The FB-111A was the all-weather strategic bombing version of the F-111, intended as an interim successor to the B-52 and B-58 of the Strategic Air Command. It was initially developed as Weapon System 129A.
The FB-111A differed from the F-111A primarily in having a longer fuselage (75 feet 7 inches as compared to 73 feet 5 1/2 inches) to accommodate the additional fuel required for its strategic mission. In order to provide a longer range and greater load-lifting capability, the FB-111A had the extended wing of the F-111B (unfolded span of 70 feet as compared to 63 feet). It also had a stronger undercarriage and landing gear, and was powered by TF30-P-7 turbofan engines. It featured the Mark IIB avionic subsystem planned for the F-111E, which comprised an improved F-111A attack radar, an inertial navigation system, digital computers, plus some advanced displays of the later Mark II that equipped the delayed F-111D
The FB-111A was actually the first F-111 version to fly with the new Triple Plow II air intakes, beginning with the third example (67-0161). The Triple Plow II intakes were mounted four inches farther from the airframe in order to improve the boundary layer "plow", and the translating cowl was replaced by a series of blow-in doors which fed additional air to the engines during takeoff or when the aircraft was moving slowly.
The development of the FB-111A was prompted by the slow progress of the Advanced Manned Strategic Aircraft (AMSA) program and by fears that fatigue failures in the B-52 fleet might come earlier than expected. A proposal to resume production of the Convair B-58 Hustler was rejected as being too costly. In the spring of 1963, the Air Force turned to General Dynamics for a solution to its problem. In November of 1963, General Dynamics responded with a suggestion for two strategic versions of the F-111A. In order to hasten availability, the Air Force decided on June 2, 1965 that the least modified version was the one that they would go with. The designation FB-111A was applied, which is sort of curious since the design was basically a modified F-111A, which would have suggested that the designation should have been BF-111A.
The Air Force initially planned to order 263 FB-111As (210 to equip 14 squadrons, plus 20 for combat crew training and the remaining 33 for support and testing). It wanted them in service quickly, the first FB-111As being expected to be operational as early as fiscal year 1969.
Secretary of Defense Robert McNamara publically announced plans to develop the FB-111A on December 10, 1965. However, the implementation of the program was postponed until February 1966, when the FB-111A had been added to the basic F-111A RDT&E contract and Congress had approved the funds. In January of 1966, Secretary McNamara asked the Air Force to begin contract definition on Mark II avionics systems for both the FB-111A and the delayed F-111D, with maximum commonality being a key requirement. The primary weapon of the FB-111A was to be the Boeing-designed AGM-69A Short-Range Attack Missile (SRAM).
A modified RDT&E F-111A (serial number 63-9783) was converted as the prototype of the FB-111A and flew for the first time on July 30, 1967. It achieved Mach 2 on its first test flight.
Pending the availability of the P-7 engine, it was decided that the first few FB-111As would receive P-12A engines (the USAF version of the Navy P-12 engine that was used in the F-111B) and these engines would subsequently be brought up to the P-7 configuration once the aircraft was in service.
The first production FB-111A aircraft flew on July 13, 1968. It was accepted by the Air Force on August 30, 1968. A second FB-111A was delivered on October 25. These two planes were powered by TF30-P-12A engines. Problems with the Mark IIB avionics slowed further deliveries, with the Air Force not accepting its next FB-111A until June 23, 1969. This aircraft featured a fully-developed Triple Plow II air diverter, a complete Mark IIB avionics system, and the new P-7 engines.
The first 6 FB-111A production aircraft were used for testing. Category III tests did not finish until July 31, 1972.
A total of 263 planes was projected when the FB-111A program began. This was reduced to 126 on November 28, 1968 because of rising costs and production delays with the basic F-111 program. The final cut took place on March 16, 1969, with the total FB-111A order being reduced to 76.
On October 8, 1969, the 7th FB-111A entered service with the 4007th Combat Crew Training Squadron of the 340th Bomb Group at Carswell AFB. Even though the FB-111A was officially declared operational, it had yet to reach the combat forces. After reaching operational capability, the 4007th CCTS relocated to Plattsburg and became part of the 380th Strategic Aerospace Wing.
The primary offensive armament of the FB-111A was the Boeing-designed AGM-69A SRAM, a missile designed primarily to neutralize enemy defense systems such as radars, SAMs, and other anti-aircraft systems. The launch weight of the SRAM was 2230 pounds, and it was powered by a two-pulse solid-fuel rocket motor. Maximum speed was Mach 2.8-3.2, and the range varied from 35 to 105 miles, depending on the mission. The guidance system consists of a Singer Kearfott inertial guidance operating in conjunction with a Delco on-board computer. Various attack trajectories could be chosen, ranging from semi-ballistic to terrain-following. During an actual operational mission, the bombardier would select each missile in turn, update the inertial guidance system, then would let the missile drop. The rocket motor would then fire and accelerate the missile to Mach 3, fast enough to fly and steer with body lift and three tail fins. When the missile neared the target, the second propulsion stage would then ignite for the final run in to the target. The SRAM carried a W6 nuclear warhead with an explosive yield of 200 kilotons.
FB-111A testing of the SRAM began on March 27, 1970. Initial test started poorly--in almost a year, there were only seven successes out of 11 launches. However, by early 1971, the results began to get better, with the final score being 15 successes out 19 launches during the entire test series.
