Fighters For The Missile Era
The Variable-sweep wing F-111
The General Dynamics F-111 was a controversial Air Force fighter-bomber, and only after years of service is it possible to understand the aircraft’s place in history. The most conspicuous feature was the variable-sweep wings enabling the big twin-engine two-seater to operate from smaller air bases while achieving Mach 1.2 at sea level and Mach 2.2 at altitude.
From a 16-degree sweep and 63-foot span at takeoff, the wings could be gradually swept back to a 72-degree sweep and 32-foot span. Two crewmen sat side-by-side in a pressurized compartment contained in an escape module that could be ejected at any speed and altitude. An inflight refueling boom receptacle was behind the cockpit.
While armament provisions included a 20-mm M61Al with 2,000 rounds and two AIM-9B Sidewinders, the
F-111A never engaged enemy fighters, but was a tactical bomber. The basic mission was delivery of a nuclear bomb (Mk 43 or 57) in the weapons bay, or four 2,000 or 12 750-pound bombs on four wing pylons. These pylons could also be used for 600-gallon ferry tanks or a variety of bombs or dispensers. Four more outboard pylons for smaller stores were seldom used.
But the F-111’s greatest virtue was the accuracy with which bombs could be delivered at night by the AJQ-20 inertial bombing-navigational system and the computerized APQ-113 attack radar. The first USAF aircraft with APQ-110 terrain-following radar was able to fly close to the ground, below the level of radar observation.
Development of the F-111 series was initially based on a July 1960 operational requirement for an all-weather fighter-bomber to replace the F-105 series, utilizing turbofan power plants and a variable-sweep wing. This concept, described as the TFX tactical fighter, was changed when the new Secretary of Defense, Robert S. McNamara, requested in February 1961 that the Air Force try to join
with the Navy to produce a common design. Such commonality did work with the F-4s and was an attractive way to control costs.
The Navy had planned a two-place straight-winged fighter with two Pratt & Whitney TF-30 turbofans, designated the Douglas F6D-1 Missileer. Ordered July 21, 1960, it would carry six large Eagle (AAM-N-10) long-range-missiles under the wings. This relatively slow 60,000-pound aircraft would loiter for up to ten hours until its radar spotted targets for the missiles’ own radar homing system. That program was cancelled April 25, 1961.
Instead, Secretary McNamara insisted on a common fighter design with the Air Force, proposing on September 1, 1961, a twin-engine, supersonic two-seater with accommodations for either 10,000 lbs. of bombs or six large air-to-air missiles, and weights and dimensions limited by Navy carrier requirements.
The Air Force also insisted on transatlantic ferry capability, with the ability to operate from unprepared fields, as part of its NATO support role. On September 29, new requests for proposals were sent to manufactures, and nine responded by December. The designation F-111, last of the old fighter series, was assigned to the program.
Boeing and General Dynamics each received design data contracts in February 1962, and submitted second, third and fourth proposals that year. Boeing’s design used a General Electric engine design (as yet untested) with intakes above the fuselage, and General Dynamics chose Pratt & Whitney TF30 turbofans, with intakes under the wings. The Air Force Selection Board preferred the Boeing design as promising better performance at a lower price, but the Secretary of Defense ordered the TFX contract given to General Dynamics, because of the higher degree of identical structure for the Air Force and Navy versions, and the belief that Boeing’s cost estimate was unrealistic.
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