RogerBW's Blog

North American A-5 Vigilante 07 April 2014

The Vigilante was a carrier-borne supersonic bomber.

Like the B-58 Hustler of a few years earlier, it was designed to fight a nuclear war: to fly high and fast to avoid ground fire and interceptors, and to drop a single large bomb. Intended to replace the subsonic A-3 Skywarrior in US Navy service, it was a descendant of the XF-108 Rapier design (a proposed Mach 3 interceptor counterpart to the Mach 3 XB-70 Valkyrie).

Unlike many high-altitude aircraft, its shape is fairly conventional: a high-mounted swept wing (with some delta-like characteristics), and a large tailplane. However, it was distinctly sophisticated, particularly for its era: to improve low-speed lift it had an early blown-flap boundary layer control system, it used one of the first fly-by-wire control systems, it carried an inertial navigation system, and the cockpit featured an early HUD ("Pilot's Projected Display Indicator").

It ran on a pair of J79s, the same engine used in the B-58, but sensibly kept them close to the centreline to avoid spin problems. In order to be able to drop bombs cleanly at supersonic speeds, its bomb bay was of a unique design: rather than opening downwards, it consisted of a tube running the length of the aircraft between the engines, with an opening between the jet nozzles. It would in theory be loaded with a single Mk 28 in front of two disposable fuel pods which would be emptied on the flight towards the target; to drop the bomb, a small explosive charge would project the whole "stores train" assembly backwards out of the aircraft at about thirty knots relative speed. This part of the aircraft never worked reliably, and live weapons were never actually carried; on three occasions, the stress of a carrier launch knocked the stores train loose from the aircraft, spilling fuel pods across the deck.

Although the high stall speed, and high angle of attack on landing, made it a demanding aircraft to fly, it was popular with pilots; the clean design and good thrust-to-weight ratio made it fast and relatively nimble. (Unlike the Skywarrior, it also had ejection seats.) As one might expect, the large and complex aircraft had a variety of teething problems, particularly with its array of electronic systems. It got a reputation for needing far more maintenance hours than other carrier aircraft, and for in-flight failures.

However, the Vigilante's real problem was that it was came into service in the nuclear strike role around the time that the US Navy was moving its nuclear capability to ballistic-missile submarines. In 1963, two years after its first deployment, the decision was made to convert all aircraft to a reconnaissance configuration.

This involved slightly enlarging the wing, replacing the Mk 28 with a third fuel pod, and adding a ventral fairing for the new equipment (side-looking radar, infra-red scanner, and various cameras). With only a modest increase in thrust and five tons more weight, the plane lost some of its acceleration and climb rate, though it was still fast in level flight. The bombing electronics were retained, and the Vigilante could in theory still carry weapons on its wing pylons, though it never did in service. As a recon aircraft it saw action over Vietnam.

A variant proposed by North American to the USAF, the NR-349 (known in some designs as "Retaliator"), would have used the airframe as the basis for a land-based interceptor, with either a liquid-fuel rocket or a third J79 (presumably mounted in the former bomb bay) to boost performance. This would have carried six AIM-54 Phoenix missiles, presumably to shoot down waves of Soviet bombers. It didn't get very far.

Even by the middle of the 1970s, the Vigilante was still a troublesome and complex aircraft to operate and maintain, and its size consumed precious deck and hangar space. Once the Vietnam War was over, squadrons began to be disbanded, and the last Vigilante flight came in 1979. The reconnaissance role was taken over by fighters, first the F-8 Crusader and RF-4B Phantom and later the F-14 Tomcat.

The A-3 Skywarrior, which the Vigilante was meant to replace, continued in service as a tanker and later an EW platform until 1991.

See also:
Convair B-58 Hustler

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