The Ling-Temco-Vought A-7 Corsair II is a carrier-based subsonic light attack aircraft introduced to replace the United States Navy's A-4 Skyhawk, initially entering service during the Vietnam War. The Corsair was later adopted by the United States Air Force, to include the Air National Guard, to replace the A-1 Skyraider, F-100 Super Sabre and F-105 Thunderchief. The aircraft was also exported to Greece in the 1970s, and Portugal and Thailand in the late 1980s. The A-7 airframe design was based on the successful supersonic F-8 Crusader produced by Chance Vought. It was one of the first combat aircraft to feature a head-up display (HUD), an inertial navigation system (INS), and a turbofan engine.
In 1962, the United States Navy began preliminary work on VAX (Heavier-than-air, Attack, Experimental), a replacement for the A-4 Skyhawk with greater range and payload. A particular emphasis was placed on accurate delivery of weapons to reduce the cost per target. The requirements were finalized in 1963, announcing the VAL (Heavier-than-air, Attack, Light) competition. Contrary to USAF philosophy, which was to employ only supersonic fighter bombers such as the F-105 Thunderchief and F-100 Super Sabre, the Navy felt that a subsonic design could carry the most payload the farthest distance. Theoretically, a "slow fat duck" could fly nearly as fast as a supersonic one, since carrying dozens of iron bombs also restricted its entry speed, but a fast aircraft with small wings and an afterburner would burn more fuel.
To minimize costs, all proposals had to be based on existing designs. Vought, Douglas Aircraft, Grumman and North American Aviation responded. The Vought proposal was based on the successful F-8 Crusader fighter, having a similar configuration, but shorter and more stubby, with a rounded nose. It was selected as the winner on 11 February 1964, and on 19 March the company received a contract for the initial batch of aircraft, designated A-7. In 1965, the aircraft received the popular name Corsair II, after Vought's highly successful F4U Corsair of World War II. (There was also a Vought O2U Corsair biplane scout and observation aircraft in 1920s.)
Compared to the F-8 fighter, the A-7 had a shorter, broader fuselage. The wing had a longer span, and the unique variable incidence wing of the F-8 was omitted. To achieve the required range, the A-7 was powered by a Pratt & Whitney TF30-P-6 turbofan producing 11,345 lbf (50.5 kN) of thrust, the same innovative combat turbofan produced for the F-111 and early F-14 Tomcats, but without the afterburner needed for supersonic speeds. Turbofans achieve greater efficiency by moving a larger mass of air at a lower velocity.
The aircraft was fitted with an AN/APQ-116 radar, later followed by the AN/APQ-126, which was integrated into the ILAAS digital navigation system. The radar also fed a digital weapons computer which made possible accurate delivery of bombs from a greater stand-off distance, greatly improving survivability compared with faster platforms such as the F-4 Phantom II. It was the first U.S. aircraft to have a modern head-up display, (made by Marconi-Elliott), now a standard instrument, which displayed information such as dive angle, airspeed, altitude, drift and aiming reticle. The integrated navigation system allowed for another innovation – the projected map display system (PMDS) which accurately showed aircraft position on two different map scales.
The A-7 had a fast and smooth development. The YA-7A made its first flight on 27 September 1965, and began to enter Navy squadron service late in 1966. The first Navy A-7 squadrons reached operational status on 1 February 1967, and began combat operations over Vietnam in December of that year.
The A-7's integrated weapons computer provided highly accurate bombing with CEP of 60 ft (20 m) regardless of pilot experience. When Vought technical representatives were available to "tweak" the inertial systems, the CEP was often less than five meters for experienced fleet aviators. The inertial navigation system required a mere 2.5 minutes on the ground for partial (coarse) alignment, a big improvement over 13 minutes required in F-4 Phantom II. For newly manufactured E models, the A-7 required only 11.5 man hours of maintenance per mission resulting in quick turnaround and high number of combat-ready aircraft. However, after several years of exposure to the harsh marine conditions aboard aircraft carriers, the maintenance hours per sortie were often twice this amount.
The A-7 offered a plethora of leading-edge avionics compared to contemporary aircraft. This included data link capabilities that, among other features, provided fully "hands-off" carrier landing capability when used in conjunction with its approach power compensator (APC) or auto throttle. Other notable and highly advanced equipment was a projected map display located just below the radar scope. The map display was slaved to the inertial navigation system and provided a high-resolution map image of the aircraft's position superimposed over TPC/JNC charts. Moreover, when slaved to the all-axis auto pilot, the inertial navigation system could fly the aircraft "hands off" to up to nine individual way points. Typical inertial drift was minimal for newly manufactured models and the inertial measurement system accepted fly over, radar, and TACAN updates.
Naval carrier-capable equivalent of the A-7D; AN/APN-185 navigational radar in earlier A-7D is replaced by AN/APN-190 navigational radar, AN/APQ-126 terrain following radar in earlier A-7D is replaced by AN/APQ-128 terrain following radar; 529 built.