Fairchild Republic A-10 Thunderbolt II
The Fairchild Republic A-10 , also widely known by the nickname Warthog, is a single-seat, twin-turbofan, straight-wing, subsonic attack aircraft developed by Fairchild Republic for the United States Air Force. In service since 1977, it is named after the Republic P-47 Thunderbolt strike-fighter of World War II, but is instead commonly referred to as the "Warthog". The A-10 was designed to provide close air support to ground troops by attacking enemy armored vehicles, tanks, and other ground forces; it is the only production-built aircraft designed solely for CAS to have served with the U.S. Air Force. Its secondary mission is to direct other aircraft in attacks on ground targets, a role called forward air controller -airborne; aircraft used primarily in this role are designated OA-10.
The A-10 was intended to improve on the performance and firepower of the Douglas A-1 Skyraider. The Thunderbolt II's airframe was designed around the high-power 30 mm GAU-8 Avenger rotary autocannon. The airframe was designed for durability, with measures such as of titanium armor to protect the cockpit and aircraft systems, enabling it to absorb damage and continue flying. Its ability to take off and land from relatively short and unpaved runways permits operation from airstrips close to the front lines, and its simple design enables maintenance with minimal facilities.
It served in the Gulf War, the American-led intervention against Iraq's invasion of Kuwait, where the aircraft distinguished itself. The A-10 also participated in other conflicts such as the Balkans, Afghanistan, the Iraq War, and against the Islamic State in the Middle East.
The A-10A single-seat variant was the only version produced, though one pre-production airframe was modified into the YA-10B twin-seat prototype to test an all-weather night-capable version. In 2005, a program was started to upgrade the remaining A-10A aircraft to the A-10C configuration, with modern avionics for use with precision weaponry. The U.S. Air Force had stated the Lockheed Martin F-35 Lightning II would replace the A-10 as it entered service, but this remains highly contentious within the USAF and in political circles. The USAF gained congressional permission to start retiring A-10s in 2023, but further retirements were paused until the USAF can demonstrate that the A-10's close-air-support capabilities can be replaced.
Development
Background
The development of conventionally armed attack aircraft in the United States stagnated after World War II, as design efforts for tactical aircraft focused on the delivery of nuclear weapons using high-speed designs such as the McDonnell F-101 Voodoo and Republic F-105 Thunderchief. As the U.S. military entered the Vietnam War, its main ground-attack aircraft was the Korean War-era Douglas A-1 Skyraider. A capable aircraft for its era, with a relatively large payload and long loiter time, the propeller-driven design had become relatively slow, vulnerable, particularly to ground fire, and incapable of providing adequate firepower. The U.S. Air Force and Navy lost some 266 A-1s in action in Vietnam, largely from small-arms fire.The lack of modern conventional attack capability prompted calls for a specialized attack aircraft. On 7 June 1961, the Secretary of Defense Robert McNamara ordered the USAF to develop two tactical aircraft, one for the long-range strike and interdictor role, and the other focusing on the fighter-bomber mission. The former was the Tactical Fighter Experimental intended to be a common design for the USAF and the US Navy, which emerged as the General Dynamics F-111 Aardvark, while the second was filled by a version of the U.S. Navy's McDonnell Douglas F-4 Phantom II. While the Phantom went on to be one of the most successful fighter designs of the 1960s and proved to be a capable fighter-bomber, its short loiter time was a major problem, as was its poor low-speed performance, albeit to a lesser extent. It was also expensive to buy and operate, with a flyaway cost of $2 million in FY1965, and operational costs over $900 per hour.
After a broad review of its tactical force structure, the USAF decided to adopt a low-cost aircraft to supplement the F-4 and F-111. It first focused on the Northrop F-5, which had air-to-air capability. A 1965 cost-effectiveness study shifted the focus from the F-5 to the less expensive A-7D variant of the LTV A-7 Corsair II, and a contract was awarded. However, this aircraft doubled in cost with demands for an upgraded engine and new avionics.
Army helicopter competition
During this period, the United States Army had been introducing the Bell UH-1 Iroquois into service. First used in its intended role as a transport, it was soon modified in the field to carry more machine guns in what became known as the helicopter gunship role. This proved effective against the lightly armed enemy, and new gun and rocket pods were added. Soon the Bell AH-1 Cobra was introduced. This was an attack helicopter armed with long-range BGM-71 TOW missiles able to destroy tanks from outside the range of defensive fire. The helicopter was effective and prompted the U.S. military to change its defensive strategy in Europe into blunting any Warsaw Pact advance with anti-tank helicopters instead of the tactical nuclear weapons that had been the basis for NATO's battle plans since the 1950s.The Cobra was a quickly-made helicopter based on the UH-1 Iroquois and was introduced in the mid-1960s as an interim design until the U.S. Army's "Advanced Aerial Fire Support System" helicopter could be delivered. The Army selected the Lockheed AH-56 Cheyenne, a more capable attack aircraft with greater speed for initial production. The development of the anti-tank helicopter concerned the USAF; a 1966 USAF study of existing close air support capabilities revealed gaps in the escort and fire suppression roles that the Cheyenne could fill. The study concluded that the service should acquire a simple, inexpensive, dedicated CAS aircraft at least as capable as the A-1, and that it should develop doctrine, tactics, and procedures for such aircraft to accomplish the missions for which the attack helicopters were provided.
