F-111.net

Early requirements

The May 1960 U-2 incident, in which an American CIA U-2 spy 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 feet (18,000 meters). The United States Air Force Strategic Air Command (SAC) and the RAF Bomber Command's plans to send subsonic, high-altitude B-47 and V bomber formations into the USSR were now 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, and interceptor aircraft had less of a speed advantage at low altitudes. The Air Force'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 F-105 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 Air Force 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. The specification also called for the aircraft to operate from short, unprepared airstrips.In the 1950s, the United States Navy sought a long-range, high-endurance interceptor aircraft to protect its carrier battle groups against long-range anti-ship missiles launched from Soviet jet bombers and submarines. The Navy needed a fleet air defense (FAD) fighter with a more powerful radar, and longer range missiles than the F-4 Phantom II to intercept both enemy bombers and missiles. Seeking a FAD fighter, the Navy started with the subsonic, straight-winged aircraft, the Douglas F6D Missileer in the late 1950s. The Missileer was designed to carry six long-range missiles and loiter for five hours, but would be defenseless after firing its missiles. The program was formally canceled in 1961. The Navy had tried variable geometry wings with the XF10F Jaguar, but abandoned it in the early 1950s. It was NASA's simplification which made the variable geometry wings practical. By 1960, increases in aircraft weights required improved high-lift devices, such as variable geometry wings. Variable geometry offered high speeds, and maneuverability with heavier payloads, long range, and the ability to take off and land in shorter distances

Tactical Fighter Experimental (TFX)

The U.S. Air Force and Navy were both seeking new aircraft when Robert McNam ara was appointed Secretary of Defense in January 1961. The aircraft sought by the two armed services shared the need to carry heavy armament and fuel loads, feature high supersonic speed, twin engines and two seats, 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 Air Force requirement, and use a modified version for the Navy. In June 1961, Secretary McNamara ordered the go ahead of Tactical Fighter Experimental (TFX), despite Air Force and Navy efforts to keep their programs separate.

The side-by-side seating adopted in the F-111The Air Force and the Navy could agree only on swing-wing, two-seat, twin-engine design features. The Air Force 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 Air Force 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 70 ft (21.3 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 the aircraft with a nose large enough for a 48 in (1.2 m) diameter radar dish.McNamara developed a basic set of requirements for TFX based largely on the Air Force's requirements and, on 1 September 1961, ordered the Air Force to develop it. A request for proposals (RFP) for the TFX was provided to industry in October 1961. 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. Switching to a crew escape capsule, instead of ejection seats and alterations to radar and missile storage were also needed. Both companies provided updated proposals in April 1962. Air Force reviewers favored Boeing's offering, while the Navy found both submissions unacceptable for its operations. Two more rounds of updates to the proposals were conducted, with Boeing being picked by the selection board.In November 1962, McNamara selected General Dynamics' proposal due to its greater commonality between Air Force and Navy versions. The Boeing aircraft shared less than half of the major structural components. General Dynamics signed the TFX contract in December 1962. A Congressional investigation followed, but would not change the selection

Design Phase

The F-111A and B variants used 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 8.5 feet (2.59 m) shorter so as to fit on existing carrier elevator decks, and had 3.5-foot-longer (1.07 m) wingtips to improve on-station endurance time. The Navy version would carry an AN/AWG-9 Pulse-Doppler radar and 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 armament. A team of engineers at General Dynamics was led by Robert H. Widmer.Lacking experience with carrier-based fighters, General Dynamics teamed with Grumman for the assembly and testing of the F-111B aircraft. In addition, Grumman would also build the F-111A's aft fuselage and the landing gear. The General Dynamics and Grumman team faced ambitious requirements for range, weapons load, and aircraft weight. The F-111 design also included new features on a production military aircraft, such as variable-geometry wings and afterburning turbofan engines.The F-111A mockup was inspected in September 1963. The first test F-111A was rolled out of Plant 4 of General Dynamics' Fort Worth, Texas facility on 15 October 1964. It was powered by YTF30-P-1 turbofans and used a set of ejector seats as the escape capsule was not yet available. The F-111A first flew on 21 December 1964 from Carswell Air Force Base, Texas, U.S. The first F-111B was also equipped with ejector seats and first flew on 18 May 1965.Initially there were compressor surge and stall issues in certain parts of the flight regime. NASA, the Air Force, and General Dynamics studies resulted in the engine inlet design being 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. Cracks in the F-111's wing attach points were first discovered in 1968 during ground fatigue testing - an F-111 crashed the following year due to this issue. The attach structure required redesign and testing to ensure adequate design and workmanship. Flight testing of the F-111A ran through 1973.The F-111B was canceled by the Navy in 1968 due to weight and performance issues, along with the need for additional fighter requirements. The F-111C model was developed for Australia. Subsequently, the improved F-111E, F-111D, F-111F models were developed for the U.S. Air Force. The strategic bomber FB-111A and the EF-111 electronic warfare versions were later developed for the USAF. Production ended in 1976 after 563 F-111 aircraft were built.

Design overview

The F-111 was an all-weather attack aircraft, capable of low-level penetration of enemy defenses to deliver ordnance on the target. 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 degrees and 72.5 degrees (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 aluminium alloys with steel, titanium and other materials used in places. The fuselage was made of a semi-monocoque 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 & 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.

