THE TRUE STORY OF THE GENERAL DYNAMICS F-111, A MUCH MALIGNED AIRCRAFT THAT WENT ON TO BECOME THE FINEST DEEP PENETRATION STRIKE AIRCRAFT IN THE WESTERN INVENTORY.

The F-111 must take credit for being the most misunderstood combat aircraft of the latter half of this century. Conceived as a nuclear strike aircraft, it was used very successfully in combat as a conventional bomber. It was meant to fulfil a wide range of missions, some as diverse as air superiority and naval air defence, yet it was optimised by design to air-to-ground precision strike. It was this fundamental conflict between the aircraft's nominal role definition and actual design which has provided feed for two generations of critics, none of whom as it seems ever took the time to understand the aircraft in the first place.

The Tactical Fighter Experimental or TFX was conceived in the very late fifties, the child of the USAF Tactical Air Command (TAC). TAC is the arm of the USAF which is tasked with providing air support for United States ground forces; as such it is responsible for the roles of air superiority, close air support and interdiction. The three primary roles have however assumed varied priorities over the years, and in 1958 the uppermost of these was interdiction, employing tactical nuclear weapons. There were several reasons for that stance, both the doctrine of the day and internal USAF rivalry coming into play.

Massive Retaliation as a doctrine suggested large scale nuclear strikes in response to any level of aggression; as a consequence of this policy the USAF Strategic Air Command (SAC) grew at the expense of TAC. TAC had little choice than to join in, and thus it prioritised its role structure to get as much out of the budget as possible. Its frontline fighter aircraft, the Republic F-105 Thud was a product of this philosophy. It was big, heavy, soft, fast at low level and armed with nuclear weapons carried within an internal weapons bay. Constrained to long smooth runways, its viability in its primary mission was very seriously threatened when ballistic missiles entered the scene in the late fifties. TAC could see SAC winning again, and thus it formulated the specifications for its next fighter, what was to become TFX.

The specs were formidable - unrefuelled trans-Atlantic deployment operation from unprepared dispersed strips, 2.5 M at altitude and high subsonic speed at sea level. Primary armament was to be a nuclear device, carried internally, on a Lo-Lo-Hi mission profile. This profile demanded an 800 nm strike radius, a sea level approach, followed by a 200 nm high speed subsonic dash to the target, weapon delivery and a medium altitude high subsonic return from the target area. The overall performance package was conceived as a growth upon the capabilities of the F-105; it was formally released under the July 1960 Specific Operational Requirement (SOR) -183. SOR-183 differed from the original spec only in demanding a supersonic, 1.2 M dash speed over the 200 nm low level run in.

Though NASA cautioned the USAF over this speed increase, suggesting growth in weight and size at the expense of payload/range, the USAF pressed on.

Other developments were also under way which would ultimately affect the program's development. The US Navy cancelled its subsonic F-6D Missileer aircraft, a dedicated air defence missile platform, and above all the Kennedy Administration came into office. The new Defence Secretary, McNamara, was to bring sweeping changes into US strategic and tactical doctrine.

Flexible Response, characterised by incrementally increased levels of military response, replaced the rigid concept of an all out nuclear shoot-out.

To support this new doctrine McNamara intended to build up a significant conventional strike capability, radically reversing the trends in TAC development. The F-105 was modified to carry iron bombs in preference to nukes, then it was subsequently cancelled in favour of the F-4C Phantom. He felt that both of these measures were inadequate and saw the TFX as conceptually ideal for his TAC doctrine. TFX was to become a multi-purpose tactical fighter, performing TAC's various missions and filling the role of the Navy's Missileer. It was assumed subject to fifties design philosophy, that high speed would ensure excellent air superiority performance. SOR-183 was thus modified. The original specs were not altered, but further constraints were added. 60,000 lb gross weight (2000 lb stores + fuel) for the USAF version, with a 10,000 lb conventional payload (with no payload/range spec!) and 55,000 lb for the Navy version, capable of 3.5 hr CAP 150 nm from a carrier with six 1000 lb missiles.

Both services objected strongly to the idea of joint development and both sought ways of keeping their original aircraft intact. The USAF convinced McNamara that an unmodified nuclear strike TFX would perform conventional strike superbly, anticipating his political demise at the next election and thus abandoning of the Flexible Response doctrine. The Navy saw a nuclear strike aircraft as unsuitable, aside from its traditional revulsion toward anything associated with the USAF Having failed with their attempts to stop the program or alter the specs, TFX went ahead. The USAF was nominated lead service, responsible for airframe development, the Navy was subordinate with responsibility for propulsion development.

