Profile -North American A-5 Vigilante

Background

In the 1950s the United States adopted its tripwire policy of massive nuclear retaliation. In this light through to the early 1960s the US Air Force and US Navy battled over which service should be primarily responsible for the delivery of nuclear weapons, a position that was likely to attract substantial funding at the expense of other services and military programmes. For the US Air Force’s Strategic Air Command, this meant procuring vast armadas of long range land based B-36s, B-47s and B-52s, while the US Navy invested in enormously expensive supercarriers from which it could operate squadrons of nuclear armed AJ Savages and A3D Skywarriors.

With new developments in aviation technology running at a frantic pace through the 1950s, the Navy needed a new high performance strategic nuclear bomber to replace its earlier types, with North American Aviation taking up the challenge. North American was brought to great prominence during the war years with its P-51 Mustang, acknowledged as the best US fighter of WW2. This design subsequently being followed up by the FJ Fury and the F-86 Sabre, as well as the Super Sabre, Trojan, Buckeye and their very nature, large area wings are unsuitable to high supersonic speed, particularly at low level. In this regard the resulting compromise was able to achieve a relatively fast Mach 0. 95 at low altitude and Mach 2 at 40,000ft. But maximum weight was also restricted to meet the stringent takeoff requirements, and the wing was 50% greater in area than it would have been for low level speed alone.

Had North American been able to take advantage of variable geometry, or swing wings, the aircraft would have been able to more easily meet the two conflicting requirements. However given the Navy’s unpleasant recent experience with the Grumman XF10F Jaguar (major problems includ- ing weight and complexity) it was unprepared to embrace this radical concept just yet.

Despite the slower than required low level speed the Navy accepted NAGPAW, placing an $US86m contract with North American for two YA3J-1 prototypes, plus two static test articles in September 1956. Just 18 months later in May 1958 the first A3J prototype was rolled out, and the name Vigilante was officially adopted. Following ground testing the Vigilante made its uneventful first flight on August 31 of that year, piloted by NAA’s chief test pilot Dick Wenzel.

Advanced design

Renowned for its large number of new and untested technologies, at the time of its first flight the Vigilante was arguably the most advanced aircraft in the world. The distinctive, elegant and rakish lines of the Vigilante served as a good indication of the innovative and bold design ap- proach taken by the Columbus team, in spite of their little experience in design prior to this programme.

As accepted by the US Navy, the A3J was a very large aircraft (its design empty weight was over 20 tonnes), featuring a large area shoulder mounted swept wing with a low 3. 5% thickness-chord ratio. The two aircrew sat in tandem separate cockpits in the forward fuselage, while the main body of the airframe from the intakes rearwards was considerably larger, and housed two buried General Electric J79 turbojets and an internal weapons bay. Other notable features included the variable geometry air intakes and all moving horizontal tailplanes and vertical fin (in place of a conventional tail and rudder).

Of the several innovations, the variable geometry inlets have been one of the more prominent aspects of the Vigilante to be incorporated into later combat aircraft such as the MiG-25, Su-27 and F-14. The intakes on the Vigilante are angled sharply back from top to bottom, with the variable geometry ramps housed in the roof of the inlets. Actuated simultaneously, the intakes were adjusted by a built-in sensing system that detected the build up of shock waves inside the intakes. The ramps could be adjusted with a maximum angle of up to 23 degrees from horizontal.

One of the most imaginative and unusual design features was the linear bomb bay. Housed in the centre of the fuselage sandwiched between the two J79 turbojets, the ‘special’ or nuclear weapon was ejected rearwards, exiting the aircraft through an opening between the two exhaust nozzles. Running almost half the length of the fuselage, the weapons bay was considerable longer than the bomb it was designed to carry and so either side of the weapon was to be linked to a disposable fuel tank. These tanks were designed to be emptied first and would be jettisoned with the bomb, acting as stabilisers during the fall. A non structural access door in the fuselage underside allowed maintenance, connection and arming of the weapon.

The linear bomb bay and special weapon combination was never employed operationally. Not surprisingly, significant problems were encountered with the system, with the result that weapon separation from the bomb bay was never fully perfected. In service the bomb bay was mostly used to house three additional fuel tanks with a combined capacity of 3350 litres. With the bomb bay used for fuel, weapons carriage on the initial A3J-1 was confined to two underwing stores stations, capable of carrying a variety of ordinance ranging from tactical nuclear bombs through to Bullpup ASMs and conventional iron bombs.

