Fairchild Republic A-10 Thunderbolt II

The Fairchild Republic A-10 Thunderbolt II is an American single-seat, twin-engine, straight-wing jet aircraft developed by Fairchild-Republic in the early 1970s. The only United States Air Force aircraft designed solely for close air support of ground forces, the A-10 was built to attack tanks, armored vehicles, and other ground targets with limited air defenses. It also has a secondary mission, where it provides airborne forward air control, guiding other aircraft against ground targets. Aircraft used primarily in this role are designated OA-10. With a variety of upgrades and wing replacements, the A-10's service life has been extended to 2040.

The A-10 was designed around the GAU-8 Avenger, a rotary cannon that is the airplane's primary armament and the heaviest such cannon mounted on an aircraft. The A-10's airframe was designed for survivability, with protective measures such as 1,200 pounds (540 kg) of armor to enable the aircraft to continue flying after taking damage. The A-10's official name comes from the Republic P-47 Thunderbolt of World War II, a fighter that was particularly effective at close air support. The A-10 is more commonly known by its nicknames "Warthog" or "Hog".

Role Fixed-wing close air support, forward air control, and ground-attack aircraft
Manufacturer Fairchild Republic
First flight 10 May 1972
Introduction March 1977
Status In service
Primary user United States Air Force
Produced 1972–1984
Number built 716
Unit cost US$11.8 million (average, 1994 dollars)

Design

Overview

Side-view drawing of aircraft with cut throughs showing crucial internal components
A-10 inboard profile drawing

The A-10 has superior maneuverability at low speeds and altitude because of its large wing area, high wing aspect ratio, and large ailerons. The high aspect ratio wing also allows for short takeoffs and landings, permitting operations from primitive forward airfields near front lines. The aircraft can loiter for extended periods and operate under 1,000 ft (300 m) ceilings with 1.5 mi (2.4 km) visibility. It typically flies at a relatively slow speed of 300 knots (350 mph; 560 km/h), which makes it a much better platform for the ground-attack role than fast fighter-bombers, which often have difficulty targeting small and slow-moving targets.

Engine exhaust passes over the aircraft's horizontal stabilizer and between the twin tails, decreasing the A-10's infrared signature and lowering the likelihood that the aircraft can be targeted by heat-seeking missiles fired from the ground. The placement of the engines behind the wings partially shields them from anti-aircraft fire. The leading edge of the wing is honeycomb panel construction to provide strength with minimal weight compromise. Honeycomb panels of this type on the A-10 include the flap shrouds, elevators, rudders and other sections of the fins.

An A-10A of pre-glass cockpit design

The A-10 has integrally machined skin panels. Because the stringers are integral with the skin, there are no joint or seal problems. These panels, fabricated using computer controlled machining, reduce the time and hence the cost of production. Combat experience has shown that this type of panel is more resistant to damage. The skin is not load-bearing, so damaged skin sections can be easily replaced in the field, with makeshift materials if necessary.

The ailerons are at the far ends of the wings to gain greater rolling moment, as with many aircraft, but there are two distinguishing features. The ailerons are larger than is typical, almost 50% of the wingspan, providing improved control even at slow speeds. The aileron is also split, making it a deceleron.

The A-10 is designed to be refueled, rearmed, and serviced with minimal equipment. Also, most repairs can be done in the field. An unusual feature is that many of the aircraft's parts are interchangeable between the left and right sides, including the engines, main landing gear, and vertical stabilizers. The sturdy landing gear, low-pressure tires and large, straight wings allow operation from short rough strips even with a heavy ordnance load, allowing the aircraft to operate from damaged airbases. If runways are damaged in an attack, the A-10 can operate from taxiways or straight roadway sections.

Front view of an A-10 showing the 30 mm cannon and offset front landing gear

The front landing gear is offset to the aircraft's right to allow placement of the 30 mm cannon with its firing barrel along the centerline of the aircraft. During ground taxi, the offset front landing gear causes the A-10 to have dissimilar turning radii. Turning to the right on the ground takes less distance than turning left.

