|Maiden flight||21 December 1964|
|Primary user||United States Navy|
|Developed from||F-111 Aardvark|
The General Dynamics/Grumman F-111B was a American fighter-interceptor aircraft designed in the 1960s.
The F-111 pioneered several technologies for production military aircraft, including variable geometry wings, afterburning turbofan engines, and terrain following radar for low-level, high-speed flight. Its design was highly influential, particularly for Soviet engineers, and some of its advanced features have since become commonplace. In its inception, however, the F-111 suffered a variety of development problems, and several of its intended roles, such as naval interception, failed to achieve production.
Design and development
The beginnings of the F-111 were in the TFX program, an ambitious early 1960s project to combine the U.S. Air Force requirement for a fighter-bomber with the U.S. Navy's need for a long-range carrier defense fighter to replace the F-4 Phantom II and the F-8 Crusader. The fighter design philosophy of the day concentrated on very high speed, raw power, and air-to-air missiles.
Air Force specifications
The USAF's Tactical Air Command (TAC) was largely concerned with the fighter-bomber and deep strike/interdiction roles, which in the early 1960s still focused on the use of nuclear weapons. The aircraft would be a follow-on to the F-105 Thunderchief, which was designed to deliver nuclear weapons low, fast and far. Air combat would be an afterthought until encountering MiGs over Vietnam in the mid 1960s. In June 1960 the USAF issued a specification for a long-range interdiction/strike aircraft able to penetrate Soviet air defenses at very low altitudes and very high speeds to deliver tactical nuclear weapons against crucial Soviet targets like airfields and supply depots. Included in the specification were a low-level speed of Mach 1.2, a high-altitude speed of Mach 2.5, a combat radius of 890 mi (1,430 km), good short-field performance, and a ferry range long enough to reach Europe without refuelling.
Meanwhile the US Navy had, since 1957, been searching for a long-range, high-endurance interceptor to defend its carrier groups against the new generation of Soviet jet bombers, which by then were being armed with huge anti-ship missiles with nuclear warheads. The Navy needed a Fleet Air Defense (FAD) aircraft with better loitering performance and load-carrying ability than the F-4 Phantom II, and one equipped with a powerful radar and a battery of long-range missiles to intercept both bombers and their missiles.
The Navy had studied, but rejected, a slow straight-winged missile carrier, the F6D Missileer. In December 1960 the Navy had been reconsidering variable geometry for the FAD requirement. The trend toward ever bigger, more powerful fighters posed a problem for the Navy: the current generation of naval fighters were already barely capable of landing on an aircraft carrier deck, and a still larger and faster fighter would pose even greater problems. An airframe optimized for high-speed — most obviously with a high-angle swept wing — is inefficient at cruising speeds, which reduces range, payload, and endurance, and leads to very high landing speeds. On the other hand, an airframe with a straight or modestly swept wing, while easier to handle and able to carry heavy loads over longer distances on a minimum of fuel, has lower ultimate performance. Variable geometry, which the Navy had tried and abandoned for the XF10F Jaguar in 1953, offered the possibility of combining both in a single airframe.
The F-111B was to be a fleet-defense fighter for the US Navy, fulfilling a long-standing naval requirement for a fighter capable of carrying heavy, long-range missiles to defend carriers from Soviet anti-ship missiles. The Navy had just cancelled the F6D Missileer, a concept for a slow, straight-winged jet with the advanced Hughes AN/AWG-9 pulse-Doppler radar, which could detect low flying targets among ground clutter, and lift eight new AIM-54 Phoenix long range, air-to-air missiles, which could attack multiple aircraft simultaneously at ranges out to 100 miles. The concept was soon cancelled, but the F-111 offered a platform with the range, payload, and Mach 2 performance of a fighter to intercept targets quickly, but with swing wings and turbofan engines, it could also loiter on station for long periods. The F-111B would carry six Phoenix missiles, but have no gun or other short range armament. General Dynamics, having no experience with carrier-based aviation, partnered with Grumman for this version.