The large wing was also unusual for the period when maximum speed was the general overriding design consideration for many bombers and fighters. In addition to using wing area to generate sufficient lift to takeoff in nil wind conditions, the Vigilante used a sophisticated high lift system. On the A3J-1 this involved a drooping leading edge with a maximum droop angle of 30 degrees on the outboard section while the trailing edge flaps were blown from compressed air bled from the engines. Coming into operation automatically after seven degrees of flap was deployed, air was blown through slots just above the leading edge of the flap to delay the break up of the boundary layer over the flap surface.

Unusually, the wings had no ailerons. Instead, roll control was provided by a system of spoilers and deflectors. A pair of spoilers, hinged at their leading edge, on the wing upper surface, and corresponding deflectors, hinged at their trailing edge, on the lower surface of each wing, would open up so that air would actually flow through the wing. A third set of spoilers and deflectors, outboard from the first pair, re- versed this arrangement, this spoiler also providing yaw compensation.

The all moving tailplanes provided pitch control when used in unison, while in restricted opposition they provided roll trimming. The unique all moving vertical tail meanwhile was in place of a conventional rudder, providing directional control and trim. Initially North American had designed the Vigilante to feature twin vertical tails similar in configuration to that later featured on the F-14, F-15 and MiG-25, among others, but this featured was dropped.

Pioneering the use of fly-by-wire, electrical signals relayed longitudinal and lateral command inputs from the pilot to the respective moving surfaces. For these systems a mechanical backup was available in the event of an electrical failure. Directional inputs however relied on a conventional mechanical system. All moving surfaces were irreversible and hydraulically powered.

North American had considered using compressed nitrogen in place of hydraulic fluid for the main power system, although this idea was dropped in favour of conventional dual hydraulic systems.

In a number of other areas though, the Vigilante did make extensive use of a number of unconventional and exotic materials just becoming available at the time.

Not shy of breaking new ground, the Vigilante will be long remembered for its relatively large scale use of titanium in and around the engine bays. No doubt the use of 1090kg of titanium plus heat reflective gold film in the engine bays contributed greatly to the aircraft’s high cost. The skin also took advantage of modern materials, with large scale use of integrally machined Aluminium Lithium alloy used on the wing and tailplane. Aluminium honeycomb was used for many secondary structures, while chemical and machine milling techniques were used throughout for airframe construction. Steel alloys were used for the undercarriage legs and other load bearing fuselage frames.

The windscreen is also notable, its makers claimed it to be the largest curved one piece laminated aircraft glass made at that time, before stretched acrylic technology was used for aircraft glass.

The rear cockpit in particular drew a great amount of criticism due to the very small windows which greatly limited the navigators vision. A solid canopy with no glass at all was considered at one time, providing a darkened environment for optimum radar viewing, while also protecting the occupant from nuclear blast effects. Primary objections to this arrangement were based around the claustrophobic effects of sitting in such a confined and dark space for long lengths of time. In the end a compromise was reached which provided the two still very small side windows fitted with shutters. Even this arrangement was not the best for the poor navigator who had no forward vision, and when landing had no way of knowing if the pilot was flying a good approach or not, reportedly causing higher than usual levels of apprehension.

Inside the cockpits the aircrew sat on North American HS-1 ejection seats, which initially were effective above 90kt (168kmh) and at all altitudes, but were later modified to have a true zero-zero capability.

The Vigilante was also able to take advantage of the great advances in electronic systems technology occurring dur ing the 1960s. The complex AN/ASB-12 bombing system formed the heart of the Vigilante’s attack avionics, and incorporated work already done by North American for its revolutionary B-64 Navajo strategic missile. It gave the aircraft perhaps the most advanced Automatic Flight Control System (ACFS) yet incorporated into an aircraft design and permitted precise all weather operations.

Key components of the AN/ASB-12 system included a General Dynamics multimode radar housed in the aircraft’s nose, North American’s NASARR radar computer which provided terrain avoidance and weapons delivery data, a Radar Equipped Inertial Navigation System (REINS), a closed circuit television system, an advanced autopilot and a Versatile Digital Analyser.

Most data from the AN/ASB-12 system was displayed to the aircrew via radar display screens, while the NASARR radar computer presented information on a Pilot’s Projected Display Indicator (PPDI), a head up display which provided the pilot with terrain avoidance, altitude, steering and weapon delivery command information.