Of the various submitted designs, only those of Boeing and General Dynamics were pursued. Both the USAF and USN favoured aspects of the Boeing design, which catered more closely for the individual needs of each service at the expense of commonality.

McNamara selected the GD design, the Navy version differing from the TAC version principally in 'bolt on' features. The configuration was optimised for nuclear strike, though GD promised only a 135 nm supersonic dash.

This was to have significant implications at a later date, when both the USAF and USN were to find that capabilities such as air superiority, perceived as a secondary role for both versions, really required specs other than high speed. At this stage the F-111 was frozen into the mould of a nuclear bomber with conventional capability and the unique requirements of this mission dominated the design of the aircraft. We must also note that the basic (and also unrealistically demanding) specifications for the aircraft required advances in the state-of-the-art in both aerodynamics and propulsion.

Full scale development was initiated in December, 1962.

F-111A - The Development Phase

Design work proceeded through 1963, a detail mockup being unveiled in August that year. Shortly after that, component manufacture was started employing however, hard production jigs. The first prototype was rolled out on October 15th, 1964. It flew in December that year; though the swing wing performed well the aircraft ran into difficulties elsewhere. These were no more significant than the bugs in any other design of the period, but were dealt with in a clumsy fashion which attracted the attention of the opposition in the legislative system and of the media.

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December 1964, and most of the current generation of F-111 aircrew are still in primary school as prototype No 1 undergoes its first flight. (General Dynamics)

This was the beginning of a campaign which succeeded in destroying the F-111's reputation before it even had a chance to prove itself. The greatest bug was in the development/ production schedule itself, which allowed virtually no time to introduce any design changes prior to full scale production. In the simplest of terms a development design was pressed into production before bugs were even identified.

The Navy contributed to this substantially, as we will come to observe. The aircraft itself was innovative - the first use of variable geometry, the first use of afterburning turbofans, the first use of an integrated nav/attack system, the first ejecting crew module and the first side-by-side seated cockpit in a high performance aircraft. Most of the development problems were rectified before affecting production substantially, the biggest problem being excess back end drag which was unfortunately never ironed out. Most attention was brought to the engine stall problem which was eventually solved.

The engine stall problem developed as a result of poor co-ordination between the engine and airframe manufacturers (and their respective supervising services). Initially, the engine manufacturer, Pratt & Whitney, had provided GD with a set of desired engine inlet parameters, to be met by the inlet to match the engine.

These were however, derived from turbojet characteristics, as no data on turbofans existed at the time. GD observed this spec while designing the inlet, which was specially chosen for minimum drag in a low level dash. It was recognised that the inlet may misbehave at high angles of attack (AOA), but the primary mission was supersonic low level dash and thus a draggier but less sensitive inlet geometry (chosen by the Russians on the F-111-like Fencer) was rejected.

The resulting geometry was sensitive to the turbulent airflow developed by wing glove/fuselage interaction at high AOA, but it wasn't regarded seriously by the turbojet experienced designers. The PW TF30 engine quickly demonstrated its sensitivity to the inlet, with repeated compressor stalls at Mach 2+ level flight or supersonic manoeuvring flight. The TF30 was inherently sensitive to turbulence near the compressor hub and really required further design work. P & W however, felt that GD were responsible, having designed the inlet incorrectly, but GD were adamant that the TF30 was to blame as the inlet met its specifications.

Both parties, having met their legal obligations, felt little need to solve the problem, which although having limited effect on the aircraft's mission performance, did impose flight restrictions. It is interesting to note that the issue was simply ignored in DoD memos, though it was known of since early 1965. The USAF subsequently applied pressure to both parties to resolve the matter. The TF30 compressor was improved and the inlet was reconfigured, the main modification being the curving of the inlet splitter plate. This inlet geometry moved the stalls out to Mach 2.35 in level flight or Mach 2+ in manoeuvring, thus no longer really affecting the basic mission profile. The revised geometry was used on all F-111A/C aircraft produced.

The USAF continued working on the matter, its System Program Office subsequently developing a stall free design. This employed an inlet with 10% more area, moved outward and without the splitter plate. This geometry was used by all subsequent versions, starting with the E. The inlet was however, draggier and reduced dash range to some degree.

