General Dynamics F-111 Aardvark

The General Dynamics F-111 Aardvark is a retired, supersonic, medium-range fighter-bomber. Production models of the F-111 had roles that included attack (e.g., interdiction), strategic bombing (including nuclear weapons capabilities), reconnaissance, and electronic warfare. Its name "Aardvark" comes from a long-nosed, insect-eating African animal.

Developed in the 1960s by General Dynamics under Robert McNamara's TFX Program, the F-111 pioneered variable-sweep wings, afterburning turbofan engines, and automated terrain-following radar for low-level, high-speed flight. Its design influenced later variable-sweep wing aircraft, and some of its advanced features have become commonplace. The F-111 suffered problems during initial development, largely related to the engines. A multirole carrier-based fighter/long-range interception variant intended for the United States Navy, the F-111B, was canceled before production. Several specialized models, such as the FB-111 strategic bomber and the EF-111 electronic warfare aircraft, were also developed.

The F-111 entered service in 1967 with the United States Air Force (USAF). In the meantime, the Australian government had ordered the F-111C, to replace the English Electric Canberra then used by the Royal Australian Air Force (RAAF). The F-111C entered service with the RAAF in 1973.

As early as March 1968, the USAF was deploying F-111s into active combat situations; the type saw heavy use during the latter half of the Vietnam War to conduct low-level, ground-attack missions, flying in excess of 4,000 combat missions while incurring only six combat losses in the theater. The F-111s also participated in the Gulf War (Operation Desert Storm) in 1991; the F-111Fs completed 3.2 successful strike missions for every unsuccessful one, better than any other US strike aircraft used in the operation. RAAF F-111s never saw offensive action, but were deployed periodically as a deterrent, such as for the Australian-led International Force East Timor.

Being relatively expensive to maintain amid post-Cold War budget cuts, the USAF elected to retire its F-111 fleet during the 1990s; the last F-111Fs were withdrawn in 1996, while the remaining EF-111s also departed in 1998. The F-111 was replaced in USAF service by the Strike Eagle for medium-range, precision strike missions, while the supersonic bomber role has been assumed by the B-1B Lancer. The RAAF continued to operate the type until December 2010, when the last F-111C was retired; its role was transitioned to the Boeing F/A-18E/F Super Hornet as an interim measure until the Lockheed Martin F-35 Lightning II became available.

Development

Early requirements

The May 1960 U-2 incident, in which an American CIA U-2 reconnaissance plane was shot down over the USSR, stunned the United States government. Besides greatly damaging US–Soviet relations, the incident showed that the Soviet Union had developed a surface-to-air missile that could reach aircraft above 60,000 ft (18,000 m). Consequently, the USAF Strategic Air Command (SAC) and the RAF Bomber Command's plans to send subsonic, high-altitude Boeing B-47 Stratojet and V bomber formations into the USSR were realized to be much less viable.

By 1960, SAC had begun moving to low-level penetration, which greatly reduced radar detection distances. At the time, SAMs were ineffective against low-flying aircraft, while interceptor aircraft had less of a speed advantage at low altitudes. The USAF's Tactical Air Command (TAC) was largely concerned with the fighter-bomber and deep strike/interdiction roles. TAC was in the process of receiving its latest design, the Republic Thunderchief, which was designed to deliver nuclear weapons fast and far, but required long runways. A simpler variable-geometry wing configuration with the pivot points farther out from the aircraft's centerline was reported by NASA in 1958, which made swing-wings viable. This led USAF leaders to encourage its use.

In June 1960, the USAF issued specification SOR 183 for a long-range, interdiction/strike aircraft able to penetrate Soviet air defenses at very low altitudes and high speeds. Specifically, it was to be capable of at least of low-level flight, half of which was to be at a speed of no less than Mach 1.2. Furthermore, the specification also called for the aircraft to possess short takeoff-and-landing (STOL) capabilities to permit operations from short, unprepared airstrips that had a length of no more than .

Around this time, the United States Navy had been seeking a long-range, high-endurance, fleet air defense fighter to protect its carrier battle groups against long-range antiship missiles launched from Soviet jet bombers and submarines. It would need a more powerful radar and longer-range missiles than the F-4 Phantom II it would replace. The Navy had proposed a subsonic, straight-winged aircraft, the Douglas F6D Missileer in the late 1950s. The Missileer could carry six long-range missiles and loiter for five hours, but would be defenseless after firing its missiles. NASA's simplification made the variable-geometry wings practical. Variable geometry offered high speeds, and maneuverability with heavier payloads, long range, and STOL capability.

