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General Dynamics F-111 Ardvark

 

gdf111
F-111


During the 1950s, the general development of tactical aircraft moved in the direction of greater performance, at the expense of long field length, high cost and inflexibility. By 1959, USAF Tactical Air Command was ready to plan a new aircraft, in the first instance to replace the F-105, which would combine many new features and offer outstanding capability and versatility. In particular, it would be the first combat aircraft to have a variable-sweep (so-called 'swing wing') aerofoil to match the conflicting needs of high lift at takeoff or landing, low-speed efficiency in subsonic cruise or loiter, and minimum-area minimum-span shape for low-level attack at the highest possible speed.


What caused great difficulty was that, in the first place, the TAC planners set their sights too high in drafting Specific Operational Requirement 183, so that the figures could not be met. Second, the US Navy in 1959 also wanted an important new aircraft, a Fleet Air Defense Fighter, carrying a powerful radar and long-range missiles. In 1960, the new Secretary for Defense, Robert S McNarnara, studied the two requirements and, in his words, 'was struck by the high degree of similarity'. After discussion with his civilian aides, he decided to urge that the USAF and Navy work towards a common aircraft design. His advisors suggested that such a move, called 'commonality', would save a billion dollars.


After the longest and most hard-fought procurement battle in history, General Dynamics Fort Worth won over Boeing-Wichita, the choice being announced on November 24, 1962. There had been an unprecedented four rounds of detailed technical and cost bidding, and in each round the consensus of customer opinion had, it was claimed, favoured Boeing. The Wichita team had not only offered what was in some respects a superior product, but they had consistently quoted a lower price. After Pentagon adjustments, the quotation for research, development and production of a total of 1726 aircraft (231 of them to be of the navy version) by Boeing was $5387 million and that from GD was $5803 million. As soon as the decision was announced, there was a storm of protest in Washington. It grew, as there was a prolonged public enquiry, and the position was later exacerbated by trouble with the winning aircraft and consistent failure to meet the impossible specification.


GD flew the first F-111A on December 21, 1965, and on the second flight operated the wings through the whole range of sweep, from 16 degrees to 72.5 degrees, ahead of schedule. An attempt to win a further bonus by exceeding Mach 1 was thwarted by severe engine compressor stall. The chosen engine, the Pratt & Whitney JTF10A-20, later given the military designation TF30-P-1, had been selected because it was a typically conservative Pratt & Whitney product. It was likely to deliver the modest specified performance - maxi-mum thrust with full afterburner was only 8390 kg (18500 lb) - and give little trouble. It was the world's first afterburning turbofan, calculated to combine high performance in the supersonic dash mode with excellent fuel economy in the subsonic cruise regime. The new feature of afterburning in both the core and fan streams gave little difficulty, but the installed powerplant was a disaster. Part of the problem was that, to save weight, General Dynamics had cut the inlet ducts back under the wings, and turbulent air was hitting the aerodynamically tricky compressor. It took considerable redesign of the engine and a total redesign of the inlet system, with a so-called triple flow 3 inlet, before the installation would work properly in all flight regimes.


Further extremely severe trouble was met with aircraft weight and drag, so that at first the specified range was not even approached. During 1965-66, using 18 development aircraft, the Fort Worth team restored some of the lost range by increasing the internal fuel capacity. This naturally raised the gross weight sharply, and accentuated the already marginally acceptable large size and weight of the F-111B Navy fighter version, co-producer of which was Grumman. After years of toil the F-111B came to an end in 1968 simply by the refusal of Congress to vote any further funds.


This removed the captivating goal of commonality, leaving the F-111A not quite the way it would have been designed for the USAF alone. A further fundamental point is that, partly owing to confusion over the concept of a 'fighter', the F-111 had been planned to replace all the tactical aircraft of the USAF, including fighters, and attack bombers and fighters of the navy. In fact, the resulting aircraft was in no way a fighter, though with different radar and missiles it might have been a long-range intercepter. Though it had been given an internal gun, a 20-mm (0.79-in) M61 Vulcan, with its ammunition drum occupying the internal weapon bay instead of bombs, this gun had no air-combat role and was removed from most of the delivered aircraft. The F-111A was instead a bomber.


Though the internal bay had been included to carry two B61 nuclear bombs at supersonic speed in a low-level or high-altitude attack, the main weapon load has always been hung externally. There are eight hard points on the wings, and all are on the swinging part; there are no pylons on the fixed gloves or fuselage. The outer pylons are seldom fitted, and a normal weapon load is 24 bombs (eight triplets) of a nominal 226 kg (500 lb) on the four inners, a true weight of 6314 kg (13920 lb). The F-111A can also carry a wide range of cluster bombs, dispensers, ALQ-119V ECM pods and other stores.

