North American A-5 Vigilante

Design and Development

In 1953 North American Aviation began a private study for a carrier-based, long-range, all-weather strike bomber, capable of delivering nuclear weapons at supersonic speeds. This proposal, the NAGPAW (North American General Purpose Attack Weapon) concept, was accepted by the US Navy, with some revisions, in 1955. A contract was awarded on 29 August 1956. Its first flight occurred two years later on 31 August 1958 in Columbus, Ohio.

At the time of its introduction, the Vigilante was one of the largest and by far the most complex aircraft to operate from a US Navy aircraft carrier. It had a high-mounted swept wing with a boundary-layer control system (blown flaps) to improve low-speed lift, aluminum-lithium alloy for wing skins and titanium for critical structures. It had two widely-spaced General Electric J79 turbojet engines (the same as used on the F-4 Phantom II fighter), and a single large vertical tailfin. The wings, the tail, and the nose radome folded for carrier stowage. The Vigilante had a crew of two seated in tandem, a pilot and a bombardier-navigator (BN)—reconnaissance/attack navigator (RAN) on later recon versions in individual ejection seats.

It was surprisingly agile for such a big and heavy aircraft. Without the drag of bombs or missiles, even escorting fighters found that the clean airframe and powerful engines made the Vigilante very fast at high altitudes. Its high landing speed made returning to the carrier a challenge for inexperienced or unwary pilots.

The Vigilante had extremely advanced and complex electronics. It had one of the first fly-by-wire systems of an operational aircraft (with mechanical/hydraulic backup) and a computerized AN/ASB-12 nav/attack system incorporating a head-up display (Pilot's Projected Display Indicator (PPDI), one of the first), multi-mode radar, Radar-Equipped Inertial Navigation System (REINS, based on technologies developed for the Navaho missile), closed-circuit television camera under the nose, and an early digital computer known as VERDAN (Versatile Digital Analyzer) to run it all. Although this system was highly sophisticated, the technology was in its infancy, and its reliability was poor. In early squadron service the system's MTBF (Mean Time Between Failures) was only 15 minutes.[citation needed] Although some bugs were worked out, the aircraft remained a maintenance nightmare throughout its career.

Its main armament was carried in a novel linear bomb bay between the engines in the rear fuselage which was intended to make bomb delivery safer and more accurate. When conventional bombers "drop" a bomb, the bomb falls downward, but continues forward at the same speed as the aircraft. This requires pilot skill and complicated equipment to place a bomb on its intended target. The linear bomb bay would eject the payload rearward at approximately the same speed as the forward velocity of the aircraft, causing the bomb to "stand still" and drop straight down. No calculation is needed - the bomb falls at the point at which it was dropped. As an added benefit, the aircraft is rapidly moving away from the dropped bomb, enabling lower drop altitudes or safer drops from higher altitudes.

The single nuclear weapon, commonly the Mk 28 bomb, was attached to two disposable fuel tanks in the cylindrical bay in an assembly known as the "stores train." The idea was for the fuel tanks to be emptied during flight to the target and then jettisoned as part of the bomb by an explosive drogue gun. In practice the system was never reliable and often dangerous. The stores train sometimes dropped out during catapult launches, leaving the fuel cells and weapon on the flight deck. It was also prone to "trailing" behind th aircraft in flight. Even later in the Vigilante's career, when the bay was used solely for fuel, the arrangement often proved troublesome.

The Vigilante originally had two wing pylons, intended primarily for drop tanks.

The second Vigilante mark, the A3J-2 (A-5B), incorporated internal tanks for an additional 460 gallons of fuel (which added a pronounced dorsal "hump") along with two additional wing hardpoints, for a total of four. In practice the hardpoints were rarely used. Other improvements included blown flaps on the leading edge of the wing and sturdier landing gear.

The reconnaissance version of the Vigilante, the RA-5C, had slightly greater wing area and added a long canoe-shaped fairing under the fuselage for a multi-sensor reconnaissance pack. This added an APD-7 side-looking airborne radar (SLAR), AAS-21 infrared linescanner, and camera packs, as well as improved ECM. An AN/ALQ-61 electronic intelligence system could also be carried. The RA-5C retained the AN/ASB-12 bombing system, and could, in theory, carry weapons, although it never did in service. Later-build RA-5Cs had more powerful -10 engines with afterburning thrust of 17,900 lbf (80 kN). The reconnaissance Vigilante weighed almost five tons more than the strike version with almost the same thrust and an only modestly enlarged wing. These changes cost it acceleration and climb rate, though it remained fast in level flight.

Wikipedia: A-5 Vigilante