Tactical Fighter Experimental

The USAF and Navy were both seeking new aircraft when Robert McNamara was appointed secretary of defense in January 1961. Both sought high-supersonic, twin-engined, two-seat aircraft that could carry heavy armament and fuel loads and probably use variable-geometry wings. On 14 February 1961, McNamara formally directed the services to study the development of a single aircraft that would satisfy both requirements. Early studies indicated that the best option was to base the design on the USAF requirement, and use a modified version for the Navy. In June 1961, Secretary McNamara ordered the go-ahead of Tactical Fighter Experimental (TFX), despite USAF and Navy efforts to keep their programs separate. According to aviation author Peter E. Davis, military officials were disconcerted by McNamara's focus on compromised requirements for financial reasons.

thumb|The side-by-side seating adopted in the F-111

The two services could agree only on swing-wing, two-seat, twin-engined design features. The USAF wanted a tandem-seat aircraft for low-level penetration ground attack, while the Navy wanted a shorter, high-altitude interceptor with side-by-side seating to allow the pilot and radar operator to share the radar display. 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 an approximate length of . The Navy had less strenuous requirements: 6 g with Mach 2 speed at altitude and high subsonic speed (about Mach 0.9) at low level with a length of . The Navy also wanted the aircraft with a nose large enough for a diameter radar dish.

McNamara developed a basic set of requirements for TFX based largely on the USAF's requirements, and on 1 September 1961, ordered the USAF to develop it. In December, proposals were received from Boeing, General Dynamics, Lockheed, McDonnell, North American, and Republic. The evaluation group found all the proposals lacking, but Boeing and General Dynamics were selected to submit enhanced designs. Boeing's proposal was recommended by the selection board in January 1962, with the exception of the engine, which was not considered acceptable. The board also directed alterations to radar and missile storage and a switch from ejection seats to a crew-escape capsule. Both companies provided updated proposals in April 1962. USAF reviewers favored Boeing's offering, while the Navy found both submissions unacceptable for its operations. A congressional investigation into the procurement process was conducted, but did not change the selection. On 1 May 1964, the definitized contract was issued for the program, including flight testing, spares, ground equipment, training devices, static and fatigue test data, and the production of an initial 23 F-111 aircraft; it was structured as a fixed-price incentive-fee (FPIF) contract with a ceiling price of $529 million, along with provisions for deficiency correction among other operational clauses and performance criteria.

Design phase

General Dynamics' design team was led by Robert H. Widmer. Recognizing its lack of experience with carrier-based fighters, General Dynamics teamed with Grumman in November 1963 for the assembly and testing of the F-111B. In addition, Grumman would also build the aft fuselage and the landing gear of the F-111A. The General Dynamics and Grumman team faced ambitious requirements for range, weapons load, and aircraft weight. Thus, the F-111 was designed to incorporate numerous features that were new to production military aircraft, such as variable-geometry wings and afterburning turbofan engines. This use of unfamiliar features has been attributed as a major cause of the aircraft's protracted development and weight increases.

The F-111A and F-111B shared the same airframe structural components and Pratt & Whitney TF30-P-1 turbofan engines. They featured side-by-side crew seating in an escape capsule as required by the Navy. The F-111B's nose was shorter as the aircraft could fit on existing carrier elevator decks, and had wingtips to improve on-station endurance time; it also carried an AN/AWG-9 pulse-Doppler radar to guide its AIM-54 Phoenix missiles. The USAF's F-111A would be equipped with the AN/APQ-113 attack radar and the AN/APQ-110 terrain-following radar and air-to-ground armament.

During September 1963, the F-111A mockup was inspected. Early flights of the F-111, which included supersonic flights, demonstrated favorably simplistic maintenance requirements, among other qualities.

Various changes to the program were enacted throughout 1965; this was chiefly in response to a steep climb in unit costs from $4.5 million to $6 million. On 10 May 1967, a new, multiyear FPIP contract replaced the prior procurement process, increasing the total aircraft on order to 493 F-111s of multiple models, including 23 F-111Bs intended for the US Navy, 24 F-111Cs for the Royal Australian Air Force, and 50 F-111Ks intended for the Royal Air Force.