 

 GD-F111-01

 

The F-111A was the first tactical aircraft to go into service with blind first-pass strike capability. The equipment needed includes a large multi-mode nose radar (in most versions, by General Electric), with two small dishes serving a terrain-following radar (TFR).


The right-seater is an observer or weapons-system officer, with comprehensive navigation and radar displays, and in the terrain-following mode it is his job to keep the pilot constantly informed about obstructions or other objects coming up ahead.


The F-111 crew sits side-by-side, both are enclosed in a capsule which separates from the aircraft in an emergency, a proven escape system which obviates the need for ejection seats.


In addition to 17 F-111As for development work, 141 went to the 4881 Tactical Fighter Squadron at Nellis AFB in July 1967, for intensive trials evaluation. With four tandem-triplets of bombs, the maximum speed proved to be about 925 km/h (575 mph) at typical attack height; with two bombs in the weapon bay and nothing exter-nal it was Mach 1.1, roughly according with SOR-183. At height the attainable speed in the clean condition was about Mach 2. Ferry range with six 2271-litre (500 Imperial gallons) drop tanks is about 6400 km (3980 miles). These were powered by two 8392kg afterburning thrust Pratt & Whitney TF30-P-3 turbofans. In March 1968, six F-111As of the wing's 428th Tactical Fighter Squadron under Colonel Ivan H. Dethman were rushed to Takhli, Thailand, to begin combat operations against North Vietnam. The first three aircraft launched on the first three missions vanished for ever, although the detachment later flew 55 missions successfully. The USAF discovered, as a prisoner of war from this deployment would later confirm, that a tailplane problem caused uncontrollable pitch-up and roll. A separate fatique problem caused wing spar cracks and, in 1969, resulted in the loss of an F-111A when its wing was torn off. In 1969, the entire fleet of 300 aircraft was grounded while an exhaustive structural review programme remedied these problems.


GD delivered 141 of the A-model with TF30-3 engines, including two YF-111A air-craft rebuilt from a cancelled British order for 50 F-111K.


The Strategic Air Command's FB-111A, operating with two wings, is a very long-range variant powered by two 9230kg afterburning thrust Pratt & Whitney TF30-P-7 turbofans, with modified inlets, long-span wing, and provision for nuclear or thermonuclear weapons or up to 50 340kg HE bombs; 76 FB-111As were built.


The Royal Australian Air Force bought 24 F-111C with long-span wings and stronger landing gears, these suffering a nine-year delay due to structural problems and contract uncertainties and were delivered to Australia in 1973 after lengthy delays. The F-111C differs from the F-111A model in having a longer-span wing and stronger landing gear. Four F-111Cs have been converted to the reconnaissance role and the remainder, like many USAF 'Aardvarks', are being equipped with Pave Tack pods for laser acquisition of ground targets.


The Royal Australian Air Force operates three versions of the F-111:
- the F-111C strike fighter
- the unique RF-111C, modified for photo-reconnaissance work, and
- ex-US Air Force F-111G's, which help ensure Australia maintains its strike capability until the F-111 is retired.

 

GD-F111-Aust
RAAF F-111s January 1989

 

The F-111D, F-111E and F-111F are variants of what has become a highly specialised long-range strike aircraft ideal as a counter to the Soviet Sukhoi Su-24 and as a means of hitting targets in eastern Europe from the British Isles. These variants are located respectively at Cannon AFB, New Mexico, RAF Upper Heyford and RAF Lakenheath, England. Production amounted to 96 F-111D, 94 F-111Es and 106 F-111Fs.


The F-111H was a proposed strategic bomber once perceived as an ideal interim step for the 1980s when it appeared that the Rockwell B-1 had been cancelled. The F-111K was the intended version for the UK's Royal Air Force. Neither was built, and total production amounted to 562 airplanes.

The F-111D, of which 96 were built, has the slightly more powerful 8891-kg (19600-lb) TF30-9 engine and the totally different 'Mk II' avionics, with mainly solid-state digital circuits. The F-111E (94) had only improved engine inlets, otherwise resembling an A. The final F-111F version (106) has the vastly improved TF30-100 engine, rated at 11385-kg (25100-lb) thrust, and a simpler and cheaper version of the F-111D avionics. In 1967 some $118 million was spent in the development of a multi-sensor reconnaissance pallet which was test-flown in the eleventh F-111A. There remained an intention to rebuild some or all D- models as RF-111Ds.