The handling of the inlet/stall problem was characteristic of the whole program; the aircraft was committed to production in 1965 before the matter was even completely investigated, providing plenty of ammunition for the program's opponents.

Another bug which did little for the F-111's reputation was a fatigue crack problem associated with the high strength D6AC steel generously used in the structure. The cracking was not discovered until 1968 because the USAF simply followed its usual practices in fatigue testing (why rush?), but the F-111 flew a new type of mission profile and used new materials.

The result was a $100 million wing box retrofit program and lots of negative publicity due to crashes (this bug was probably the most often quoted 'deficiency' in the aircraft, even though it was rectified).

The only major area in which the F-111/TF30 as a system failed to meet its specification was the area of drag. Due to a lack of experience, the TF30 was designed with an exhaust nozzle geometry which creates substantial amounts of excess drag.

Apparently this is due to the flow characteristics of the bypass air, which differ from those of a turbojet. This was identified as a problem area in 1964 but inadequate funding of NASA research work resulted in an insufficient database for remedial action. The design was frozen before measures could be taken, thus the combined TF30 nozzle/airframe back end drag accounts for 30% to 40% of the F-111's total drag. Ideally it would account for about 5%. This is the only real problem the F-111 had, as it cut the ferry range and dash range.

By the end of development the aircraft met most of the primary performance specifications set out, though it did fall short in areas deemed to be secondary by TAC. The following table illustrates the emphasis placed upon specific areas, during design.

TFX F-111A Specification Performance Maximum speed - SL1.2 Mach 1.2 Mach - at altitude 2.5 Mach 2.2 Mach Cruise speed (at altitude) 2.2 Mach 2.2 Mach Combat radius 800 nm 800 nm (540 nm) Dash radius 210 nm 30 nm (200 nm) Ferry range 4180 nm 2750 nm Maximum payload 10,000 lb >25,000 lb Ceiling 62,300 ft 58,000 ft Acceleration (0.9 to 2.2 Mach) 1.45 min 4.0 min Take off weight 69,100 lb 82,500 lb

As is very apparent, the aircraft met the specified penetration speed and exceeded the conventional payload spec. The dash radius was the only area the USAF was unhappy with, but accepted it, perhaps realising how far-fetched the original specification was.

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USAF F-111s have been frequent visitors to Australia over the years, primarily in support of the Kangaroo series of exercises. The large undercarriage main gear and various high lift devices are clearly evident in this photo. (DPR)

The aircraft entered service in October 1967, with the 474th Tactical Fighter Wing. A series of evaluations were then carried out, Combat Bullseye, Harvest Reaper, Combat Trident followed by the March/April 1968 Combat Lancer trials in an effective demonstration in combat. Unfortunately neither the aircraft nor crews were ready, and the result was the loss of three of six aircraft in a matter of weeks. The F-111A wing had not even attained initial operational capability (IOC) when the deployment was ordered and the aircraft was pressed into its secondary role of dropping iron bombs. A very likely reason for some of these losses was incorrect energy management in terrain following, when fully loaded the aircraft would be unforgiving of errors due to the thrust limitations of the early TF30P-3.

Vietnam had a profound effect on TAC and its philosophy of weapon design. TAC found itself fighting a dumb bomb war with expensive aircraft such as the F-105D ill suited to the mission, inherently soft and not very manoeuvrable, the Thuds were decimated by AAA and some even fell victim to subsonic MiG-17s.

F-4 Phantoms had to fly MiGCAP covering the Thuds, but even the F-4 ran into difficulties with the supersonic MiG-21s, the USAF suffering an unfavourable exchange rate with the 21s at one stage. Vietnam exposed the defective reasoning that suggested high speed and air-air missiles as the means to air superiority. It was suddenly recognised that thrust-to-weight ratio and energy bleed, coupled with close-in weapons capability, were more important factors.

Similarly dropping iron bombs required as much thrust as available, for payload/range and agility when loaded. In that sense, TAC began to question the role definition of the F-111A. Air superiority was ruled out and the conventional strike role was more tightly constrained, to take advantage of the aircraft's qualities rather than force it into ill suited payload configurations. The TF30P-3 was acceptable for conventional bombing but imposed some limitations upon both acceleration and payload/ range when the aircraft was heavily loaded with draggy iron bombs. The thrust/weight limitations of the A-model were not regarded seriously, the aircraft had superior payload/range to any other tactical aircraft in the inventory. It was only much later that the F-111F was equipped with more powerful engines.

