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A-X competition
Designed by Northrop in the early-1970s, the YA-9 Ground Attack Aircraft was developed in response to a request by the US Air Force (USAF) for a rugged, close air support aircraft capable of destroying the heaviest Soviet tanks and armored vehicles. Envisioned as a “flying tank” the A-9 was designed with low-level survivability in mind. In fact, the A-9 could withstand multiple direct hits from Soviet 23mm anti-aircraft cannons.
Unfortunately for the A-9, its competitor in the close air support (later to be called Attack-Experimental, A-X) competition was the now legendary Fairchild Republic A-10 Thunderbolt II, possibly the greatest ground attack aircraft ever designed.
Only two YA-9A prototypes were built by Northrop Aviation.
As told by Don Logan in his book Republic’s A-10 Thunderbolt II, A Pictorial History, following rollout of the first YA-9A (serial number 71-1367) at Hawthorne in March, 1972 the prototype No. 1 was prepared for shipment to Edwards Air Force Base for flight test. It first flew on May 30, 1972, piloted by Northrop test pilot Lew Nelson. He described the 58 minute test flight as “routine’ and “as planned.” The second prototype was given the serial number 71-1368.
YA-9 preliminary design
The YA-9 preliminary design was centered on a rugged, twin-engine, single-place aircraft with Short Take Off and Landing (STOL) capabilities and excellent maneuverability. |t carried a varied payload, was capable of long loiter time over the target area, and had high survivability against enemy ground fire.
The YA-9 prototypes’ primary construction was all-metal riveted aluminum alloy, semi-monocoque with stressed skin. Extensive use was made of honeycomb structure and chemically-milled skins. The YA-9 was a high-wing aircraft powered by two AVCO Lycoming YF102-LD-100 turbofan engines, developed under subcontract to Northrop. Each engine developed 7,500 pounds of thrust. The engines were mounted in nacelles on either side of the fuselage just below the wind trailing edge. The pilot sat in a protective “bathtub” of aluminum armor (titanium was the metal planned for the production version). A bubble canopy gave the pilot a 360 degree over-the-nose visibility to reduce chances of a surprise attack and provide optimum target observation.
The YA-9 also featured foam-filled fuel tanks in the wings well away from ignition sources. Redundant flight control systems afforded additional safeguard against battle damage. If one of the primary hydraulic systems became inoperable, the other would continue to function. A third manual backup system added a final measure of safety in the event both hydraulic systems failed.
Maintenance was “designed into” the aircraft. All servicing functions could be performed at ground level. The easily replaced engines were chest-high on either side of the fuselage. Engine removal and installation was timed taking less than 60 minutes.
The 58-foot span wing was equipped with ten hardpoints for external carriage of mixed ordnance. Long Fowler-type flaps extended over half the wing span on both sides of the fuselage.
YA-9 prototypes equipped with a single 20mm gun
Large ailerons on the outboard third of the wing were split into upper and lower sections, serving both as speed brakes and ailerons. This split aileron design feature, pioneered in earlier Northrop designs, was also used on the A-10. Flap-width spoilers on the upper wing trailing edge helped to kill lift in short-field landings. The rudder and vertical stabilizer were large, affording a high degree of directional stability.
Stability was also enhanced by a pitch-and-yaw-axis stability augmenter. In addition, the large, movable rudder surface was an essential element in the Northrop-designed “side force control” system. This system made use of the rudder and asymmetric application of the split-aileron speed brakes to provide sideward forces to the aircraft without need for banking. Yaw control by differential use of split ailerons was later used by Northrop to control yaw in the tail less B-2.
Ability to displace the aircraft sidewards without banking and S-turning eliminated the resultant yawing and pitching reactions that could delay or upset target tracking. Studies showed that in a 45-degree bombing run, the YA-9 could achieve up to twice the tracking accuracy with “side force control” than without it.
The production version of the A-9 was to use the GAU-8 30mm Gatling-type cannon then under development. This cannon was to be mounted in the belly, its barrel extending through a slot in the fuselage beneath the cockpit to a point just ahead of the off-center nose gear. The gun was mounted along the longitudinal centerline of the fuselage to eliminate recoil effects about the yaw axis. As a result of gun location, the nose landing gear was displaced one foot to the left of the centerline. For the flight and evaluation tests, both YA-9 prototypes were equipped with a single 20mm gun.
Fly off against the YA-10
Following development flight tests by the company, both YA-9 prototypes were turned over to the Air Force in the fall of 1972 for flight evaluation.
Air Force testing of the YA-9 and YA-10 began at Edwards AFB in October, 1972. Pilots from Air Force Systems Command and Tactical Air Command flew the YA-9 for 307.6 hours and the YA-10 for 328.1 hours before the evaluations were completed in early December, 1972.
Throughout the fly off, differences between the competitors were identified and explored in a series of difficult flying profiles. On January 18, 1973, the Office of the Secretary of Defense announced the selection of the A-10 design as winner of the A-X competition, and approved full-scale development of the A-10A.
Very little difference in weapons delivery accuracy existed between the two designs, but the A-10 design exhibited superior ground handling qualities and had easier hardpoint access under a wing with more room for ordnance. As a result of Fairchild’s gamble of asking for more money for their initial prototypes, the YA-10 design was closer to production, with a simpler design and requiring less transition difficulty in bringing the aircraft into full production. It appeared likely this would keep the flyaway cost closer to the then estimated $1.4 million per aircraft.
YA-10 wins A-X competition
On the first of March. 1973, Fairchild Industries was awarded a $159,279,888 cost-plus-incentive-fee contract to continue prototype aircraft testing, and to develop and build 10 preproduction aircraft. Concurrently, General Electric was awarded a $27.666,900 firm fixed price incentive contract for development of 32 TF-34 engines to power the A-10. Cost of the A-10 was expected to be $1.5 million per airplane in 1970 dollars, based on a buy of 600 aircraft, to be delivered at the rate of 20 per month, once production got underway. Costs were stated in 1970 dollars.
On June 21, 1973 the Air Force announced the completion of contract negotiations with General Electric for the GAU-8 cannon. They were awarded a $23,754,567 firm fixed price incentive contract for three preproduction models to be used for quality testing and eight preproduction models to be installed in the A-10As.
While the YA-9A was assessed to be an excellent aircraft, it did not win the production contract.
The YA-9A supported Northrop’s belief that a close air support fighter could be built for $1.4 million flyaway price in 1970 dollars. Both YA-9 prototypes were eventually transferred to NASA for its own aerodynamic test programs, and later placed in museums. The first prototype 71-1367 was displayed in Merced, California at the museum adjacent to the now closed Castle AFB. 71-1367 is now at Edwards AFB as part of the AFFTC Museum collection. The second aircraft, 71-1368 is on display at the March AFB, California museum.
Republic’s A-10 Thunderbolt II, A Pictorial History is published by Schiffer Military and is available to order here.
Photo credit: U.S. Air Force
