Northrop YA-9 and little-known design studies for the A-X program from the Southern California aviation industry

Much has been written about the late 1960s-early 1970s A-X program by the US Air Force for a dedicated ground attack aircraft, with emphasis on the two competing aircraft involved in the A-X competition, the Fairchild-Republic A-10 Thunderbolt II and the Northrop YA-9, of which the former was declared the winner of the A-X contest. For the most part, the fly-off between the YA-9 and A-10 as part of the A-X competition was one aspect of the 'fly-before-buy' method concocted by the USAF at times whereby two or more designs for an aircraft competition were selected for prototyping, and the Pentagon could evaluate those designs to decide on which aircraft should be selected for production. During my first visit to the March Field Air Museum in Riverside, California, I got the chance to see the YA-9 for the first time in person back in December 2018, marveling at the placement of the YA-9's engines and the sleek fuselage. Thanks to project documents in the archives of southern California aircraft manufacturers contained in the books American Secret Projects: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974 (Midland Publishing, 2010) and Convair Advanced Designs II: Secret Fighters, Attack Aircraft, and Unique Concepts 1929-1973 (Crecy Publishing, 2013), it is apparent that Northrop wasn't the only aircraft manufacturer in southern California to submit a design bid for the A-X program.

In the first two decades of the Cold War, the US Air Force viewed long-range combat aviation, strategic mobile airlift, and air defense as paramount priorities for US military aviation, putting ground attack aviation on the back burner. However, combat experience the Vietnam War involving the Douglas A-1 Skyraider highlighted pitfalls in the USAF's ground attack capabilities, so beginning in mid-1966, the Air Force launched the A-X program to begin shopping for an aircraft exclusively designed for close air support missions, including taking out Warsaw Pact armored vehicles stationed in Eastern Europe. The initial A-X requirements, which called for long loiter time, extreme survivability, and massive cannon firepower, requested that any design submission rely on use of turboprop engines. However, by May 1969, the Air Force tweaked the A-X design parameters to require that ground attack aircraft design bids be powered by turbofans (Jesse and Engbrecht 1994, p. 58).

                                                           

Unrealized A-X designs by the southern California aerospace industry: Northrop N-308 V-tailed pusher turboprop design study (top); three-view drawing of the General Dynamics (Convair) Model 70 high-wing attack aircraft (bottom left); three-view drawing of the Lockheed CL-1400-1 attack aircraft with underwing nacelles.  

No fewer than half a dozen aircraft companies submitted design bids as part of the A-X competition (see Buttler 2010, pp. 175-181). Of these companies, four of them (Convair-San Diego division of General Dynamics, Lockheed, North American, Northrop) were based on southern California. Northrop's first design studies for the A-X competition, under the N-308 designation, ranged from tractor turboprop attack aircraft designs to a V-tail attack aircraft with a Lycoming T55 turboprop in pusher configuration (Chong 2016, pp. 177-179). The Northrop YA-9 (company designation N-320) has been described extensively by Wagner (2004) and Chong (2016), but it can be readily summarized as a design with Lycoming F102 turbofan engines buried in the wing roots (similar to Russia's Sukhoi Su-25 ground attack aircraft), a single vertical stabilizer, and underwing pylons for anti-tank weapons, and prior to design of the N-320, Northrop proposed two jet-powered A-X designs, one with rear fuselage mounted turbofans and another with F102s buried in the wing roots, the latter closely resembling the YA-9 (Chong 2016, p. 185). Convair's A-X study, the Model 70, was a high-wing design powered by two General Electric TF34 turbofans slung under the wings, and it had six underwing weapons pylons with provisions for carrying bombs under the wings on the fuselage corners (Bradley 2013, pp. 261-266). Lockheed's A-X design study, the CL-1400, was quite similar to Lockheed U-2 spy plane in having engines buried in the wing roots and a pair of wing nacelles, and it had ten underwing pylons for air-to-surface weapons, two situated between the air intakes and wing nacelles, and eight outside the undercarriage (Buttler 2010, p. 180; see drawing on p. 182). Lastly, the North American NA-339 design (for which only an artist's conception exists) was apparently similar to the N-312 in having turbofans on the upper sides of the rear fuselage, and armament comprised a guns under the nose, bombs mounted under the inner wing sections and fuselage, and (unusually) wingtip-mounted rocket pods (Buttler 2010, p. 177).

Selected photos of the Northrop YA-9, losing competitor to the A-10 Thunderbolt II: second YA-9 prototype (serial number 71-1368) at the March Field Air Museum in Riverside, California; first YA-9 prototype (serial number 71-1367) in flight.

By December 18, 1970, the Northrop N-320 and Farchild Republic proposals were selected by the USAF for prototyping and a subsequent fly-off. The Northrop and Fairchild Republic designs were designated A-9 and A-10 respectively, and the first flight of the YA-9 took place on May 30, 1972 with Northrop test pilot Lew Nelson at the controls. From October 10 to December 9, the A-9 and A-10 prototypes entered a fly-off competition, and on January 10, 1973, the A-10 was declared the winner of the A-X competition. The engine arrangement probably played a role in the USAF's decision to chose the Fairchild Republic design over the Northrop design, because the Air Force top brass was concerned about the wing root-mounted engines of the A-9 being vulnerable to anti-aircraft artillery during combat missions, whereas the location of the A-10's TF34 engines on the rear fuselages were very likely to give the A-10 greater survivability in wartime conditions. Also, the F102 powerplant for the A-9 was still in the testing phase, while the TF34 used to power the A-10 had recently passed test runs, being cleared for production (Jesse and Engbrecht, 1994, p. 59).

The story of the Northrop YA-9 can be seen as one of rigorous and painstaking evaluation of various designs for jet-powered attack aircraft from southern California aircraft companies by the USAF, considering the diversity of engine layouts for the different A-X proposals conceiving by Northrop, Lockheed, North American, and General Dynamics. However, the engine layout of the YA-9 ensured that the Pentagon would deny Northrop the chance to build America's first production attack aircraft since World War II.

References:

Bradley, R., 2013. Convair Advanced Designs II: Secret Fighters, Attack Aircraft, and Unique Concepts 1929-1973.. Manchester, UK: Crécy Publishing.

Buttler, T., 2010. American Secret Projects: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974. Hinckley, UK: Midland Publishing.

Chong, T., 2016. Flying Wings & Radical Things: Northrop's Secret Aerospace Projects & Concepts 1939-1994. Forest Lake, MN: Specialty Press.

Jesse, W., and Engbrecht, B., 1994. Not Quite Ten: Northrop's A-9, A-X runner-up. Air Enthusiast

64 (July–August): 57–59.