F-111A - The 1972/73 Combat Deployment

1972 was the year of the Spring Offensive and the F-111A returned to the South East Asian theatre with a vengeance, that September, playing a significant role in the later Linebacker II bombing campaign.

Forty eight aircraft deployed to RTAB Thakli, in Thailand; the first missions were flown within hours of arrival. The aircraft were tasked with hitting some of the most heavily defended targets in North Vietnam. Though the 474th TFW was kept busy throughout the deployment, it was put to test in December, the sortie rate shooting up with the commencement of Linebacker II.

Over 30 missions were flown each night, a third usually dedicated to defence suppression - the F-111As busting SAM sites and radar/command/ communication facilities 30 minutes prior to a scheduled B-52 strike on the target area.

By the end of hostilities the 474th TFW had chalked up well over 4000 missions, dropping 74,000 bombs, mainly 500 lb but also 2000 lb and cluster munitions. Eight aircraft were lost (seven crews), mainly in the initial phases of the deployment, resulting in an overall loss rate of 0.2%. A typical mission would involve a low level high subsonic run in with a payload of twelve 500 lb bombs, the whole mission lasting 2.5 hours and flown in pitch black darkness. Significantly all missions were flown without the support of tankers, ECM platforms, Wild Weasel SAM suppression aircraft and fighter cover. Each F-111A could carry twice the payload of an F-4 Phantom over 2.5 times the range and the USAF acknowledged the aircraft as being the most cost effective employed throughout the conflict.

F-111A Derivatives - F-111C, K & E

Only 141 F-111As were produced, the F-111E with its Triple Plow II inlet superseding the A in production. Both aircraft were equipped with a fully analogue nav/attack system (see article on F-111C) and really differ only in the inlet. Ninety four F111Es were eventually produced, the remaining aircraft now equipping the 20th TFW USAFE, based at Upper Heyford in the United Kingdom.

The RAAF's F-111C is also derived from the F-111A, differing in wingspan, undercarriage and a series of internal changes. As a result of adverse publicity spilling over from the US, the RAAF had come under severe criticism for choosing the F-111. The RAAF ordered 24 aircraft in 1963, anticipating delivery in 1968. The various development problems precluded delivery, all aircraft remaining in the US until modifications were carried out. The aircraft were delivered in 1973, after their unit cost grew from several million dollars to $24 million apiece. If the RAAF is to be criticised over the matter, it should be only over initial contractual arrangements with the US. The choice of the aircraft was appropriate for the mission, the only reasonably suitable alternative (F-15E) to the aircraft won't be available until 1985+. The aircraft provided an excellent long range strike and photo reconnaissance capability and with an upgrade could be employed as a nuclear strike force.

The last member of the F-111A family was the F-111K, a version to be used by the RAF in preference to the TSR 2. Fifty aircraft were ordered, but even this figure was too much for the political scene of the day and the order was cancelled in 1968, in favour of an inferior version of the F-4. The RAF had to wait until the early eighties for the Tornado GR.1 to fill the resulting gap in strike capability, the Tornado is substantially smaller and lesser in capability.

With an unrefuelled range of over 2000 nautical miles, the EF-111A tactical jammer will provide an invaluable aid to the support of strike forces in any future European conflict. Aircraft is basically a heavily modified A model with more than four tonnes of specialised electronics dedicated to the jamming and information gathering role. (Grumman)

In perspective the F-111A/E/C family has proven itself as operationally highly effective, even if employed in a role secondary to that which it was designed for. The aircraft provided its users with an entirely new range of capabilities, it is only unfortunate that the development program was so badly mismanaged as to deny the aircraft the full performance range it was capable of. Most of the criticism directed at the aircraft was done so unjustly, generally by parties who wouldn't know an oleo from an elevon. Even so the fate of the F-111A was far better than that of its ill-conceived relative, the F-111B.

General Dynamics / Grumman F-111B

The US Navy was unhappy with the idea of using a USAF aircraft, whatever the mission may have been. The fleet defence fighter role basically demanded an aircraft with good loiter capability (recall mods to SOR-183) and the prospect of using a design optimised for low level strike, at the inevitable expense of other qualities the Navy desired, was felt to be unacceptable throughout the service.