Durability

The A-10 is exceptionally tough. Its strong airframe can survive direct hits from armor-piercing and high-explosive projectiles up to 23 mm. The aircraft has triple redundancy in its flight systems, with mechanical systems to back up double-redundant hydraulic systems. This permits pilots to fly and land when hydraulic power or part of a wing is lost. Flight without hydraulic power uses the manual reversion flight control system; this engages automatically for pitch and yaw control, and under pilot control (manual reversion switch) for roll control. In manual reversion mode, the A-10 is sufficiently controllable under favorable conditions to return to base and land, though control forces are much higher than normal. The aircraft is designed to fly with one engine, one tail, one elevator, and half of one wing missing.

Its self-sealing fuel tanks are protected by fire-retardant foam. The A-10's main landing gear is designed so that the wheels partially protrude from their nacelles when the gear is retracted so as to make gear-up belly landings easier to control and less damaging to the aircraft's underside. Additionally, the landing gears are all hinged toward the rear of the aircraft, so if hydraulic power is lost the pilot can drop the gear and a combination of gravity and wind resistance will open and lock the gear in place.

The cockpit and parts of the flight-control system are protected by 1,200 lb (540 kg) of titanium armor, referred to as a "bathtub". The armor has been tested to withstand strikes from 23 mm cannon fire and some strikes from 57 mm rounds. It is made up of titanium plates with thicknesses from 0.5 to 1.5 inches (13 to 38 mm) determined by a study of likely trajectories and deflection angles. This protection comes at a cost, with the armor making up almost 6% of the aircraft's empty weight. To protect the pilot from the fragmentation likely to be created from impact of a shell, any interior surface of the tub that is directly exposed to the pilot is covered by a multi-layer nylon spall shield. In addition, the front windscreen and canopy are resistant to small arms fire.

This A-10 Thunderbolt II suffered extensive damage over Baghdad during Operation Iraqi Freedom in early 2003. It successfully returned to base.

Proof of the durability of the A-10 was shown when Captain Kim Campbell, flying a ground support mission over Baghdad during the 2003 invasion of Iraq on 7 April, suffered extensive flak damage to her A-10. Iraqi fire damaged one of the A-10's engines and crippled its hydraulic system, which required the aircraft's stabilizer and flight controls to be operated via the back-up mechanical system, this being known as 'manual reversion mode'. Despite this damage, Campbell managed to fly the aircraft for nearly an hour and landed safely.

There are several reasons for the unusual location of the A-10's General Electric TF34-GE-100 turbofan engines. First, the A-10 was envisioned to fly from forward air bases, often with substandard, semi-prepared runways that present a high risk of foreign object damage to the engines. The height of the engines decreases the chance that sand or stones will be ingested. This also allows engines to keep running while the aircraft is serviced and rearmed by ground crews, reducing turn-around time. Without the limitations imposed by engines, the wings could be mounted closer to the ground, to simplify servicing and rearming.

USAF Thunderbolt taxiing, showing high-mounted engines

The engines' high 6:1 bypass ratio provides the A-10 with a relatively small infrared signature, and their position directs exhaust over the tailplanes further shielding it from detection by heat-seeking surface to air missiles. The engines are angled upward by nine degrees to cancel out the nose-down pitching moment they would otherwise generate due to being mounted above the aerodynamic center of the aircraft. This avoids the necessity to trim the control surfaces against the force. The heavy engines require strong supports, so their pylons are connected to the airframe by four bolts.

The A-10's fuel system components are protected in multiple ways. All four fuel tanks are located near the center of the aircraft, reducing the likelihood that they will be hit or have their fuel lines severed. The tanks are separate from the fuselage; thus, projectiles would need to penetrate the aircraft's skin before reaching the outer skin of the tank. The refueling system is purged after use so that all fuel in the aircraft is protected from fire. All fuel transfer lines self-seal if they are compromised; if a tank is damaged beyond its ability to self-seal, check valves prevent fuel flowing into the compromised tank. Most of the fuel system components are inside the tanks so that fuel will not be lost in case a component were to leak. Most importantly, reticulated polyurethane foam lines both the inner and outer sides of the fuel tanks, retaining debris and restricting fuel spillage in the event of damage. The other source of possible combustion, the engines, are shielded from the fuel system and the rest of the airframe by firewalls and fire extinguishing equipment. Even in the event of all four main tanks being penetrated and all contents lost, sufficient fuel is carried in two self-sealing sump tanks to allow flight for 230 miles (370 km).

