Capability trumps controversy

Yet during the 1960s and 1970s, the terms ‘F-111’ and ‘controversial’ were synonymous. Indeed, the aircraft was politically contentious even before it flew.

The US Air Force initiated a program for a new strike fighter in 1960. At about the same time, the US Navy identified a requirement for a fleet air defence fighter. In 1961, US Secretary of Defense Robert McNamara – a former corporate ‘efficiency’ guru – ordered the development of a single type to meet both requirements. Neither service liked McNamara’s ‘one-size-fits-all’ approach.

More angst was caused when McNamara over-ruled the recommendation of an independent panel that Boeing should be the prime contractor, instead awarding the job to General Dynamics. The Navy continued to fight the single-type concept, and eventually its model was cancelled. A British order was also cancelled, leaving the USAF and the RAAF as the only operators.

General Dynamics built some 550 F-111s at its mile-long factory in Fort Worth, Texas where raw metal went in one end and aircraft came out the other. The RAAF’s model was unique and was known as the F-111C. It was based on the F-111A built for the USAF, but had longer wings and a stronger undercarriage, which in combination allowed a higher all-up weight and slightly better range.

The F-111 pioneered many features. It was the first strike fighter with swing wings, afterburning turbofan engines, a crew capsule instead of ejection seats, and a fully automatic terrain following radar (TFR) system.

A number of USAF aircraft were lost in the early years, with several fatal crashes being caused by the failure of the wing carry-through box, the structural component on which the variable-geometry wings pivoted. RAAF crews had been training on USAF F-111As since 1967 but the accidents led to a political decision not to accept our aircraft at that stage. After much procrastination and some modifications, notably to the wing carry-through box, Australia’s first F-111Cs arrived at RAAF Amberley in mid-1973.

In order to meet the low-level, high-speed strike requirement, the F-111 had a very high wing loading, resulting in a Cadillac-smooth ride up to supersonic speeds. (By comparison, the F-4, with a much lower wing loading, was very rough at low level, such that at speeds above 450kt it was difficult to read the instrument panel. ) The down-side for the F-111 was poor turning performance; furthermore, at maximum all-up weight it had difficulty climbing above 15,000ft unless supersonic.

The other noteworthy comparison with the F-4 was drag. At any speed over 420kt, rapidly closing the throttles on the F-4 resulted in the crew being thrown forward against their ejection seat harnesses. The F-111, on the other hand, had such a smooth aerodynamic profile that in the standard cruise wing-sweep setting of 45 to 55 degrees, it would decelerate gracefully. However, moving the wings forward to 16 degrees of sweep produced more deceleration than deploying the speed brake. The maximum rear wing-sweep of 72. 5 degrees tended to be used only for high supersonic (Mach 2. 2) flight, or photographic work.

All F-111s were fitted with Pratt & Whitney TF30 afterburning turbofan engines. The TF30 generated increasing power all the way to maximum velocity: indeed, the limiting factor on the F-111’s top speed was not engine power but aircraft skin temperature. On the debit side, the TF30 was prone to stalling and required gentle handling during manoeuvres.

Automatic TFR operations could be interesting. The normal profile for auto-TFR was 540kt at 400ft above ground level, at night and in all weather. During operations in remote hilly regions, farmhouses appeared to have been built on stilts because their lights were well above the aircraft. A standard attack profile consisted of an auto-TFR entry to the target, a toss manoeuvre to deliver the weapons, and a dive back for an auto-TFR exit.

The aircraft were delivered with analogue navigation, radar, and visual bombing systems, and a visual gunsight. Over the course of 37 years, modifications included the addition of photographic and infrared reconnaissance packs, a Pavetack infrared targeting system, digital avionics, precision guided bombs, and anti-ship missiles.

Once the USAF retired its fleet the RAAF became the sole operator, and maintenance costs became unsustainable; moreover, the widespread introduction of ‘look-down shoot-down’ radar made the F-111’s low-altitude attack profile operationally untenable. By 2010 the aircraft had reached its use-by date.

The RAAFs F-111Cs never fired a shot in anger. But for almost four decades the aircraft provided Australia with a peerless deterrence capability.

Neither service liked McNamara’s ‘one-size-fits-all’ approach.