The Navy sought a way out of TFX; in a seemingly unconnected move it sought a proposal for VAX, a new strike aircraft. VAX was a swing wing, supersonic at altitude, subsonic at sea level strike aircraft, one half the size and weight of TFX (the Boeing VAX proposal apparently resembled the Boeing TFX closely enough to be dubbed F-55.5!).

McNamara easily identified the Navy's ploy, the eventual use of VAX instead of the Navy TFX (VAX totally contradicted USN doctrine on strike aircraft), and he promptly cancelled the program. The Navy seemingly accepted defeat, but initiated a series of measures which had a decisive effect on the performance of the Navy TFX.

The core of the USN's argument against the use of TFX was its excessive weight, a consequence of TAC's performance specs.

The USN however, rigorously applied Milspec reliability constraints to the design, forcing weight up by at least 1000 lb. The Navy refused the substitution of the crew capsule with ejection seats, which would have saved 500 lb, the reduction of the 3.5 hour loiter time and would not consider reducing the Phoenix missile (1000 lb each) load from six to four.

It is interesting however, to note that the later F-14's specs were set with six 500 lb missiles. The allowable g-loading with full missile load was not relaxed (which it was with the F-14) and the demand for two 1000 lb missiles in the internal bay was maintained.

The Navy specified a large volume for the AN/AWG-9 fire control system, weighing 1900 lb (the AWG-9 was shrunken in size and reduced in weight to 1300 lb, for the F-14 airframe).

All of this occurred as Grumman went through the pains of a Super Weight Improvement Program (SWIP), often to the point of scraping ounces of metal off some components. SWIP was followed by the Colossal Weight Improvement Programs I, II and III. As a result, the weight was stabilised in the region of 43,000 lbs.

The Navy still wasn't satisfied; it felt that the combined weight/speed of the F-111 would be at the limits of what the flight deck arresting gear could handle. A reduction in approach speed of 15 kts was specified, to be achieved by increasing wing lift. The result of this was the necessity to run the aircraft's engines close to idle in approach, not to pick up excess speed. That in turn created complications, as carrier recoveries demand that the aircraft's engines respond quickly, to allow the pilot to safely pull away if he fails to trap an arrestor cable (note that A-6 bombers recover with speed brakes deployed, engines well above idle, for this reason alone). It was therefore necessary to run the engines at higher thrust settings, while increasing the aircraft's drag not to increase speed. Grumman added to the spoilers and increased the drag, achieving the desired result. As a side effect, however, the angle of attack in approach changed, the aircraft then having a more nose-up attitude which spoiled the view out of the crew module.

To add to this, the USN adopted a very specific policy in their choice of test pilots. The Missileer was to have been flown by bomber crews, however the F-111B was flown by ex-fighter crews, mainly from F-4 Phantom squadrons.

One of the characteristics of a turbofan, compared to a turbojet, is its far lower dry thrust output (though more fuel efficient) for comparable afterburning thrust levels. To the F-4 pilots, the F-111B felt terribly underpowered in dry thrust and hardly acceptable in afterburner; the difference in specified mission was disregarded where possible.

The very real high AOA inlet problems inherited from the TAC airframe added nothing to the Navy pilots' lack of enthusiasm.

The DoD decided to press the USN for some set of specs which would make the F-111B into an acceptable aircraft. These were termed the N-1 package, involving raising the crew seats, changing the windscreen, flaps, fuselage length and forward undercarriage position. Fuel capacity was increased by 2000 lb to meet the loiter spec. Throughout this procedure, heated political debate went on as to the actual viability of the F-111B. The Navy's strategy was beginning to pay off, as the F-111B acquired a dismal reputation (although only partly deserved).

The Navy now required an excuse to kill the aircraft, having created the desired political climate. Concurrently, the Navy was considering its next air superiority fighter, having found that the Phantom, though acceptable in Vietnam, would be up against far tougher competition in the newer Russian Flogger and Foxbat.

VFAX was conceived as a combined air superiority and strike fighter, however it was then that the Navy perceived a fatal threat - the USAF initiated development of the FX (F-15 Eagle) which bore a lot of resemblance to VFAX. As one may guess, joint development was again in the air, and the USN was hardly in the frame of mind to accept it.