Weapons

A side-view drawing of the A-10's GAU-8/A Avenger gun and its approximate location in the fuselage

Although the A-10 can carry considerable disposable stores, its primary built-in weapon is the 30 mm GAU-8/A Avenger Gatling-type cannon. One of the most powerful aircraft cannons ever flown, it fires large depleted uranium armor-piercing shells. In the original design, the pilot could switch between two rates of fire: 2,100 or 4,200 rounds per minute; this was changed to a fixed rate of 3,900 rounds per minute. The cannon takes about half a second to come up to speed, so 50 rounds are fired during the first second, 65 or 70 rounds per second thereafter. The gun is accurate enough to place 80% of its shots within a 40-foot (12.4 m) diameter circle from 4,000 feet (1,220 m) while in flight. The GAU-8 is optimized for a slant range of 4,000 feet (1,220 m) with the A-10 in a 30 degree dive.

Another view of the A-10's GAU-8 installation

The fuselage of the aircraft is built around the cannon. The GAU-8/A is mounted slightly to the port side; the barrel in the firing location is on the starboard side at the 9 o'clock position so it is aligned with the aircraft's centerline. The gun's 5-foot, 11.5-inch (1.816 m) ammunition drum can hold up to 1,350 rounds of 30 mm ammunition, but generally holds 1,174 rounds. To prevent enemy shells from causing the GAU-8/A rounds to fire prematurely, armor plates of differing thicknesses between the aircraft skin and the drum are designed to detonate incoming shells. A final layer of armor around the drum protects it from fragmentation damage. The gun is loaded by Syn-Tech's linked tube carrier GFU-7/E 30 mm ammunition loading assembly cart.

Another commonly used weapon is the AGM-65 Maverick air-to-surface missile, with variants for electro-optical (TV-guided) or infrared targeting. The Maverick allows targets to be engaged at much greater ranges than the cannon, a safer proposition in the face of modern anti-aircraft systems. During Desert Storm, in the absence of dedicated forward-looking infrared (FLIR) cameras for night vision, the Maverick's infrared camera was used for night missions as a "poor man's FLIR". Other weapons include cluster bombs and Hydra rocket pods. Although the A-10 is equipped to carry laser-guided bombs, their use is relatively uncommon. As of 2000, the A-10 has not been equipped with weapon control systems for accurate bombing. A-10s usually fly with an ALQ-131 ECM pod under one wing and two AIM-9 Sidewinder air-to-air missiles under the other wing for self-defense.

Aircraft in-flight above clouds, banking away from camera, revealing bombs and other weapons suspended underneath wings.
A-10 Thunderbolt II, fully armed

Modernization

The A-10 Precision Engagement Modification Program will update 356 A-10/OA-10s to the A-10C variant with a new flight computer, new glass cockpit displays and controls, two new 5.5-inch (140 mm) color displays with moving map function and an integrated digital stores management system.

Other funded improvements to the A-10 fleet include a new data link, the ability to employ smart weapons such as the Joint Direct Attack Munition("JDAM") and Wind Corrected Munitions Dispenser, and the ability to carry an integrated targeting pod such as the Northrop Grumman LITENING targeting pod or the Lockheed Martin Sniper XR Advanced Targeting Pod (ATP). Also included is the Remotely Operated Video Enhanced Receiver (ROVER) to provide sensor data to personnel on the ground.

Colors and markings

Since the A-10 flies low to the ground and at subsonic speed, aircraft camouflage is important to make the aircraft more difficult to see. Many different types of paint schemes have been tried. These have included a "peanut scheme" of sand, yellow and field drab; black and white colors for winter operations and a tan, green and brown mixed pattern.

