For the A-10A, this large and distinctively quiet turbofan plane was first brought to life by the Close Air Support subcommittee of the Senate Armed Services committee (1967), which recognized and documented that high-speed aircraft (primarily jet aircraft such as the F-4 Phantom II, F-105 Thunderchief, A-7 Corsair II and A-4 Skyhawk) could not be fully effective in the close-air support role of ground forces. With piston-driven A-1 Spads currently fulfilling much of that role in 1967, it was also recognized that having operational airframes 15-20 years old such as these would not long remain servicable. The key for completing any successful CAS mission lay in the visual recognition of friendly and enemy forces—a fundamental requirement that precluded much of then current US inventory: Mach2 Phantom II pilots often were unable to fly slowly with any effectiveness at such low altitudes, and were poorly armored against intense light AAA fire from the ground; sturdier and heavier attack planes such as the Corsair II even had such high attack speeds that after a single target pass, would often find that the enemy had dispersed in the time it took for them to return.
Politically, a dedicated CAS aircraft was vital for the USAF, in order to prevent the Army and the Marine Corps from developing CAS aircraft and (gasp!) flying them independently of the USAF. Such opposition to other branches—particularly the Army—having operational flight squadrons were based on perceptions from the early inception and birth of the Air Corps and then the Air Force itself... suffice it to say that the modern Air Force struggled very hard to be born, and they weren’t going to stand for any Army nonsense, even though the Air Force may have felt distinct pressure to develop just such an aircraft. The shotgun wedding of CAS support to the Air Force has not been necessarily a happy one, despite its recognition of the need for CAS aircraft. In fact, A-10s prior to Desert Storm were scheduled for decommission, retaining only a few for the Forward Air Controller role.
On March 6, 1967, a proposal was made available to 21 companies for design studies of a low-cost attack aircraft, the A-X (Attack-Experimental). The Air Force developed the original specifications for this aircraft, and based on initial reponses, awarded preliminary design contracts to Grumman, Northrop, McDonnell Douglas, and the General Dynamics (Convair division) one month later. The original USAF proposal was revised to include the following: turboprop engines; reductions in overall airframe size, weight and importantly, cost.
The USAF then sent Request for Proposals to 12 of the original 21 companies on May 7, 1970. By August 1970, McDonnell Douglas, North American Rockwell, Beech, Bell Aerospace, Grumman, and LTV declined to bid on the A-X because of the very low cost requirement (and profit margin) projected for the contract. A total of 600 A-X aircraft at a unit price of $1.4 million (1970) dollars each with a contigency inflation allowance of 15% were envisioned in the A-X proposal.
The revised A-X Proposal Requirements were as follows:
1. Ability to deliver highly acccurate weapons against targets with a prime objective to kill tanks.
2. Ability to carry large ordnance payloads and electronic and infrared countermeasures simultaneously.
3. It must have excellent range and loiter capabilities near the battle area.
4. It must be able to maneuver at low altitudes and low to moderate speeds.
5. STOL (short takeoff and landing) capability.
6. Maintain high sortie rates permitting rapid servicing and ease of repair of battle damage.
7. It must be able to survive intense anti-aircraft fire, surface-to-air missiles and attacks by other aircraft.
8. Ease of maintenance.
9. It must be affordable.
Mission criteria included:
1. Recommended use of turbofan engines of between 7,000 and 10,000 lbs of thrust for fuel economy and reduction of IR (heat) signatures.
2. Mission radius - 250 miles
3. Ordnance payload - 9,500 lbs
4. Take-off distance - 4,000 ft
5. Manueverability below a 1,000 ft cloud base.
Interestingly, although the proposal was made at the height of the Vietnam conflict, the proposal was focused on support for a European theater of operations against a (presumably) Soviet advance into NATO-aligned countries.
The remaining six companies returned design proposals: Boeing-Vertol, Fairchild Hiller (Republic division), Cessna, General Dynamics, Lockheed, and Northrop. Then Secretary of the Air Force, Melvin Laird, announced on December 18, 1970 that Fairchild Hiller (Republic division) and Northrop Corporation were the finalists in the A-X project, and invited them to participate in a fly-off. The use of competing prototypes had been uncommon previously, but the requirement for low cost and increasing Congressional disapproval of single source selections put Northrop and Fairchild in a head-to-head competition.
The Competitors: Eyeball to Eyeball
By March 1971, prototype designations were assigned: Northrop A-9, and Fairchild A-10, and two prototypes each were constructed: Northrop YA-9s 71-1367 & 71-1368, and Fairchild YA-10s 11369 & 11370. These four prototypes began their test evaluation on October 10, 1972 at Edwards AFB, CA for the USAF A-X Joint Test Force. The flight tests were to comprise 250 total hours for both models by 5 USAF TAC and Air Force Systems Command pilots over a two month period. These pilots had earlier knowledge and experience with these models to insure both fairness and full performance testing. The competing designs were flown in pairs for the trials to insure no variation in external temperature, wind or environmental factors. Prototypes were alternated for each company, and the pilots were alternated between aircraft models, in addition to alternating lead and wing positions.
Northrop YA-9: The Other Bird
Northrop maintains a long history of producing rugged and survivable aircraft, and its YA-9 design represented a more conventional design, with twin Avco-Lycoming YF102-LD- 100 turbofans (7,500 lbs thrust) mounted in fairings at the wing roots, landing gear that fully retracted, a single vertical stabilizer, and five pylon hardpoint locations on each straight shouldered wing.
Fairchild YA-10: What the Hell is That?
Fairchild (Republic)’s design represented a fundamental emphasis on survivability and redundancy at the expense of conventional design esthetics... plain and simple, this was the bird from hell. With straight wings and twin vertical tails, and twin General Electric TF34-100 turbofans (9,065 lbs thrust) mounted on fuselage pylons aft of the wings [the engines are also used on the S-3A Viking], eleven total hardpoints, and landing gear that partially retracted, the YA-10 easily could be distinguished from the YA-9.
The Competition: Fly Before You Buy
The tests in store for these four prototypes were strenuous, and sought to assess the performance of each design. The basic tasks and tests are described below:
Performance testing 50 hours
System checks 6 hours
Weapons delivery 54 hours
TAC mission suitability 20 hours
Recordings taken for all aircraft included full working cockpit instrumention with data readouts; radar tracking of weapons delivery (bomb and strafing runs); ground surveys of bomb tests for weapons delivery accuracy. Although 250 total hours were initially planned for evaluation, 328 hours were finally recorded on the YA-10s, and 307 hours on the YA-9s prototypes.
The Competition: Results
The test evaluations were completed on December 9, 1972, and on January 18, 1973, a contract was awarded to Fairchild Republic for an additional 10 aircraft for further research and development as winner of the A-X competition. The number of additional aircraft were later revised to include 8 Design Test and Evaluation (DT&E) airframes, 6 flight evaluation airframes, one static testing airframe, and one airframe for fatigue tests. A $159.2 million dollar contract was signed on March 1, 1973 for the airframes, and a simultaneous contract was signed with GE for the TF34 turbofan engines.
Factors that favored the Fairchild design over the Northrop proposal included the ease of access to underwing hardpoints, ease of engine maintenance, and the perceived easier path from prototype tooling to production airframe (given the high structural polish of the Fairchild prototypes). Higher flight hour-to-maintenance hour ratios, and the high level of redundancy within the design were additional factors. Yet the decision for selection of the YA-10 was not a foregone conclusion, as the Northrop design had superior handling characteristics and a unique side-force control system, linking speed brakes and the rudder. This yaw manueverability provided a level of ground target tracking independent of bank angle or fuselage axis direction.