Only given that the Navy had no aircraft to carry the Phoenix system, desperately needed, could it justify the development of a new fighter with little similarity to FX and thus a pure Navy design. The F-111B, though finally a workable design, was doomed, being the victim of both political factors and its narrowly defined mission and capabilities. The F-111B was terminated on July 10, 1968, after the Navy deliberately slowed development tests.

Funding was transferred to the newly initiated VFX program. VFX became the F-14A, a substantially better aircraft than the F-111B, if only by virtue of a far more realistically defined mission. VFAX was later re-initiated and became the F/A-18A.

The history of the F-111B is testimony to the futility of political meddling in weapon system development and structuring of defensive strategies.

F-111D

The digital F-111D was developed as a TAC version with an enhanced conventional capability over the analogue A/E family.

It was the product of studies by the Director of Defense Research & Engineering (DDR&E) and was strongly opposed by the USAF. DDR&E was previously involved in ballistic missiles, and as such conceived an enhancement to the F-111 based upon improved avionics. The rationale was simple: increase the accuracy, thus reducing the number of necessary missions = force multiplication.

The idea was easily sold to McNamara who wished to see the F-111 with as much conventional capability as possible; he lacked the judgement to see the fallacy in the DDR&E's arguments. The aircraft has essentially the same airframe as the E-model, but is equipped with the 20,800 Ib TF30-P-9 engine, a bootstrap cycle environmental control system and the uprated undercarriage of the FB-111A.

The big difference is in the upgraded digital avionic system, designated the Mk II Avionics Package. The original APQ-113 attack radar was replaced with the APQ-130, lookdown capable and equipped with an illuminator to support the AIM-7G Sparrow missile.

The APQ-130 has improved air-ground performance including Moving Target Indication (MTI), and will also target later models of the AIM-9. The terrain following radar was replaced with the upgraded APQ-128 (as used by the RAAF) and the original RHAWS was replaced with the later APS-109C model, just as the Countermeasures Receiver was upgraded to the ALR-41. The nav-attack underwent even more radical changes, the AJQ-20 being replaced by the AJN-16, enhanced by integration with an AYK-6 digital computer and APN-189 Doppler nav system.

This arrangement provided more accuracy and the flexibility of software configuration. The cockpit was radically resculptured to accept the AYN-3 Horizontal Situation Display and AVA-9 Integrated Display Set. This resulted in both crew members receiving HUDs, the pilot a rectangular CRT display, larger TFR scope and the navigator a very large rectangular radar display. The HSD will display position and flightpath parameters superimposed over maps or recce photos.

The avionic system was a first generation digital design, developed by Rockwell Autonetics, though the integrated display set was built by Norden. The package was very expensive, delayed well behind schedule and initially unreliable, the display set apparently requiring substantial changes. Though the prototype first flew in late 1968, the absence of an avionic system delayed development considerably. As the bugs were eliminated from the Mk II avionics, they became also more expensive. The cost increase was sufficient to cut production from 315 aircraft down to 96, and totally cancel the standing order for 60 RF-111Ds with fuselage recce pallets.

IOC was achieved in late 1972; the aircraft are solely operated by the 27th TFW USAF It is worth noting that the loss of availability due to reduced reliability easily counteracts any force multiplication effects. The reliability and cost problems of the Mk II avionic system led to further development, as the USAF wanted more F-111s but could not accept higher costs.

F-111F

The F-111F was the only version truly optimised for the conventional air-ground strike role. The aircraft had uprated TF30-P-100 engines, delivering 25,100 lb in reheat, some structural changes and a radically revised avionic system. The Mk II avionics were replaced by the far cheaper (by 50%) MK IIB package. The attack radar was again changed (the Doppler tracking filters removed, eliminating MTI and A/A declutter), to the APQ-144, the TFR to the APQ-146 and the cockpit was revised. The original A/E layout was adopted, including the stores control system and original radar panel. An uprated Head-up Sight, the ASG-27, replaced the dual HUDs of the D-model. The digital computer and inertial bombing and nav system were retained, the Doppler system was dropped with a 9% loss in bombing accuracy.

The F-111F is the best performer among the F-111s, be it in flight performance or reliability.

The USAF had intended to purchase 219 aircraft, but this was cut down so that despite the USAF's efforts, only 106 were ever built.

The aircraft achieved IOC in late 1972, with the 347th TFW. They are now operated by the 48th TFW USAFE stationed at Lakenheath, UK.