In January 1971, the FB-111A achieved initial operational capability with the 509th Bomb Wing (393 and 715 Squadrons) based at Pease AFB in New Hampshire. After many difficulties, the 509th was finally declared fully combat-ready in October of 1971. The 380th Strategic Aerospace Wing (528 and 529 Squadrons, plus the 4007th Combat Crew Training Squadron) at Plattsburg AFB in New York became combat ready in 1972. These were the only two SAC wings to receive the FB-111A.
The last production FB-111A was delivered to SAC on June 30, 1971.
The FB-111A could carry two AGM-69A SRAMs in the internal weapons bay along with two more on the inner underwing pylons. Typically, four 600-US gallon drop tanks were carried on the outermost underwing pylons, although the SRAMS carried underneath the innermost underwing pylons could be replaced by another pair of 600-gallon drop tanks, bringing the total number of drop tanks to six. In addition, fuel tanks could be installed inside the weapons bay. Two conformal fuel tanks could be installed, with the left side carrying 285 gallons and the right side carrying 300 gallons, for a total of 585 gallons. The non-swiveling outer pylons are intended for subsonic flight only and are jettisoned when wing sweep exceeds 26 degrees. Alternatively, up to 24 750-pound conventional bombs could be carried externally. The FB-111A could also carry six gravity nuclear weapons or a B77 nuclear bomb. A total offensive load of 35,500 pounds could be carried.
The FB-111A carries the APQ-144 forward-looking attack radar, which was derived from the APQ-113 of the F-111A. It adds a beacon mode, a photo recording capability, and a north-oriented display.
Landing gear malfunctions persisted throughout mid-1971 and were finally solved by a simple field modification. In late 1971, weapons delivery was still marginal, reflecting failures in the inertial navigation system. There were some problems with engine flameouts following use of the afterburner, these being probably caused by moisture in the engine sensing line.
In April 1972, new SRAM-carrying equipment was installed on the FB-111A.
In November 1970, the FB-111A took top honors in bombing and navigation during SAC's competition at McCoy AFB in Florida. The first overseas deployment of the FB-111A was the entrance of two Pease FB-111As in a Royal Air Force bombing and navigation meet at RAF Marham.
As the Rockwell B-1B Lancer came into service, the FB-111A became redundant to SAC needs, and most surviving FB-111As were converted into ground attack configuration and assigned to training units operating out of Cannon AFB in New Mexico. During 1988, the designation F-111G was adopted for the FB-111As that were to be converted eventually to serve in the tactical role when displaced from SAC.
In June of 1990, the SRAM missiles were removed from the inventory because of safety concerns regarding the integrity of their W69 nuclear warheads in the event of a fire. After that, the FB-111As stood alert with only gravity bombs.
Serials of the FB-111A:
67-0159/0163 67-7192/7196 68-0239/0292 69-6503/6514
Specification of the FB-111A:
Engines: Two Pratt & Whitney TF30-P-7 turbofans, 12,500 lb.s.t. dry and 20,350 lb.s.t. with afterburner. Performance: Maximum speed (clean): 1453 mph at 50,000 feet, 1320 mph at 36,000 feet, 838 mph at sea level. Initial climb rate (clean) 23,418 feet per minute. Service ceiling: 50,263 feet. Range: 2500 miles with four SRAMs and internal fuel only. Maximum ferry range: 4786 miles with six 600-US gall. auxiliary fuel tanks mounted on underwing pylons. Weights: 47,980 pounds empty, 119,250 pounds gross. Dimensions: Wingspan 70 feet 0 inches (minimum sweep), 33 feet 11 inches (maximum sweep), length 75 feet 7 inches, height 17 feet 0 inches. Internal fuel capacity of 5010 US gallons (total of 5623 gallons with internal weapons-bay fuel tanks installed). With six 600 US gallon underwing drop tanks fitted, a total of 9223 US gallons of fuel can be carried. Armed with up to six Boeing AGM-69A SRAMs on external pylons or in internal weapons bay, or a conventional ordnance load of up to 37,500 pounds of bombs, rockets, or fuel tanks.
Sources:
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United States Military Aircraft Since 1909, Gordon Swanborough and
Peter M. Bowers, Smithsonian, 1989.
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General Dynamics Aircraft and their Predecessors, John Wegg,
Naval Institute Press, 1990.
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Post-World War II Fighters: 1945-1973, Marcelle Size Knaac,
Office of Air Force History, 1986.
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The American Fighter, Enzo Angelucci and Peter Bowers,
Orion, 1987.
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The World Guide to Combat Planes, William Green, Macdonald, 1966.
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Modern Air Combat, Bill Gunston and Mike Spick, Crescent Books, 1983.
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The Illustrated Encyclopedia of Aircraft Armament, Bill Gunston,
Orion, 1988.
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Flying the Frontiers--NACA and NASA Experimental Aircraft, Arthur
Pearcy, Naval Institute Press, 1993.
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F-111 Aardvark--USAF's Ultimate Strike Aircraft, Tony Thornborough,
Osprey Aerospace, 1993.
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F-111 Aardvark, Hans Halberstadt, Specialty Press, 1992.
- E-mail from Kevin Larios on internal conformal fuel tanks in the weapons bay.