The high level of complexity of these systems understandably resulted in very low initial mean time between failures (MTBF), in some cases initially as low as a few minutes.

Completing the advanced Vigilante package were two General Electric J79 turbojets. The J79-GE-2 variants fitted to development Vigilantes were rated at 10,350lb (46kN) dry thrust and up to 16,150lb (71. 8kN) thrust with afterburning. Early production A3J-1s were fitted with J79-GE-4s which had the same thrust rating but with steel stator cases and front frames substituted for magnesium alloy. Subsequent production A3J-1s were powered by J79- GE-8s producing 10,900lb (48. 5kN) and 17,000lb (75. 6kN) thrust, while later versions had even more powerful ratings. First flight tested in 1955, by the time the J79 appeared on the Vigilante it was a relatively tried powerplant, having first appeared on the F-104 Starfighter. (In addition the J79 also powered the B-58 Hustler and the F4H Phantom II, both of which were undergoing development at that time. ) When the J79 first appeared it did represent a substantial advance in engine technology, with a far higher thrust to weight ratio than contemporary powerplants, due to the fact that it was America’s first high compression, variable stator turbojet.

Other notable features included an in-flight refuelling probe located on the left hand side of the nose, while to meet the usual aircraft carrier stowage requirements, the Vigilante’s nose and wing tips folded up, while the top half of the vertical tail folded down.

Into service

The Vigilante’s first flight marked the beginning of a very short flying career as a dedicated bomber aircraft. Curiously, despite the US Navy forgoing the strategic nuclear bomber role to the USAF by the early 1960s, the Vigilante escaped cancellation. Instead the US Navy switched the A3J’s role to low level tactical attack, despite the Vigilante being less than ideally suited to this mission: its performance at low level being significantly compromised by the requirement for high altitude supersonic performance.

The Vigilante also attracted a great deal of criticism be- cause of its high costs (due largely to the high R&D costs associated with its advanced systems and the exotic materials used in its construction). The first batch of production aircraft (just nine units) cost $US9m each in 1961, a high price indeed to pay for an aircraft not ideally suited to its given role. Regardless, the Navy pushed on with the attack Vigilante with small numbers ordered throughout the early 1960s (14 in FY 1961; 10 in FY1962 and 24 in FY1963).

Following first flight, the Vigilante underwent the usual gamut of test flying and development work at the Naval Air Test Centre at Patuxent River, Maryland, alongside famous types such as the Phantom and Skyhawk. Generally, testing of the Vigilante proved satisfactory although the programme experienced persistent problems with the linear bomb ejection method. Eventually the use of the bay was abandoned, the space being given over to fuel tanks.

Sea trials from USS Saratoga began in July 1960 when the aircraft proved its ability to successfully operate from a carrier. (The Vigilante was restricted to operating from the very largest of aircraft carriers, its large size making it unsuitable for operations from smaller ships. ) Demonstrating that it truly was a hot ship, a Vigilante also established a new world altitude record for an aircraft car- rying a 1000kg payload on December 13 1960. Flying from Palmdale in California, Cdr Leroy Heath and Lt Larry Moore zoom climbed in an early production A3J-1 to an altitude of 91,451ft (27,893m).

Even as a low level bomber the Vigilante’s time was limited. A small number of operational cruises were made with the A3J-1, the most notable being the first, aboard USS Enterprise in August 1962. This short two month cruise also marked the first operational deployment of the carrier itself, plus the McDonnell F4H-1 Phantom.

The Vigilante’s bomber career was short lived. A number of factors acted against it: troubles with the A3J’s bombing system, the coming availability of the A6F Intruder (inci- dentally the A6F was designed to a very similar specifica- tion to NAGPAW, except without the need for supersonic speed), gust problems at low altitude due to its large wing, the sheer amount of carrier deck and hangar space it took up, the enormous cost of equipping all carrier wings with it, and its overall complexity, contributing to a April 1962 deci- sion to convert the Vigilante fleet to the reconnaissance role. This decision was announced by the then Secretary of Defense Robert McNamara, who noted that the Vigilante’s intelligence gathering capabilities were unmatched by any other aircraft in the fleet.