The F-111B was a compromise that attempted to reconcile the Navy's very different needs with an aircraft whose basic configuration was largely set by the USAF need for a supersonic strike aircraft, and those compromises would harm both versions. The side-by-side seating was preferred by the Navy from the Missileer. The B was shorter than the F-111A, to enable it to fit on carrier lifts, but had a longer wingspan (70 ft/21.3 m compared to 63 ft/19.2 m) for increased range and cruising endurance. Although the Navy had wanted a 48-inch (122 cm) radar dish for long range, they were forced to accept a 36-inch (91.4 cm) dish for compatibility. The Navy had requested a maximum takeoff weight of 50,000 lb (22,686 kg), but Secretary of Defense McNamara forced them to compromise at 55,000 lb (24,955 kg). This weight goal proved to be overly optimistic. Excessive weight plagued the B throughout its development. Not only were prototypes far over the 55,000 lb (24,955 kg) limit, efforts to redesign the airframe only made matters worse. The excessive weight made the aircraft seriously underpowered. In landing configuration at carrier weights, the F-111B could not maintain level flight on one engine, which would be a major problem once committed to the approach. Worse, its visibility for carrier approach and landing was abysmal.
Requirements for the F-111B had been formulated before air combat over Vietnam in 1965 showed the Navy still had a need for an aircraft which could engage MiG fighters at close range. The Navy desired a fighter with more performance than the F-4 Phantom II, yet in trials, the maneuverability and performance of the F-111B, especially in the crucial medium-altitude regimen, was decidedly inferior to the Phantom. During the congressional hearings for the aircraft, Vice Admiral Thomas "Tom Cat" Connolly, then CNO (Air), famously responded to a Senator's question as to whether a more powerful engine would cure the aircraft's woes, "There isn't enough power in all Christendom to make that airplane what we want!"
By October 1967, the Navy was finally convinced that the F-111B program was a lost cause and recommended its cancellation, which occurred in 1968 after seven had been delivered, two of which had crashed. The swing-wing configuration, TF-30 engines, Phoenix missiles and radar developed for this aircraft (and the earlier, cancelled F6D Missileer) were used on its replacement, the F-14 Tomcat, also designed by Grumman. The Tomcat would be large enough to carry the AWG-9 and Phoenix weapons system while exceeding the agility of the F-4 Phantom.
Data from Quest for Performance
- Crew: 2 (pilot and weapons system operator)
- Length: 73.5 ft (22.4 m)
- Spread: 63 ft 0 in (19.2 m)
- Swept: 32 ft 0 in (9.75 m)
- Height: 17.13 ft (5.22 m)
- Wing area:
- Spread: 657.4 ft² (61.07 m²)
- Swept: 525 ft² (48.77 m²)
- Airfoil: NACA 64-210.68 root, NACA 64-209.80 tip
- Empty weight: 47,481 lb (21,537 kg)
- Loaded weight: 82,843 lb (37,577 kg)
- Max takeoff weight: 98,979 lb (44,896 kg)
- Powerplant: 2× 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 coefficient: 0.0186
- Drag area: 9.36 ft² (0.87 m²)
- Aspect ratio:
- Spread: 7.56
- Swept: 1.95
- Maximum speed: Mach 2.5 (1,650 mph, 2,655 km/h)
- Combat radius: 1,330 mi (1,160 NM, 2,140 km)
- Ferry range: 3,220 mi (2,800 NM, 5,190 km)
- Service ceiling: 56,650 ft (17,270 m)
- Rate of climb: 25,890 ft/min (131.5 m/s)
- Wing loading:
- Spread: 126.0 lb/ft² (615.2 kg/m²)
- Swept: 158 lb/ft² (771 kg/m²)
- Thrust/weight: 0.61
- Lift-to-drag ratio: 15.8
- Guns: 1× M61 Vulcan 20 mm (0.787 in) gatling cannon (seldom fitted)
- Bombs: 31,500 lb (14,300 kg)
- ↑ Time magazine
- ↑ Loftin, LK, Jr. Quest for performance: The evolution of modern aircraft. NASA SP-468. Retrieved: 22 April 2006.
- Thornborough, Anthony M. F-111 Aardvark. London: Arms and Armour, 1989. ISBN 0-85368-935-0.
- Winchester, Jim, ed. "General Dynamics FB-111A." "Grumman/General Dynamics EF-111A Raven." Military Aircraft of the Cold War (The Aviation Factfile). London: Grange Books plc, 2006. ISBN 1-84013-929-3.
- Royal Australian Air Force F-111 page
- F-111 profile on Aerospaceweb.org
- F-111 on ausairpower.net
- F-111 page on GlobalSecurity.org
- Are the F-111's Really Stuffed? by Don Middleton ADA Defender Summer 2006/07
- Report of the RAAF Evaluation Team for a replacement Strike/Reconnaissance Aircraft for Air Staff Requirement (ASR) 36 from the National Archives of Australia
- F-111 page on USAF National Museum web site
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