A-X program
On 8 September 1966, General John P. McConnell, Chief of Staff of the USAF, ordered that a specialized CAS aircraft be designed, developed, and obtained. On 22 December, a Requirements Action Directive was issued for the A-X CAS airplane, and the Attack Experimental program office was formed. On 6 March 1967, the USAF released a request for information to 21 defense contractors for the A-X.In May 1970, the USAF issued a modified, more detailed request for proposals for the aircraft. The threat of Soviet armored forces and all-weather attack operations had become more serious. The requirements now included that the aircraft would be designed specifically for the 30 mm rotary cannon. The RFP also specified a maximum speed of, takeoff distance of, external load of, mission radius, and a unit cost of US$1.4 million. The A-X would be the first USAF aircraft designed exclusively for CAS. During this time, a separate RFP was released for A-X's 30 mm cannon with requirements for a high rate of fire and a high muzzle velocity. Six companies submitted aircraft proposals, with Northrop and Fairchild Republic in Germantown, Maryland, selected to build prototypes: the YA-9A and YA-10A, respectively. General Electric and Philco-Ford were selected to build and test GAU-8 cannon prototypes.
Two YA-10 prototypes were built in the Republic factory in Farmingdale, New York, and first flown on 10 May 1972 by pilot Howard "Sam" Nelson. Production A-10s were built by Fairchild in Hagerstown, Maryland. After trials and a fly-off against the YA-9, on 18 January 1973, the USAF announced the YA-10's selection for production. General Electric was selected to build the GAU-8 cannon in June 1973. The YA-10 had an additional fly-off in 1974 against the Ling-Temco-Vought A-7D Corsair II, the principal USAF attack aircraft at the time, to prove the need for a new attack aircraft. The first production A-10 flew in October 1975, and deliveries commenced in March 1976.
One experimental two-seat A-10 Night Adverse Weather version was built by Fairchild by converting the first Demonstration Testing and Evaluation A-10A for consideration by the USAF. It included a second seat for a weapon systems officer responsible for electronic countermeasures, navigation and target acquisition. The N/AW version did not interest the USAF or export customers. The two-seat trainer version was ordered by the USAF in 1981, but funding was canceled by U.S. Congress and was not produced. The only two-seat A-10 resides at Edwards Air Force Base's Flight Test Center Museum.
Production
On 10 February 1976, Deputy Secretary of Defense Bill Clements authorized full-rate production while the first A-10 was accepted by the USAF Tactical Air Command on 30 March 1976. Production continued and reached a peak rate of 13 aircraft per month. By 1984, 715 airplanes, including 2 prototypes and 6 development aircraft, had been delivered.When full-rate production was first authorized, the A-10's planned service life was 6,000 hours. A small design reinforcement was quickly adopted when initial fatigue testing failed at 80% of testing; the A-10 passed fatigue tests with the fix. 8,000-flight-hour service lives were becoming common at the time, so fatigue testing of the A-10 continued with a new 8,000-hour target. This new target quickly discovered serious cracks at Wing Station 23 where the outboard portions of the wings are joined to the fuselage. The first production change was to address this problem by adding cold working at WS23. Soon after, the USAF found that the real-world A-10 fleet fatigue was harsher than estimated, forcing a change to fatigue testing and introduced "spectrum 3" equivalent flight-hour testing.
Spectrum 3 fatigue testing started in 1979. This round of testing quickly determined that more drastic reinforcement would be needed. The second change in production, starting with aircraft No. 442, was to increase the thickness of the lower skin on the outer wing panels. A tech order was issued to retrofit the "thick skin" to the whole fleet, but the tech order was rescinded after roughly 242 planes, leaving about 200 planes with the original "thin skin". Starting with aircraft No. 530, cold working at WS0 was performed, and this retrofit was performed on earlier aircraft. A fourth, even more drastic change was initiated with aircraft No. 582, again to address the problems discovered with spectrum 3 testing. This change increased the thickness of the lower skin on the center wing panel, but it required modifications to the lower spar caps to accommodate the thicker skin. The USAF found it economically unfeasible to retrofit earlier planes with this modification.