions were not fitted with). The aircraft was designed with an aerial refuelling probe compatible with the "probe and drogue" system used by the RAF, similar to the one fitted to the F-111B, although mounted differently.

The Air Force and Navy requirements appeared to be different. However, on 14 February 1961, the new U.S. Secretary of Defense, Robert McNamara, formally directed that the services study the development of a single aircraft that would satisfy both requirements. Early studies indicated the best option was to base the Tactical Fighter Experimental (TFX) on the Air Force requirement and a modified version for the Navy. In June 1961, Secretary McNamara ordered the go ahead on TFX despite Air Force and the Navy efforts to keep their programs separate.The USAF and the Navy could only agree on swing-wing, two seat, twin engine design features. The USAF wanted a tandem seat aircraft for low level penetration, while the Navy wanted a shorter, high altitude interceptor with side by side seating. Also, the USAF wanted the aircraft designed for 7.33 g with Mach 2.5 speed at altitude and Mach 1.2 speed at low level with a length of approximately 70 ft (21 m). The Navy had less strenuous requirements of 6 g with Mach 2 speed at altitude and high subsonic speed (approx. Mach 0.9) at low level with a length of 56 ft (17.1 m). The Navy also wanted a 48-inch (120 cm) radar dish for long range and a maximum takeoff weight of 50,000 pounds (23,000 kg). So McNamara developed a basic set of requirements for TFX based largely on the Air Force's requirements. He changed to a 36-inch (91 cm) dish for compatibility and increased the maximum weight to approximately 60,000 lb (27,200 kg) for the Air Force version and 55,000 lb (24,900 kg) for the Navy version. Then on 1 September 1961 he ordered the USAF to develop it. A request for proposal (RFP) for the TFX was provided to industry in October 1961. In December of that year Boeing, General Dynamics, Lockheed, McDonnell, North American and Republic submitted their proposals. The proposal evaluation group found all the proposals lacking, but the best should be improved with study contracts. Boeing and General Dynamics were selected to enhance their designs. Three rounds of updates to the proposals were conducted with Boeing being picked by the selection board. Instead Secretary McNamara selected General Dynamics' proposal in November 1962 due to its greater commonality between Air Force and Navy TFX versions. The Boeing aircraft versions shared less than half of the major structural components. General Dynamics signed the TFX contract in December 1962. A Congressional investigation followed, but did not change the selection.

The Air Force F-111A and Navy F-111B variants used the same airframe structural components and TF30-P-1 turbofan engines. They featured side by side crew seating in an escape capsule as required by the Navy, versus individual ejection seats. The F-111B's nose was 8.5 feet (2.59 m) shorter due to its need to fit on existing carrier elevator decks, and had 3.5 feet (1.07 m) longer wingspan to improve on-station endurance time. The Navy version would carry an AN/AWG-9 Pulse-Doppler radar and six AIM-54 Phoenix missiles. The Air Force version would carry the AN/APQ-113 attack radar and the AN/APQ-110 terrain-following radar and air-to-ground ordnance. Lacking experience with carrier-based fighters, General Dynamics teamed with Grumman for assembly and test of the F-111B aircraft. In addition, Grumman would also build the F-111A's aft fuselage and the landing gear. The first test F-111A was powered by YTF30-P-1 turbofans and used a set of ejection seats, since the escape capsule was not yet available. It first flew on 21 December 1964. The first F-111B was also equipped with ejection seats and first flew on 18 May 1965. To address stall issues in certain parts of the flight regime, the F-111's engine inlet design was modified in 1965–66, ending with the "Triple Plow I" and "Triple Plow II" designs. The F-111A achieved a speed of Mach 1.3 in February 1965 with an interim intake design.

The weight goals for both F-111 versions proved to be overly optimistic. Excessive weight plagued the F-111B throughout its development. The prototypes were far over the requirement weight. Design efforts reduced airframe weight but were offset by the addition of the escape capsule. The additional weight made the aircraft underpowered. Lift was improved by changes to the wing control surfaces. A higher thrust version of the engine was planned. During the congressional hearings for the aircraft, Vice Admiral Thomas F. Connolly, then Deputy Chief of Naval Operations for Air Warfare, responded to a question from Senator John C. Stennis as to whether a more powerful engine would cure the aircraft's woes, saying, "There isn't enough power in all  to make that airplane what we want!" With the F-111B program in distress, Grumman began studying improvements and alternatives. In 1966, the Navy awarded Grumman a contract to begin studying advanced fighter designs. Grumman narrowed down these designs to its Model 303 design. With this the F-111B's end appeared near by mid-1967. By May 1968 both Armed Services committees of Congress voted not to fund production and in July 1968 the DoD ordered work stopped on F-111B. A total of seven F-111Bs were delivered by February 1969.