Weapons bay

The F-111 featured an internal weapons bay that could carry bombs, a removable 20 mm M61 cannon or auxiliary fuel tanks. For bombs, the bay could hold two 750 lb (340 kg) M117 conventional bombs, one nuclear bomb or practice bombs. The F-111B for the US Navy was to carry two AIM-54 Phoenix long-range air-to-air missiles in the bay. The cannon had a large 2,084-round ammunition tank, and its muzzle was covered by a fairing; however, it was rarely fitted on F-111s.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 (FLIR) 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 trialed 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. Early F-111 models had radars equipped to guide the AIM-7 Sparrow medium-range air-to-air missile, but it was never fitted.

External ordnance

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 5,000 pounds (2,300 kilograms). Various bombs and missiles could be carried on the pylons. Auxiliary fuel drop tanks with 600 US gallons (2,300 litres) 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 (ECM) pods and/or datalink pods; one station was on the weapons bay, and the other on the rear fuselage between the engines. The F-111's maximum practical weapons load was limited, since the fixed pylons could not be used with the wings fully swept.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. Australian F-111Cs were equipped to launch the Harpoon anti-ship missile, and the Popeye stand-off missile. 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.

Operational history, USAF

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. 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 (474th TFW 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. It turned out that 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. It is speculated that this failure could also have contributed to the two earlier losses had the failure caused a pitch down while at low altitude. It was not until 1971 that 474 TFW was fully operational.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 name is attributed to F-111A Instructor Pilot Al Mateczun in 1969, as the aircraft had not received an official Air Force name.September 1972 saw the F-111 back in 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, who called the aircraft "Whispering Death". They also supported regional aerial operations against other communist forces such as Operation Phou Phiang III during the Laotian Civil War in Laos. 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 200 feet above ground level at 480 knots 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.
On 14 April 1986, 18 F-111s and approximately 25 Navy aircraft conducted air strikes against Libya under Operation El Dorado Canyon. The 18 F-111s of the 48th Tactical Fighter Wing and 4 EF-111As from the 20th Tactical Fighter Wing flew what turned out to be the longest fighter combat mission in history. The round-trip flight between RAF Lakenheath/RAF Upper Heyford, United Kingdom and Libya of 6,400 miles (10,300 km) spanned 13 hours. One F-111 was lost over Libya and crashed into the Mediterranean Sea, probably shot down.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 U.S. 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. The F-111s were credited with destroying more than 1,500 Iraqi tanks and armored vehicles. Their use in the anti-armor role was dubbed "tank plinking".The F-111 was in service with the USAF from 1967 through 1998. The FB-111s were operated by Strategic Air Command from 1969 before conversion to F-111G and transferred to Air Combat Command (ACC) until their retirement in 1993. At a ceremony marking the F-111's USAF retirement, on 27 July 1996, it was officially named Aardvark, its long-standing unofficial name. The USAF retired the EF-111 electronic warfare variant in 1998.Royal Australian Air Force

Operational history, Royal Australian Air Force

The Australian government ordered 24 F-111C aircraft to replace the RAAF's English Electric Canberras in the bombing and tactical strike role. While the first aircraft was officially handed over in September 1968, structural issues delayed the entry into service. The first F-111C was accepted at Nellis Air Force Base on 15 March 1973. The RAAF's first six F-111Cs arrived at Amberley on 1 July 1973, and three subsequent flights of six F-111s arrived on 27 July, 28 September and 4 December. F-111Cs were allocated to No. 1 Squadron and No. 6 Squadron, under the control of No. 82 Wing. In Australia, the F-111 was affectionately known as the "Pig", due possibly to its long nose, terrain-following ability, and/or the origins of the word aardvark (i.e. a loanword in English from Afrikaans, in which it originally meant "earth-pig").

Four Australian F-111s flying towards Nellis Air Force Base after a refueling exercise during Red Flag 2006.The purchase proved to be highly successful for the RAAF. Although it never saw combat, the F-111C was the fastest, longest range combat aircraft in Southeast Asia. Aviation historian Alan Stephens has written that they were "the preeminent weapons system in the Asia-Pacific region" throughout their service and provided Australia with "a genuine, independent strike capability". Benny Murdani, Indonesian defense minister in the 1980s, told his Australian counterpart Kim Beazley that when others became upset with Australia during Indonesian cabinet meetings, Murdani told them "Do you realise the Australians have a bomber that can put a bomb through that window on to the table here in front of us?"Australian F-111s were bombed-up at RAAF Base Tindal ready to attack Indonesian forces and command systems during the tension in 1999 during the establishment of East Timor's independence and the deployment of the Australian-led International Force for East Timor.In 2006, an RAAF F-111 was chosen to scuttle the North Korean ship  Pong Su that had been seized in 2003 in one of the largest drug hauls in Australia. The Pong Su was sunk on 23 March 2006 by two GBU-10 Paveway II laser-guided bombs.The drawdown of the RAAF's F-111 fleet began with the retirement of the F-111G models operated by No. 6 Squadron in late 2007. There was controversial procurement of 24 F/A-18F Super Hornets as an interim replacement for the F-111s while the F-35 program suffered delays. One of the reasons given for the F-111s' retirement was the high maintenance time required for every flight hour; Crandall said that the USAF's F-111 "was nine percent of Tactical Air Command's fleet but ate up a whopping 25 percent of the maintenance budget". The last F-111s were retired on 3 December 2010.