The Northrop A-9A was developed in response to a USAF request for a dedicated Close Air Support/ground attack aircraft capable of operating from short unimproved runways, have a long loiter time over the battlefield area and have a relatively high cruise speed to get from the home field to the battle field.
The Air Force issued a request for proposal to 12 aircraft manufacturers. Six companies responded with specific designs and two companies were selected to build prototypes for a fly-off competition. Northrop was one company selected and Fairchild Republic was the other. The Northrop entry was designated A-9 while the Fairchild aircraft was designated A-10.
The A-9A was a high-wing, twin-engine, single-place aircraft. The plane was designed for exceptional maneuverability and had large flight control surfaces. The engines were specifically designed for the project by Lycoming. Each of the YF102-LD-100 turbofans developed 7,500 pounds of thrust at maximum power. Offensive firepower consisted of a 20mm Vulcan cannon and up to 16,000 pounds of ordnance carried on ten external wing stations. The winner of the A-X fly-off would incorporate the 30mm GAU-8 cannon into production aircraft, but the gun was under parallel development during the A-X competition and wasn't ready for flight testing during the fly-off between October and December 1972. The A-9A featured a triple redundant hydraulic system, foam filled self-sealing fuel tanks and armor plating protecting vital systems including a titanium "bathtub" surrounding the cockpit (note: an aluminum "bathtub" was fitted in the prototype).
The first flight of the A-9A was on May 30, 1972, and the fly-off competition ran between Oct. 10 and Dec. 9, 1972. The Air Force selected the A-10 as the winner of the A-X fly-off on Jan. 18, 1973. The two prototype A-9As were transferred to NASA for flight testing before being retired.
AX Fly-off prototype
TECHNICAL NOTES: Armament: One M61A1 20mm cannon and up to 20,000 lbs. of mixed ordnance (bombs, rockets, missiles and dispensers) and/or fuel tanks on 10 external stations Engines: Two Lycoming YF102-LD-100 turbofans of 7,500 lbs. thrust each Maximum speed: 449 mph Cruising speed: 322 mph Range: 3,622 miles Service ceiling: 40,000 ft. Span: 58 ft.
Length: 53 ft. 6 in. Height: 16 ft. 11 in. Weight: 42,000 lbs. maximum takeoff Crew: One Serial numbers: 71-1367 and 71-1368