The F-111B's replacement, the , which derived from Grumman's initial Model 303 design, reused the TF30 engines from the F-111B, though the Navy planned on replacing them with an improved engine later. Although lighter than the F-111B, it was still the largest and heaviest U.S. fighter to takeoff and land from an aircraft carrier. Its size was a consequence of the requirement to carry the large AWG-9 radar and AIM-54 Phoenix missiles, both from the F-111B, while exceeding the F-4's maneuverability. While the F-111B was armed only for the interceptor role, the Tomcat incorporated an internal M61 Vulcan cannon, provisions for Sidewinder and Sparrow air-to air missiles, and provisions for bombs. While the F-111B did not reach service, land-based, non-fighter F-111 variants were in service with the  for many years, and with the Royal Australian Air Force until 2010.
The F-111B was an all-weather interceptor aircraft intended to defend U.S. Navy carrier battle groups against bombers and anti-ship missiles. The F-111 features.variable geometry wings, an internal weapons bay and a cockpit with side by side seating. The cockpit is part of an escape crew capsule. The wing sweep varies between 16 degrees and 72.5 degrees (full forward to full sweep).[27] The airframe consisted mostly of aluminum alloys with steel, titanium and other materials also used. The fuselage is a semi-monocoque structure with stiffened panels and honeycomb sandwich panels for skin. The F-111B was powered by two Pratt & Whitney TF30 afterburning turbofan engines and included the AN/AWG-9 radar system for controlling the AIM-54 Phoenix air-to-air missiles. Poor visibility over the nose made the aircraft more difficult to handle for carrier operations.The F-111 offered a platform with the range, payload, and Mach-2 performance to intercept targets quickly, but with swing wings and turbofan engines, it could also loiter on station for long periods. The F-111B would carry six AIM-54 Phoenix missiles, its main armament. Four of the Phoenix missiles mounted on wing pylons and two in the weapons bay. The missile pylons added significant drag when used

Flight tests on the F-111B continued at NAS Point Mugu, California and NAWS China Lake, California even after the program had been terminated. In July 1968, the pre-production F-111B Bureau Number 151974, was used for carrier trials aboard USS Coral Sea. The evaluation was completed without issue.Hughes continued Phoenix missile system development with four F-111Bs. In all, two F-111Bs were lost in crashes and a third seriously damaged. The F-111B's last flight was with 151792 from California to New Jersey in mid-1971. The seven F-111Bs flew 1,748 hours over 1,173 flights.
F-111B numbers 1 to 3 were initial prototypes; and No. 4 and 5 were prototypes with lightened airframes. No. 6 and 7 had lightened airframes and improved TF30-P-12 engines and were built to near production standard. These were also approximately 2 feet (0.6 metres) longer due to an added section between the cockpit and radome. The first five aircraft included Triple Plow I intakes. The last two had Triple Plow II intakes. The first three B-models were fitted with ejection seats and the remainder included the escape crew capsule.

1-151970 Prototype with heavy airframe, TF30-P-3 engines. After flight test use was scrapped in December 1969. 
2-151971 Prototype with heavy airframe, TF30-P-3 engines. Used for Hughes missile testing. Lost in a crash on 11 September 1968.
3-151972 Prototype with heavy airframe, TF30-P-3 engines. Was damaged and retired. Was used for jet blast testing at NATF, NAES Lakehurst, NJ and was probably scrapped there.
4-151973 Prototype with lightened airframe, TF30-P-3 engines. Destroyed in double engine failure crash on 21 April 1967.
5-151974 Prototype with lightened airframe, TF30-P-3 engines. Crash landed at NAS Point Mugu, CA in October 1968. Was dismantled at NAS Moffett Field, CA in 1970.
6-152714 Pre-production version, TF30-P-12 engines. Used for Hughes missile tests. Retired in 1969. Removed from inventory in 1971 and used for parts. Was photographed in 2008 in a Mojave, California scrapyard.
7-152715 Pre-production version, TF30-P-12 engines. Retired and stored at NAWS China Lake, CA (awaiting restoration).