Though the F-111 was the TAC's bird, it did not go unnoticed by the Strategic Air Command, who desperately needed a bomber to fill in before the B-1A could assume the roles of the B-52 and B-58 Hustler. Thus the FB-111A came into being.

FB-111A

The SAC FB-111A is a dedicated nuclear strike aircraft, with a secondary conventional strike capability. The fuselage was stretched by two feet, increasing fuel capacity by 590 gal, the undercarriage was strengthened and 20,400 lb TF30-P-7 engines installed. The wings were extended, as in the B and C models. The avionic system is extensive and unique to the SAC aircraft. The attack radar is the APQ-114, the TFR the APQ-134. The nav attack uses the AJN-16 and AYK-6 computer as in the D/F aircraft, but these are supplemented with an APN-185 Doppler nav set and an ASQ-119 astrocompass. The AYN-3 HSD of the D model is employed, together with an ASG-25 gunsight. The RHAWS and ECM are identical to TAC versions. Due to the nature of its mission, it has provisions for additional fuel and SRAM (nuclear) defence suppression missiles. The FB-111A may carry six 600 gal wing tanks, compared to four on the TAC versions.

Configured for nuclear strike, it can carry six nuclear weapons, either 843, B-57 or B-61 free fall devices, alternately AGM-69A SRAM missiles. Four weapons are carried on the inboard (pivot) wing stations, two in the weapons bay. The free fall devices may be dropped using any of the delivery techniques for conventional bombs, whereas the SRAM, inertially guided, must be initialised by the FB-111A's INS prior to launch.

The FB-111A achieved IOC in 1971, and has been in service ever since. It is currently anticipated that it will complement the B-1B LRCA well into the nineties. Though the USAF required 263 aircraft, this was cut to 126 and subsequently to 76, which was the final number produced.

The digital versions of the F-111 were the last to remain in production, the Carter administration then seeing to the shutdown of the line in 1977. This by no means reflects upon the aircraft's usefulness, as the USAF had initially intended to purchase 1706 aircraft, amending that later to 785 and finally receiving 533 units.

The demand for the F-111 is such that even the re-opening of the production line was apparently considered. In the short term, attrition losses were partially made up by the establishment of a dedicated restoration facility in Fort Worth. General Dynamics rebuild crash or fire damaged aircraft back to as-new status, including major structural rebuilding. The facility has restored about ten aircraft, to date, the USAF airlifting the damaged aircraft in with C-5s. The rebuilds cost up to and over $5 million, which is little compared to an estimated price per unit of $45 million for a new aircraft, given production were to resume. It is this shortage of aircraft that caused the RAAF great difficulties in acquiring four attrition F-111As; that problem will become far worse in the long term. The USAF will retain one wing operating each TAC version, the excess 40 F-111As being converted to EF-111A tac-jammers. In the long term, the USAF is adopting the F-15E Strike Eagle to supplement the F-111s, with a comparable avionic and payload/range capability.

EF-111A Raven

Aptly named, the EF-111A Raven continues in the footsteps of its TAC predecessors as the best in its class. Development of this sophisticated ECM platform began in 1973, the USAF having been thoroughly impressed with the performance of the USN Grumman EA-6B Prowler, which easily outclassed the USAF's geriatric EB-57 and EB-66 aircraft. Though these aircraft were adequate in Vietnam, they were obviously inadequate for the European theatre.

The USAF decided upon adapting the USN's ALQ-99 computerised tactical jamming system, as used in the EA-6B, but required a high performance platform with good endurance to carry the system. The F-111 was perfectly suited to the mission profile and was subsequently modified for the role. The task was challenging: adapt the F-111A to the ALQ-99 and modify the ALQ-99 for use in the EF-111A. The ALQ-99 in the EA-6B is operated by two dedicated ECM Officers and a Navigator/Communications jammer.

The EF-111A carries only a pilot and Electronic Welfare Officer, therefore the ALQ-99 had to be substantially modified for single operator use. The program was carried out by Grumman and Raytheon, the former chosen for integration experience with the EA-6B and an intimate knowledge of the F-111A/B, the latter as the builder of the ALQ-99.

Physically the EF-111A is noticeably different from the strike versions, with a large canoe shaped antenna fairing protruding from the weapons bay, and a large and bulbous antenna fairing on the top of the tail. The latter houses the ALQ-99 antennae and receive aerials for the ALQ-137 and ALR-62 RHAW. The AAR-34 IR scanner is retained. The weapons bay then contains an array of ten independent jammers, each controlled by the EWO from his right hand console. The wing gloves and nose contain further antennae belonging to the ALR-62 and ALQ-137. Electronically, the aircraft has all the attributes of a porcupine.