The A3J-2

At the time this decision was made an enhanced attack version was already flying, even though the A3J-1 was just being introduced to service. The development of this second version (which would form the basis of the reconnaissance Vigilante) begun following the relaxation of the restrictive nil wind takeoff requirement. In permitting a greater maximum takeoff weight, this allowed North American to take advantage of the big wing’s load carrying abilities, and to increase significantly the Vigilante’s fuel tankage, further extending its range. A new fuel tank was fitted over the wing centre section, while two existing tanks were extended, these modifications giving the Vigilante its 610 distinctive hump back look. Other changes included two more underwing pylons, taking the total to four, the more powerful J79-GE-8 engines and increased inlet capture area, plus blowing of the leading, rather than trailing, edges. The other notable external change was the increased span and chord of the trailing edge flaps.

The prototype A3J-2 made its first flight on April 19 1962, with the final 18 A3J-1s on order to be built to the new standard. Only six Vigilantes were completed as A3J-2s before the decision to switch the aircraft’s role to recce, the remainder in this batch being converted to the new reconnaissance A3J-3 configuration.

Recce Birds

A reconnaissance version of the Vigilante was first proposed as a parallel development of the A3J-2. Indeed, the resulting recce A3J-3 was identical to the earlier A3J-2 except for the under fuselage fairing containing a range of cameras, sensors and ECM and a so equipped A31-3 first flew as early as June 30 1962. (Not long after this first flight the US Dept of Defense introduced its new rationalised designation system, with the Vigilante being renumbered the A-5. The A3J-1 became the A-5A; the A3J-2 became the A-5B; while the A3J-3 was redesignated as the RA-5C. ) The RA-5C’s comprehensive suite of sensors and systems were amongst the most capable flying at that time. Comprised of ten bays, the ventral fairing, or canoe as it was more commonly referred to, contained a range of systems permitting all weather day and night operations against a variety of different targets. Each station of the canoe was modular and allowed a range of mission specific equipment to be interchanged, while the whole unit was detachable, with the RA-5C retaining the ability to perform strike missions. In practice the canoe did not degrade aircraft performance to any great degree and was generally left on the aircraft.

The forward most station in the fairing housed either a forward oblique KA-51A or KA-51B serial frame camera for daylight use. Behind this, the second station was home to a vertical serial frame camera for use by day or night, depending on the exact sensor fitted, while station 3 contained passive electronic countermeasures (PECM) in the form of an AN/ALQ-61.

In the centre of the canoe, station four could hold a number of camera modules, the one fitted depending on the mission to be flown. These modules were either oblique left and right facing cameras for daylight use; two panoramic cameras; or two cameras for day and night operations or two split-vertical configured cameras. Directly above the fourth station in the bomb bay was station five, home to a camera control unit, a data converter, a recorder amplifier and some receivers. PECM equipment canisters comprised station 6, which was located behind station five inside the fuselage. Towards the rear of the canoe, station 7 contained an AN/AAS-21 infrared mapping radar, while station 8 housed an AN/APD-7 side looking radar (SLAR). Out on the wings, the two inboard pylons were wired for flasher pods used in night photography, and these were collectively referred to as station nine.

low altitude supersonic pass over the target was the respon- Dissemination of the data accumulated by one high or sibility of the Integrated Operational Intelligence Centre (IOIC) or later the Carrier Intelligence Centre (CVIC). A single pass would yield a range of IR, SLR, PECM and photographic data which through cross referencing (using a special matrix block recorded on each of the stations’ media) and correlation with earlier and later passes allowed intelligence specialists to build a comprehensive and accurate picture of the target area.

The first RA-5Cs were actually originally intended to be A-5Bs, and were from the batch of 18 A-5Bs ordered. An additional 43 RA-5Cs were ordered from FY63, while once production of these were completed, North American began the conversion of 43 of the original 59 A-5As to RA-5C standard. First deliveries of RA-5Cs were to VAH-3 from June 1963, which was soon after renamed RVAH-3 (reconnaissance heavy attack squadron 3) marking its change of role. The RA-5C’s first operational cruise was from USS Ranger with RVAH-5. What was expected to be a routine peacetime cruise changed suddenly after the Gulf of Tonkin incident, when Ranger was diverted to the western Pacific. It was during this cruise that Vigilantes performed the type’s first combat missions over South Vietnam.