Since 1976 much further development has been in progress to update this vital and powerful tactical attack force. Grumman has been developing the EF-111A electronic-warfare aircraft by transferring the ALQ-99 tac-jamming system of the EA-6B Prowler to rebuilt F-111A airframes.


In 1965 McNamara, before leaving the Pentagon, announced that 210 strategic bomber versions designated FB-111A would be bought to replace Strategic Air Com-mand's B-58 and older B-52 bombers. Increased costs caused the eventual force to be terminated at only 76, and these equip two small (30-aircraft) wings, styled Bomb Wing (Medium), the 380th at Plattsburgh and 509th at Pease. The FB-111A has a modest engine, the 9230 kg (20350 lb) TF30-7, a so-called 'Mk 2B' avionics system, and the long-span wing and strong landing gear. It can carry a theoretical bombload of 50 free-fall bombs of nominal 340 kg (750 lb), actually weighing a total of 18710 kg (41250 lb). 76 FB-111As were completed in 1971. Using the fuselage and intakes of the F-111E, the FB-111A introduced the larger wings designed by Grumman for the US Navy’s F-111B, plus uprated engines.


The EF-111A was born out of a series of studies undertaken during the late '60s aimed at providing the USAF with a tactical EW system to replace its ageing fleet of EB-66 aircraft. The emergence of ALQ-99E tactical jamming system gave the green light for full scale airframe development and in January 1975, Grumman was awarded a $85.9 million contract for the construction of two prototype EF-111s. These aircraft were in fact preceded by an F-111A fitted with a ventral 'canoe' radome of the type proposed for the production models and which was used to test the aerodynamics of the installation together with five static airframes which were used in a series of electronic tests. The first fully aerodynamically representative prototype (AF serial 66-0049) made its maiden flight on 10th March, 1977 and was followed by a second aircraft (66-0041) which carried a complete electronic suite on 17 May 1977. Both aeroplanes were involved in an 84 flight company test programme and an 86 flight evaluation by the USAF.


Surplus F-111A airframes were chosen for the programme and Grumman was assigned the task of converting the type into a dedicated EW platform.


In November 1979, full scale production of the EF-111A was sanctioned and the two prototypes were re-worked to definitive standard. Aircraft number 049 reappeared on 19th June, 1981 and was initially retained by Grumman for further testing whilst 041 became the first 'production' aircraft to be delivered to the USAF.


Despite outward appearances, the EF-111A is a virtual re-build of the original aircraft. During conversion, Grumman remove the wings and tail surfaces and strip the fuselage back to a basic keel structure. When the re-build is complete, the original components have a fatigue life of approximately 8,000 hrs whilst the new features are rated for 10,000 hrs.


The forward avionics bay remains unchanged and con-tinues to carry the AN/APQ-160 navigation and the AN/APQ-110 terrain following radars which are standard to the F-111A. Aft of the radar boxes, a new oxygen converter has been installed along with a considerable quantity of new electronic equipment, the exact nature of which has not yet been cleared for publication.


The basic geometry of the crew escape capsule is retained but the right-hand side of the cockpit has been completely re-built to house an electronic warfare officer (EWO) and his related controls. The pilot's instrumentation remains essentially similar to that carried by the original aircraft but with some additions and re-arrangement of individual items.


Aft of the cockpit, the weapons bay has been extensively re-worked to house the transmission and other elements of the Al-Q-99. The installation takes the form of a pallet structure hung across the bay with nine transmitters attached to its underside and a range of related electronics above.


Completing the weapons bay modifications is a 4.9m long canoe' radome for the ALQ-99's transmission antenna built into the underside of the bay doors. The elec-tronics pallet is quoted as weighing 1,939kg with the 'canoe' adding a further 210kg, giving a total installation weight of 2,149kg. To provide power for the system, the original 60kVA engine mounted generators have been replaced with units rated at 90kVA. To cope with this increase, a new electrical sub-system has been installed involving extensive re-wiring. To cope with the heat output of the palletised ALQ-99, two new environmental control systems have been installed, namely the air cycling system from the F-111F and a refrigeration system to provide a constant 4.4 degrees C air flow for electronics cooling. The air cycling unit uses a ram air intake below the starboard main engine inlet duct and two exhausts mounted on either side of the rear of the under fuselage. The remaining modification of note concerns the vertical tail surface which has been re-stressed to carry a fin-top fairing and four side blisters designed to house a systems integrated receiver (SIR) group which is used to provide threat data for the various onboard EW systems. The fin-top 'pod' is produced by Canadair and weighs, fully equipped, a respectable 432kg. An integral 'glove' is used to fair the installation into the vertical surface. The standard F-111A vent tank and HF antenna are re-tained within the fin structure.


