The Northrop A-9A was a large ground-attack aircraft which was designed in competition with the A-10 in the early 1970's for the A-X requirement. The Air Force requirement for a dedicated Close Air Support (CAS) / ground attack aircraft included the ability to operate 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 battlefield.
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 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 was a high wing, twin engine, single place aircraft. Designed to provide extremely stable platform for bombing accuracy and for exceptional maneuverability, the plane 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 lbs. of thrust at maximum power. It was also designed to be extremely durable and rugged since most of its flight time was to be spent close to the ground, in range of enemy guns.
Like the A-10, it carried many "hard points" for weaponry beneath its wings. Offensive firepower consisted of a 20mm "Vulcan" cannon and up to 16,000 lbs. of ordnance carried on 10-12 external wing stations. The underwing pylons could carry almost all arms in Air Force inventory. All flight control systems were backed up by identical systems and all vital areas were protected with aluminum alloy armor of 1.25 to 2.5 inches. 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 (an aluminum "bathtub" was fitted in the prototype).
The first flight of the A-9A was on 30 May 1972 and the fly-off competition ran between 10 October and 9 December 1972. Models underwent basic aerodynamic testing and evaluation in Arnold Engineering Development Center's 16-foot transonic propulsion wind tunnel in 1971.
The Air Force evaluation considered tne soundness and adequacy of the competitorsí proposals for development of the A-X aircraft including logistic support considerations, aerospace ground equipment p production planning, maintenance and flight manuals, system test and evaluation, and program control management. This evaluation also included flignt test demonstrations to provide assurance that program objectives can be met in reasonable time and for the estimated cost.
Although the Air Force felt that both proposals were sound and adequate, in the opinion of the Air Force the Fairchild proposal provided a greater amount of development test and operational evaluation prior to the production decision date. Also, as a result of the firmness of the A-10 design, Fairchildís proposal was more definitive and required less clarification to ensure its adequacy and soundness than Northropís.
The Air Force selected the A-10 as the winner of the A-X fly-off on 18 January 1973. Although it was not chosen for production, the A-9A was a formidable aircraft in its own right. The two prototype A-9A's were transferred to NASA for flight testing before being retired. One A-9A is currently in the March Field Museum at March Air Force Base. The other is on display at the Castle Air Museum in California.
The first Soviet reference to US fixed-wing CAS aircraft was after the early rounds of the 1972 A-9/A-10 fly-off competition. Yu. Orobev in a 1972 issue of Aviatsiya i kosmonavtika was particularly impressed with the A-9's maneuverability, which he attributed to the aircraft's Side Force Control system. V. Deryabin in a 1973 PVO Herald article also stressed the good maneuverability, as well as good vision and superior armor-plating of the A-9.37 In general, both articles evinced a partiality towards the A-9, and it is thus interesting to compare the official American positions for choosing the A-10 over the A-9 with the published Soviet assessments.
In contrast then, while Soviet analysts appeared to concentrate on the survivability and superior avionics as their criteria for preferring the A-9, US planners saw versatility and economic factors as the attributes most desired in a ground-attack aircraft. The final twist to this episode is that when the first Soviet aircraft specially designed for CAS operations was introduced, the SU-25, it bore a striking resemblance not to the A-10, but the A-9.
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