Early flights of the F-111 were troubled by compressor surges and stalls across certain portions of the flight regimen. General Dynamics had elected to use an uncommon, spike-shaped, variable intake for the engine for the performance. During February 1965, the F-111A achieved a speed of Mach 1.3 while flying with an interim intake design.

Separately, cracks in the F-111's wing attachment points were first discovered in 1968 during ground fatigue testing; during the following year, the crash of an F-111 was attributed to a cracked wingbox. The resolution involved the redesigning of the attachment structure and necessitated testing to ensure adequate design and workmanship. On 31 July 1970, the grounding was lifted. Category I flight testing of the F-111A, which had started in 1964, continued through to 31 March 1972. Australia would procure its own model, the F-111C. Subsequently, the improved F-111E, F-111D, and F-111F models were developed for the USAF. The strategic bomber FB-111A and the EF-111 electronic-warfare versions were later developed for the USAF. Production of the F-111 ended in 1976, following the completion of 563 aircraft. The F-111 featured variable-geometry wings, an internal weapons bay, and a cockpit with side-by-side seating. The cockpit was part of an escape crew capsule. The wing sweep varied between 16 and 72.5° (full forward to full sweep). The wing included leading-edge slats and double-slotted flaps over its full length. The airframe was made up mostly of aluminum alloys with steel, titanium, and other materials used in places. The fuselage was made of a semimonocoque structure with stiffened panels and honeycomb structure panels for skin.

The F-111 used a three-point landing-gear arrangement, with a two-wheel nose gear and two single-wheel main landing-gear units. The landing-gear door for the main gear, which was positioned in the center of the fuselage, also served as a speed brake in flight. Most F-111 variants included a terrain-following radar system connected to the autopilot. The aircraft was powered by two Pratt and Whitney TF30 afterburning turbofan engines. The F-111's variable-geometry wings, escape capsule, terrain-following radar, and afterburning turbofans were new technologies for production aircraft.

Armament

The armament included a 20 mm cannon and 5,000 lb of bombs internal; added pylons could carry up to 25,000 lb of bombs or two nuclear weapons internal and four AGM-69 SRAM nuclear weapons external.

Weapons bay

thumb|F-111 cockpit before a night flight

The F-111 featured an internal weapons bay that could carry bombs, a removable 20 mm M61 cannon, or auxiliary fuel tanks.

The F-111C and F-111F were equipped to carry the AN/AVQ-26 Pave Tack targeting system on a rotating carriage that kept the pod protected within the weapons bay when not in use. Pave Tack featured a forward-looking infrared  sensor, optical camera, and laser rangefinder/designator. The Pave Tack pod allowed the F-111 to designate targets and drop laser-guided bombs on them. Australian RF-111Cs carried a pallet of sensors and cameras for aerial reconnaissance use.

The FB-111 could carry two AGM-69 SRAM air-to-surface, nuclear missiles in its weapons bay. General Dynamics tested an arrangement with two AIM-9 Sidewinder air-to-air missiles carried on rails in a trapeze arrangement from the bay, but this was not adopted.

External ordnance

thumb|F-111 external payload of [[Matra Durandal concrete-penetration bombs|alt=Closeup view of cylindrical bombs and ordnance carried under a mostly green aircraft wing]]

Each wing was equipped with four underwing pylons. The inner two pylons on each wing rotated to align with the fuselage, while the outer two were fixed. Each pylon had a capacity of . Various bombs and missiles could be carried on the pylons. Auxiliary fuel drop tanks with capacity each could be fitted.

The design of the F-111's fuselage prevented the carriage of external weapons under the fuselage, but two stations were available on the underside for electronic countermeasures pods or datalink pods; one station was on the weapons bay, and the other was on the rear fuselage between the engines.

Tactical F-111s were fitted with shoulder rails on the four inner swiveling pylons to mount AIM-9 Sidewinder air-to-air missiles for self-defense. FB-111As could carry the same conventional ordnance as the tactical variants, but their wing pylons were more commonly used for either fuel tanks or strategic nuclear gravity bombs. They could carry up to four AGM-69 SRAM nuclear missiles on the pylons.

Historical significance

The F-111 was the first production variable-geometry wing aircraft. The US Navy's role intended for the F-111B was instead filled by another variable-geometry design, the Grumman F-14 Tomcat.