The EF-111A flew in production form on 28 June 1981. Production Ravens achieved an initial operational capability in November 1983 and entered service with a USAF unit in England in 1984. The 42nd and last was delivered in December 1985.

 

Gallery

 

F-111A
Engines: 2 x Pratt & Whitney TF30-P-3 turbofan 12.500/21,000 lb (5,670/9,525 kg).
Wing span: 63 ft 0 in (19.20 m) fully forward, 31 ft 11.5 in (9.74 m) fully swept.
Length: 73 ft 6 in (22.40 m).
Height: 17 ft 1.5 in (5.22 m).
Gross weight: approx 80,000 lb (36287 kg).
Max speed: 1,650 mph (2,655 km/h) above 36,000 ft (11,000 m).
Max range (internal fuel): 2,750 (4,425 km).
Crew: 2.

EF-111A
Engine: 2 x P&W TF30-P-3 turbofan, 18,500 lb thrust.
Installed thrust: 164.6 kW.
Wing span: 19.2-9.8 m (63-32 ft).
Length: 23.16m.
Height: 6.10m.
Wing area: 48.8 sq.m
Empty wt: 25,070 kg.
MTOW: 40,340 kg.
Max combat speed: 2,216 kph.
Initial ROC: 5690  m / min.
Service ceiling: 13,715 m.
T/O run: 1350 m.
Ldg run: 600 m.
Fuel internal: 19,000 lt.
Ferry range (on internal fuel): 3,706km.
Unrefuelled endurance: 4 hr plus.
Combat radius: 370-1,495km.

F-111B

First fight: 18 May 1965.
Wing span: 70 ft.
Length: 67 ft 6 in

FB-111
Span: 72.5deg 10.34 m (33 ft 11 in); 16deg sweep 21.34 m (70 ft)
Length: (with probe) 23.1 m (75 ft 9.5 in)
Gross weight: (after in-flight refuelling) 55747 kg (122900 lb)
Maximum speed: (Sea level, clean, most versions) 1346 km/h (836 mph, Mach 1.1); (high altitude, clean) 2335 km/h (1450 mph, Mach 2.2)

FB-111A
Engines: 2 x Pratt & Whitney TF30-P-7 turbofan, 20,350 lb thrust.
Armament: six SRAM missiles (or nuclear bombs) or up to 31,500 lb (14,288 kg) of conventional bombs.

F-111C
Engine: Two Pratt and Whitney TF-30 turbofans (9,500 kg thrust each)
21.3m extended, 10.3m swept
Sweep: 72.5-16deg
Length: (with probe) 23.1 m (75 ft 9.5 in)
Height: 5.3m
Basic Weight: 24,000kg
Gross weight: 51846 kg (114300 lb)
Maximum speed: (Sea level, clean, most versions) 1346 km/h (836 mph, Mach 1.1); (high altitude, clean) 2335 km/h (1450 mph, Mach 2.2)
Crew: 2

RF-111C
Wing span: 19.2 m / 9.8 m (63-32 ft).

F-111D
Span: 72.5deg sweep 9.74 m (31 ft 11.5 in); 16deg sweep 19.2 m (63 ft)
Length: (with probe) 23.1 m (75 ft 9.5 in)
Gross weight: 41958 kg (92500 lb)
Maximum speed: (Sea level, clean, most versions) 1346 km/h (836 mph, Mach 1.1); (high altitude, clean) 2335 km/h (1450 mph, Mach 2.2)

F-111E
Span: 72.5deg sweep 9.74 m (31 ft 11.5 in); 16deg sweep 19.2 m (63 ft)
Length: (with probe) 23.1 m (75 ft 9.5 in)
Gross weight: 41958 kg (92500 lb)
Maximum speed: (Sea level, clean, most versions) 1346 km/h (836 mph, Mach 1.1); (high altitude, clean) 2335 km/h (1450 mph, Mach 2.2)

F-111F
Span: 72.5deg sweep 9.74 m (31 ft 11.5 in); 16deg sweep 19.2 m (63 ft)
Length: (with probe) 23.1 m (75 ft 9.5 in)
Gross weight: 45360 kg (100000 lb)
Maximum speed: (Sea level, clean, most versions) 1346 km/h (836 mph, Mach 1.1); (high altitude, clean) about Mach 2.5.

F-111G
Wing span: 19.2 m / 9.8 m (63-32 ft).

 

gd-f111-ld

 

 


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