FB-111 Strategic Bomber

By on Monday, September 24th, 2007

The FB-111A, manufactured by the General Dynamics in December 1966, evolved in a bid to replace the B-58 and to have the mission flexibility the B-58 lacked. The swing wing design of the aircraft was proposed to meet an Air Force requirement for a medium-range bomber capable of high and low altitude supersonic flight.

With a maximum takeoff gross weight of 114,000 pounds, the FB-111A was 75.5 feet long, 17 feet high, and had a wing span of 34 feet with the wings fully swept or 70 feet with the wings forward. The bomber version had a 3.5 foot extension on each wingtip for range improvement, additional avionics equipment, new engines, and a reinforced landing gear and fuselage to accommodate a heavier gross weight. The FB-111A was a two-engine jet bomber with afterburner. The engines ware integral to the fuselage. The variable geometry wings were attached high on the fuselage and can be swept back from 16 to 72.5. The crew consists of a pilot and a navigator sitting side by side in a cockpit that is designed as an emergency escape module.

The initial flight of FB-111A took the sky in July 1967 with the first production aircraft delivered in August 1968. The F-111 had cost overrun problems and bad publicity; so only 76 were built. It was later labeled as an interim bomber to provide a better, low-level penetration capability until a B-52 replacement was built.

Although the range of the FB-111A is better than the fighter version, it is still only a medium-range bomber that requires both additional tanker support and preferential basing. Due to its small size, there is little space for modification, thereby limiting adaptability and flexibility. For example, it is impossible to expand its ECM capability to counter new threats or to enhance its offensive avionics by adding new technology electronics. There are, however, some advantages to the FB-111A over previous medium-range bombers. Its design is optimized for performance both at high and low altitude. It has a smaller RCS with a terrain following capability, making it a very effective low altitude penetrator. It also has an improved survivability due to its ability to get airborne quickly and away from its ground alert location. The two engines of the FB-111A can be started quickly, and it has a shorter takeoff roll than its predecessors. Further, the payload is not as limited as the B-58 since the FB-111A can carry up to 24 conventional bombs. However, this requires external carriage which restricts the wing sweep and degrades the range. The nuclear payload is two internal SRAM/gravity bombs and up to four external pylon-mounted weapons.

The cost overruns, bad publicity and range limitation stacked poorly in comparison to the B-52 and the new B-1 on the drawing board resulted in the FB-111 program being scaled back. The FB-111 however could adapt to different roles because mission flexibility was designed in, but its very size limited its range, modification space available, and payload. To overcome some of these drawbacks, SAC initiated several studies to stretch the FB-111A to improve its capabilities, but none resulted in a modification program. The modified design would have lengthened the existing FB-111A so as to increase fuel load capacity, space available for electronics, and internal and external weapons payload. The more powerful F-101 engine would have replaced the existing engines. It was estimated that the FB-111′ s range would have been increased by about 1,200 nm by this modification and that the aircraft’s total payload would have been increased to 15 nuclear weapons.

Interest for the aircraft developed again in 1980 with the Long Range Combat Aircraft (LRCA) studies. FBl-111A and F-111D aircraft were examined for conversion to an FB-11lB/C version. Again, the fuselage was to be lengthened to allow fuel, payload, electronics, and engine thrust enhancement. This proposal was dropped when the Air Force chose a modified B-l for the LRCA over the FB-111B/C design. But it should be pointed out that even with these improvements, the FB-111 could not match the range or payload of the long-range B-52 or the B-1.

The Australian government ordered 24 F-111C aircraft in 1963 to replace the RAAF’s English Electric Canberra. The British government ordered 50 F-111K aircraft in 1967. The F-111K was based on the F-111A, modified for British equipment and weapons. This included weapons bay changes, compatibility with the Martel anti-shipping missile, and the addition of a retractable refueling probe and the use of FB-111A landing gear for a higher gross take off weight. Prototypes of both the strike and TF-111K trainer aircraft were started and were in the final stages of build when the order was cancelled just over a year later. Updated estimates of performance indicated that range and speed at altitude would be worse than expected and fall short of the specification. Cost increase together with devaluation of the pound meant that the cost would be around £3 million each and this was the reason cited for cancellation.

In a nutshell, The F-111 was in service with the USAF from 1967 through 1998. It entered active service with the Royal Australian Air Force in 1973 and is currently scheduled to remain with the RAAF until 2010.

F-111F Technical Specifications

Crew2 (pilot and weapons system operator)
Length73 ft 6 in (22.4 m)
WingspanSpread: 63 ft (19.2 m), Swept: 32 ft (9.75 m)
Height17.13 ft (5.22 m)
Wing areaSpread: 657.4 ft² (61.07 m²), Swept: 525 ft² (48.77 m²)
AirfoilNACA 64-210.68 root, NACA 64-209.80 tip
Empty weight47,200 lb (21,400 kg)
Loaded weight82,800 lb (37,600 kg)
Max takeoff weight100,000 lb (45,300 kg)
Powerplant2× Pratt & Whitney TF30-P-100 turbofans - Dry thrust: 17,900 lbf (79.6 kN) each, Thrust with afterburner: 25,100 lbf (112 kN) each
Zero-lift drag coefficient0.0186
Drag area9.36 ft² (0.87 m²)
Aspect ratiospread: 7.56, swept: 1.95
Performance
Maximum speedMach 2.5 (1,650 mph, 2,655 km/h)
Combat radius1,330 mi (1,160 nmi, 2,140 km)
Ferry range4,200 mi (3,700 nmi, 6,760 km)
Service ceiling66,000 ft (20,100 m)
Rate of climb25,890 ft/min (131.5 m/s)
Wing loadingSpread: 126.0 lb/ft² (615.2 kg/m²), Swept: 158 lb/ft² (771 kg/m²)
Thrust/weight0.61
Lift-to-drag ratio15.8
Armament
Guns1× M61 Vulcan 20 mm (0.787 in) gatling cannon (seldom fitted)
Hardpoints9 in total (8× under-wing, 1× under-fuselage between engines)
Armament capacity31,500 lb (14,300 kg) ordnance mounted externally on hardpoints and internally in fuselage weapons bay

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