Operational history

US Air Force

thumb|right|Combat Lancer F-111As over Southeast Asia in 1968|alt=Two green jet aircraft flying together, right of wing. Further out in the background is another jet aircraft.

The first of six initial-production F-111s was delivered on 17 July 1967 to fighter squadrons at Nellis Air Force Base. These aircraft were used for crew training. The 428th Tactical Fighter Squadron achieved initial operational capability on 28 April 1968.

After early testing, a detachment of six aircraft from the 474th Tactical Fighter Wing (Roadrunners) were sent in March 1968 to Southeast Asia for Combat Lancer testing in real combat conditions in the Vietnam War. During the deployment, 55 night missions were flown against targets in North Vietnam, but two aircraft had been lost; 66–0022 was lost on 28 March, and 66-0017 on 30 March. Replacement aircraft left Nellis, but the loss of a third F-111A (66-0024) on 22 April halted F-111A combat operations. The squadron returned to the United States in November. The cause of the first two losses is unknown, as the wreckages were never recovered. The third loss was traced to a failure of a hydraulic control-valve rod for the horizontal stabilizer, which caused the aircraft to pitch up uncontrollably. Further inspection of the remaining fleet of F-111As revealed 42 aircraft with the same potential failures. This failure could also have contributed to the two earlier losses had the failure caused a pitch down while at low altitude. The 474 TFW was not fully operational until 1971.

The word aardvark is Afrikaans for "earthpig" and reflects the look of the long nose of the aircraft that might remind one of the nose of the aardvark. The origin of the name has been attributed to F-111A Instructor Pilot Al Mateczun in 1969, as the aircraft had not received an official USAF name.

During September 1972, the F-111 returned to Southeast Asia, stationed at Takhli Air Base, Thailand. F-111As from Nellis AFB participated in the final month of Operation Linebacker and later flew 154 low-level missions in the Operation Linebacker II aerial offensive against the North Vietnamese, They also supported regional aerial operations against other communist forces such as Operation Phou Phiang III during the Laotian Civil War. Crews described their flying in Vietnam as "speed is life", "one pass, haul ass", and "you do more than one pass in a target area you die". The F-111's ability with terrain-following radar ("the best in the fighter world", according to F-111 pilot Richard Crandall) to fly as low as above ground level at or faster in most weather conditions made it very effective; missions did not require tankers or ECM support, and they could operate in weather that grounded most other aircraft. One F-111 could carry the bomb load of four McDonnell Douglas F-4 Phantom IIs. The worth of the new aircraft was beginning to show: F-111s flew more than 4,000 combat missions in Vietnam with only six combat losses.

From 30 July 1973, F-111As of the 347th Tactical Fighter Wing (347th TFW) were stationed at Takhli Air Base. The 347th TFW conducted bombing missions in Cambodia in support of Khmer Republic forces until 15 August 1973, when US combat support ceased in accordance with the Case–Church Amendment. The 347th TFW was stationed at Korat Royal Thai Air Force Base from 12 July 1974 until 30 June 1975. In May 1975, 347th TFW F-111s provided air support during the Mayaguez incident.

One of the most unusual missions occurred on 14 February 1986, when two FB-111s of the 509th Bombardment Wing were dispatched from then Pease Air Force Base, New Hampshire, to Tinker Air Force Base, Oklahoma, to pick up a heart for transplant. The aircraft landed at Bradley International Airport to deliver the organ to a waiting ambulance.

thumb|Ground crew prepares an F-111F of the 48th Tactical Fighter Wing for a retaliatory air strike on Libya

On 14 April 1986, 18 F-111s and about 25 Navy aircraft conducted air strikes against Libya under Operation El Dorado Canyon. The 18 F-111s of the 48th Tactical Fighter Wing and four EF-111As from the 20th Tactical Fighter Wing flew what turned out to be the longest fighter combat mission in history.

F-111s participated in the Gulf War (Operation Desert Storm) in 1991. During Desert Storm, F-111Fs completed 3.2 successful strike missions for every unsuccessful one, better than any other US strike aircraft used in the operation. The group of 66 F-111Fs dropped almost 80% of the war's laser-guided bombs, including the penetrating bunker-buster GBU-28. Eighteen F-111Es were also deployed during the operation. Their use in the anti-armor role was dubbed "tank plinking".

Though expensive to operate (Crandall said that the aircraft "was nine percent of Tactical Air Command's fleet, but ate up a whopping 25 percent of the maintenance budget"), the F-111