In all ten RA-5C squadrons were formed through till 1968, between them making 31 deployments to the Vietnam stead during the war, and while 18 aircraft were lost tre. The Vigilante’s high speed and good range held it in very due to enemy action, the type found its forte in bringing home the pictures.

The best acknowledgement of the Vigilante’s capabilities and suitability as a reconnaissance aircraft though was a 1968 reorder for 36 RA-5Cs to bolster numbers due to the Vietnam war. No other US combat aircraft of the era was ordered back into production because of war losses, most other types were simply replaced by more Phantoms. In- deed the Phantom would have been a logical replacement for the Vigilante as the reconnaissance RF-4B was in service with the USMC, but the RA-5C’s performance and intelligence gathering capabilities were clearly unmatched.

This final batch of Vigilantes incorporated a number of minor enhancements over earlier aircraft. Foremost of these was the more powerful J79-GE-10 engines with 17,5891b (78. 2kN) thrust in afterburner (11,8701b/52. 8kN thrust dry), slightly enlarged intakes and small wing root fillets. These leading edge extensions from the engine in-takes to the outboard edge of the wing’s leading edge improved longitudinal control.

The last of these RA-5Cs were delivered to the US Navy in 1970, by which time a merger with Rockwell in 1967 resulted in North American Rockwell. The name was changed again to Rockwell International in 1973.

By 1974 however Vigilante numbers were down markedly due to the retirement of early build airframes and combat losses. Throughout the remainder of the decade the Vigilante was gradually phased out of service. No doubt expedited by its maintenance intensiveness and unique status in the fleet, the last operational Vigilante squadron, RVAH-7, was disbanded on September 28 1979.

Air Force Vigilantes

A number of projected Vigilante variants were offered to the United States Air Force to meet Air Defense Command’s (ADC) requirements for a high performance interceptor.

As early as mid 1959 the Columbus Division proposed a version of the Vigilante for ADC equipped with a North American Rocketdyne XLR46-NA-2 liquid fuel rocket to boost performance at altitude. Dubbed Retaliator, a number of proposals were considered, but despite the keen interest shown by ADC, nothing came of the concept.

More than a decade later though the interceptor Vigilante reappeared during the early 1970s, this time featuring a third J79 turbojet for a similar USAF requirement for an air defence interceptor. The third engine was to be mounted in the space occupied by the linear bomb bay, while air for the engine would be supplied by bifurcated dorsal intakes. An armament of six semi recessed missiles was proposed. No new interceptor resulted from the requirement though, and ADC soldiered on with its F-1068 and F-101 Bs till the 1980s.

Australian Vigilantes

It is little known that Australia came very close to ordering the Vigilante as a Canberra replacement in 1963. Following a search for a replacement for the RAAF’s Canberra bomber force in the early 1960s, the RAAF’s then Chief of Air Staff, Air Marshall Sir Valston Hancock, recommended that the RAAF purchase 36 Vigilantes after a fact finding mission to the USA and Europe.

Against the background of the ‘Confrontation’ with Indonesia, the Canberra replacement requirement was for a deterrent aircraft able to strike cities and bases in Indonesia,

including Jakarta. Specific requirements included a 1100nm (2038km) attack radius, Mach 2. 0 maximum speed, the ability to fly at low altitude at high subsonic speed and be able to carry two ASMs, six 1000lb bombs and ‘special stores’. The announcement of an intention to order the Vigilante (confirmed by Air Minister Fairbairn in August ’63) was largely due to its immediate availability over the preferred choice at the time, the General Dynamics TFX (later F-111) (other possibilities included the Mirage IV, F-4C Phantom and the BAC TSR-2). The Prime Minister Sir Robert Menzies however later announced an order for 24 F-111s in October 1963 which were due to be delivered in 1967. Ordering the F-111s off the drawing board allowed Menzies not only to be seen to be countering the Red threat, but also delay slightly payment for the high tech, high expense bombers.

To Pasture

lucky enough to join museum collections or become gate Following the Vigilante’s retirement a few aircraft were guardians. Over 30 aircraft were put to pasture at the Davis Monthan storage facility in Arizona, and a few were transferred to the Naval Weapons Centre at China Lake for use in weapons practice, while the balance were scrapped.

The low key retirement of the Vigilante from US Navy service marked the final chapter of this truly remarkable combat aircraft. This costly, massive and complex aircraft embodied a range of ambitious advanced features that guarantees it a place in history not so much for its distinguished service career, but for its ground breaking advances.