The A-5 Vigilante

Originally designed as a Mach 2 all-weather bomber capable of delivering nuclear weapons, the A3J (redesignated A-5 in 1962) Vigilante was eventually modified into a high-speed reconnaissance aircraft after the Navy’s strategic bombing mission was assumed by nuclear submarines. The resulting RA-5C Vigilante incorporated sophisticated electronic equipment in its bomb-bay that included side-looking airborne radar and passive electronic countermeasures, along with vertical, oblique and split-image cameras.

Through at least 1959 to 1965, NASA tested several variants of the A3J configuration modified with variable geometry wings. As these are known solely from NASA wind tunnel test reports, details on just what the end goal was is unclear at best. These may have been tests done at the behest of North American, interested in expanding the marketability of the Vigilante; alternatively, these may have been purely theoretical studies, using the existing wind tunnel dataset of the Vigilante configuration as a baseline, In any event, the timing was not entirely accidental.

Variable geometry wings

According to Scott Lowther’s book US Supersonic Bomber Projects, the late 1950s through the 1960s was the heyday of the variable sweep wing; it promised a combination of good low speed takeoff and landing characteristics, good subsonic cruise and loiter performance and low drag at supersonic speed.

A number of aircraft emerged into operational service from this technological fad… the US fielded the F-111, the F-14 and the B-1; the Europeans the Panavia Tornado, the Soviets the MiG- 23 and -27, Su-17, -20 and -22, Su-24, Tu-22M and the Tu-160, most starting life during the 1960s. Since then the excitement of variable geometry wings has faded; the Tu-160 entered service in 1981, the last variable geometry aircraft to do so. And while there have been subsequent proposals for VG aircraft, none have come close to production. The complexity and weight, coupled with advancements in aerodynamics, structures and computerized control systems have made variable geometry far less appealing.

But in its day, variable geometry was all the rage. So, NASA tested a number of A3J-1/A-5 forms using several different sets of variable geometry wings. A very basic system of designations was applied to the various configurations; if there were any other designations, NASA or North American, they are currently lost.

Configuration 1 and Configuration 2

Configuration 1 was wind tunnel tested at up to Mach 1,97, It featured the A3J-1 fuselage and tail mated to variable geometry wings with the pivot points located well outboard of the wing roots. This resulted in large fixed wing ‘gloves’ and smaller movable wing panels. The wings were swept aft to 75°. Canards were used in some tests, both with and without the horizontal tails. The use of canards led to reduced static margin as the wings swept aft. This would have likely required computerized controls; standard practice today, rather more challenging in the early 1960s.

Configuration 2 moved the pivot points inboard within the fuselage. This maximized the size of the wing that could actually sweep back and forth and resulted in a small wing `glove’. This also meant that a large portion of the wings would retract into the interior of the fuselage, requiring a fair amount of space that could not be otherwise used for fuel or engines. It had, however, the advantage of putting the pivot within the thick fuselage, rather than the thin wing glove, meaning the pivot could be stronger to withstand the forces that will be applied to it from many directions.

The A-5 Vigilante variable geometry wings variants that never were (but that paved the way for TFX studies)
A3J configuration modified with variable geometry wings

The main disadvantage was that the aerodynamic centre of the aircraft would shift fore and aft a considerable distance as the wing moved, requiring that the wing either translate fore and aft to compensate (a heavy, complex and space-consuming system) or use large control surface deflections, resulting in considerable drag. The maximum sweep of the wings was 70.5°.

Configuration 3, Configuration III and Configuration IV

Configuration 3 was Configuration 1 modified to allow the wings to sweep even further aft: to 113°. This folded them back onto the fuselage, and resulted in an almost wingless configuration; lift would be generated by the fuselage and the stub wings formed by the wing roots. This configuration was considered most appropriate for a high-speed, low altitude attack aircraft. Clearly no ordnance could be hung under the wings, at least if the plane was going to fully sweep its wings; missile and bombs would have to be carried internally or hung from body-attached pylons.

The design was changed again to produce `Configuration III`, (no explanation was given for the change from Arabic to Roman numerals, nor for the re- use of `Configuration Three`) a double-inboard-pivot configuration. It had a large sweepable wing with an inboard pivot like Configuration 2, but was able to sweep the small wing glove as well.

The advantage of this was that there would be no discontinuities in the wing leading edge as the wing swept fore and aft. This configuration, while more complex than the single pivot designs, demonstrated increased stability. It reduced the unfortunate contribution the glove makes to pitch-up with the wings at full spread. The wing glove retracting into the fuselage as the main wing extended would of course be more complex and require yet more internal volume… but it seemed to negate much of the aerodynamic centre shifting problems of Configuration 2. This design was tested at up to Mach 2.2. Maximum wing sweep was 71.5″.

Configuration IV was much like Configuration III, but with the wing and pivot point translated somewhat further aft.

A-5 Vigilante variable geometry wings configurations useful for the imminent TFX studies

Several years later, another variation was evaluated and reported on. A model with a ‘free floating apex’ was studied in hopes of reducing some of the problems with the double-pivot configuration. Rather than being retracted into the fuselage, the free-floating apex allowed the glove to pitch nose-down like an all- moving horizontal stabilizer. Thus, the lift and drag of the glove could be adjusted for any flight regime; it could be positioned to have a zero angle of attack with respect to the airstream, eliminating lift generation altogether. By being free-floating, the glove would automatically adjust itself to the conditions at hand.

The NASA studies showed definite potential for variable sweep wings, but these were never applied to the actual Vigilante. They would, however, prove useful for the imminent TFX studies.

US Supersonic Bomber Projects is published by Mortons Books and is available to order here.

RA-5C print
This print is available in multiple sizes from – CLICK HERE TO GET YOURS. RA-5C Vigilante RVAH-6 Fleurs, AJ601 / 156620 / 1972

Photo credit: US Navy