The two most common markings applied to the A-10 have been the European I woodland camouflage scheme and a two-tone gray scheme. The European woodland scheme was designed to minimize visibility from above, as the threat from hostile fighter aircraft was felt to outweigh that from ground-fire. It uses dark green, medium green and dark gray in order to blend in with the typical European forest terrain and was used from the 1980s to the early 1990s. Following the end of the Cold War, and based on experience during the 1991 Gulf War, the air-to-air threat was no longer seen to be as important as that from ground fire, and a new color scheme known as "Compass Ghost" was chosen to minimize visibility from below. This two-tone gray scheme has darker gray color on top, with the lighter gray on the underside of the aircraft, and started to be applied from the early 1990s.

Many A-10s also featured a false canopy painted in dark gray on the underside of the aircraft, just behind the gun. This form of automimicry is an attempt to confuse the enemy as to aircraft attitude and maneuver direction. Many A-10s feature nose art, such as shark mouth or warthog head features.

Operators

An A-10 Thunderbolt II banks left after refueling

The A-10 has been flown exclusively by the United States Air Force and its Air Reserve components, the Air Force Reserve Command (AFRC) and the Air National Guard (ANG). The USAF operated 345 A-10 and OA-10 aircraft (191 in active duty, 106 in ANG, and 48 in AFRC, all variants) as of September 2011.

The Air Force operates multiple A-10/OA-10 Active, Air Force Reserve and Air National Guard wings and squadrons.

United States Air Force
  • 23d Wing: Moody Air Force Base, Georgia
    • 74th Fighter Squadron
    • 75th Fighter Squadron
  • 51st Fighter Wing: Osan Air Base, South Korea
    • 25th Fighter Squadron
  • 52d Fighter Wing: Spangdahlem Air Base, Germany
    • 81st Fighter Squadron (squadron inactivation scheduled for FY 2013)
  • 53d Wing: Eglin Air Force Base, Florida
    • 422d Test and Evaluation Squadron (Geographically Separated Unit at Nellis Air Force Base, Nevada)
  • 57th Wing: Nellis Air Force Base, Nevada
    • 66th Weapons Squadron
  • 355th Wing: Davis-Monthan Air Force Base, Arizona
    • 354th Fighter Squadron
    • 357th Fighter Squadron
    • 358th Fighter Squadron
Four A-10s of the 111th Fighter Wing,Pennsylvania Air National Guard, fly in formation during a refueling mission.
Air National Guard
  • 127th Wing at Selfridge ANGB, Michigan (Transitioned from F-16s to A-10s due to BRAC 2005)
    • 107th Fighter Squadron
  • 122nd Fighter Wing (formerly 358th Fighter Group): Fort Wayne, Indiana
    • 163d Fighter Squadron
  • 124th Fighter Wing: Boise Air Terminal, Idaho
    • 190th Fighter Squadron
  • 175th Wing: Warfield ANGB, Martin State Airport, Maryland
    • 104th Fighter Squadron
  • 188th Fighter Wing: Fort Smith, Arkansas (Transitioned from F-16s to A-10s due to BRAC 2005)
    • 184th Fighter Squadron
Air Force Reserve Command
  • 442d Fighter Wing: Whiteman Air Force Base, Missouri
    • 442d Operations Group
      • 303d Fighter Squadron
    • 476th Fighter Group (Geographically Separated Unit (GSU) of 442 FW at Moody AFB, Georgia)
      • 76th Fighter Squadron (GSU at Moody AFB, Georgia)
    • 917th Fighter Group: (GSU of 442 FW at Barksdale AFB, Louisiana)
      • 47th Fighter Squadron
  • 944th Fighter Wing: Luke AFB, Arizona
    • 924th Fighter Group (GSU of 944 FW at Davis-Monthan AFB, Arizona)
      • 45th Fighter Squadron (GSU of 944 FW at Davis-Monthan AFB, Arizona)

 

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