The TFR and countermeasures dispensers of the A-model were retained, together with the nav-attack, but the attack radar was changed to the APQ-160.

The cockpit was thoroughly redesigned, the nav-attack panel shifted to the centre beneath the TFR, radar and RHAW scopes. Most of the EWO's panel space is occupied by a large rectangular CRT display, used for jammer/jamee status data. Most of the starboard console is occupied with jammer/receiver control panels which replace the original radar and stores control panels.

The automated jamming system is awesome in its capability; some sources suggest one half dozen aircraft could entirely disrupt Soviet radar and communications along a front extending from Norway down to Italy. The aircraft will be operated in three primary modes. Standoff mode involves flight along the friendly side of a battlefront, jamming enemy radar blind to deny the enemy surveillance of friendly territory. With an on-station endurance of four hours, unrefuelled, the EF-111A may screen friendly aircraft from hostile radar also up to 40 nm deep into enemy territory.

Related to the stand-off mode, the close support mode involves short range electronic screening of friendly close support aircraft, in Europe USAF A-10As, as they attack hostile ground forces. The considerable density of Russian SAM /AAA systems coupled with the close in attack profile of the A-10 necessitate large amounts of jamming power to achieve reasonable levels of disruption. The most demanding role for the aircraft is however, Escort/countermeasures support, where the EF-111A will penetrate deep into enemy territory, screening strike aircraft from air defence radars.

The USAF are modifying 42 A-models to EF configuration, at a considerable cost (basic ALQ-99 well above US$50 million), the first production deliveries being made. in November 1981. The aircraft attained IOC in December, 1982, when the 390th Electronic Combat Squadron became operational. The aircraft has been deployed to Europe; the 42nd ECS of the 20th TFW is based at Upper Heyford supporting the two F-111E/F strike wings. The EF-111A is the latest, though possibly not last derivative of the F-111 family. Though the basic aircraft have changed little since entry into service, most have had their APS-109 RHAW systems replaced with the newer ALR-62. Support problems caused by the multitude of differing avionic fits have proved to be a real pain for the USAF That itself restricted the fit of the Pave Tack FLIR/laser pods to the digital F-version only and also led to repeated calls for a large scale refit to F-model status.

That never occurred; only now that the F-model avionic fit is itself becoming obsolete, moves are under way to update the whole fleet. The aircraft will receive new computers, radars, TFRs, Doppler nav sets, INSs and SRAM interface avionics. This would achieve commonality throughout the whole fleet, with an increase in accuracy, reliability and adaptability, the latter by virtue of the software programmability of the weapon/ nav systems.

Refitted with new avionics, the aircraft will last in front line service beyond 2000 when most will run out of their 10,000 hrs of airframe life.

The F-111 is currently regarded as the spearhead of NATO's strike force, the two USAFE wings in the UK providing NATO's only deep penetration strike capability. The introduction of the new F-15E dual role fighter was necessary, both to reduce the amount of battlefield interdiction imposed upon the F-111s, thus freeing them for their primary role, and to maintain an open strike fighter production line to rapidly respond to attrition in the event of a conflict. The aircraft are complementary in capabilities; though the F-15E is more the tactical fighter it can hardly replace the F-111 in the dedicated deep strike role.

The F-111 has a unique place in aviation history, a place characterised by extremes. Extremes in specified performance, combat capability and complexity, and of course the dubious distinction of being the most criticised combat aircraft of its generation. To be fair to the aircraft, we must note that virtually every problem it ever had stemmed from the immaturity of the advanced designs used, as its designers pushed the technology of the day to the limit.

That was further compounded by a misdirected and inflexible development policy, exacerbated by the Navy's attitude toward the F-111B.

The aircraft has been used in roles as diverse as jamming and reconnaissance, and it is furiously defended by its users on both sides of the Pacific. For an aircraft described as 'unsafe... defective ...a deathtrap' (quoting a Senator W. Proxmire, previously distinguished in the killing of the Boeing SST program) it seems to have built up a surprising record, bath in combat and in peacetime use. It is for the reader to judge the rationality of its critics.

The facts speak for themselves.