The
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable en ...
GAU-8/A Avenger is a
30 mm
30 mm caliber is a specific size of popular autocannon ammunition. Such ammunition includes NATO standard 30×113mmB and 30×173mm (STANAG 4624), Soviet 30×155mmB, 30×165mm, and 30×210mmB, Yugoslav 30×192mm, Anglo-Swiss 30×170mm, an ...
hydraulically driven seven-barrel
Gatling-style autocannon that is primarily mounted in the
United States Air Force
The United States Air Force (USAF) is the Aerial warfare, air military branch, service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part ...
's
Fairchild Republic A-10 Thunderbolt II. Designed to destroy a wide variety of ground targets, the Avenger delivers very powerful rounds at a high
rate of fire. The GAU-8/A is also used in the
Goalkeeper CIWS
The Goalkeeper CIWS is a Dutch close-in weapon system (''SEE-wiz'') introduced in 1979. It is an autonomous and completely automatic weapon system for short-range defence of ships against highly manoeuvrable missiles, aircraft and fast-manoeuve ...
ship weapon system, which provides defense against short-range threats such as highly maneuverable missiles, aircraft, and fast maneuvering surface vessels. The GAU-8/A is currently produced by
General Dynamics.
History
The GAU-8 was created as a parallel program with the ''A-X'' (or Attack Experimental) competition that produced the A-10. The specification for the cannon was laid out in 1970,
with
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable en ...
and
Philco-Ford
Philco (an acronym for Philadelphia Battery Company) is an American electronics manufacturer headquartered in Philadelphia. Philco was a pioneer in battery, radio, and television production. In 1961, the company was purchased by Ford and, from 196 ...
offering competing designs. Both of the A-X prototypes, the
YA-10 and the
Northrop YA-9
The Northrop YA-9 was a prototype attack aircraft developed for the United States Air Force A-X program. The YA-9 was passed over in preference for the Fairchild Republic YA-10 that entered production as the A-10 Thunderbolt II.
Design and de ...
, were designed to incorporate the weapon, although it was not available during the initial competition; the
M61 Vulcan
The M61 Vulcan is a hydraulically, electrically, or pneumatically driven, six- barrel, air-cooled, electrically fired Gatling-style rotary cannon which fires rounds at an extremely high rate (typically 6,000 rounds per minute). The M61 and i ...
was used as a temporary replacement. Once completed, the entire GAU-8 assembly (correctly referred to as the A/A 49E-6 Gun System)
represents about 16% of the A-10 aircraft's unladen weight. Because the gun plays a significant role in maintaining the A-10's balance and center of gravity, a jack must be installed beneath the airplane's tail whenever the gun is removed for inspection in order to prevent the aircraft from tipping rearwards.
The gun is mounted slightly to the port side with the active firing cannon barrel on the starboard side at the 9 o'clock position and on the aircraft's center line. The front
landing gear
Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Martin ...
is positioned to the starboard side.
[Donald, David and Daniel J. March, eds. "A-10 Fighting Warthog", p. 20. ''Modern Battlefield Warplanes''. Norwalk, Connecticut: AIRtime, 2004. .] The gun is loaded using Syn-Tech's linked tube carrier GFU-8/E 30 mm Ammunition Loading Assembly cart. This vehicle is unique to the A-10 and the GAU-8.
The A-10 with its GAU-8/A gun entered service in 1977. It was produced by
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable en ...
, though
General Dynamics Armament and Technical Products has been responsible for production and support since 1997 when the division was sold by
Lockheed Martin to
General Dynamics.
Design
The GAU-8 itself weighs , but the complete weapon, with feed system and drum, weighs with a maximum ammunition load. It measures from the muzzle to the rearmost point of the ammunition system, and the ammunition drum alone is in diameter and long.
[Spick 2000, p. 44.] Power for operating the gun is provided by twin
hydraulic motor
A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadly, ...
s pressurized from two independent hydraulic systems. The magazine can hold 1,174 rounds, although 1,150 is the typical load-out. Muzzle velocity when firing armor-piercing incendiary rounds is 1,013 m/s, almost the same as the substantially lighter M61 Vulcan's 20 mm round, giving the gun a
muzzle energy
Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. Without consideration of factors such as aerodynamics and gravity for the sake of comparison, muzzle energy is used as a rough indication of the de ...
of just over 200
kilojoules
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
.
The standard ammunition mixture for anti-armor use is a five-to-one mix of PGU-14/B
Armor Piercing
Armour-piercing ammunition (AP) is a type of projectile designed to penetrate either body armour or vehicle armour.
From the 1860s to 1950s, a major application of armour-piercing projectiles was to defeat the thick armour carried on many warsh ...
Incendiary, with a projectile weight of about 14.0 oz (395 grams or 6,096 grains) and PGU-13/B
High Explosive Incendiary
In warfare, high-explosive incendiary (HEI) is a type of ammunition specially designed to impart energy and therefore damage to its target in one or both of two ways: via a high-explosive charge and/or via its incendiary (fire-causing) effects. ...
(HEI) rounds, with a projectile weight of about 13.3 oz (378 grams or 5,833 grains). The PGU-14/B's projectile incorporates a lightweight aluminum body, cast around a smaller caliber
depleted uranium penetrating core.
In 1979, the Avenger was tested against M47 Patton tanks and caused "severe damage".
An innovation in the design of the GAU-8/A ammunition is the use of aluminum alloy cases in place of the traditional steel or brass.
[ This alone adds 30% to ammunition capacity for a given weight. The projectiles incorporate a plastic ]driving band Russian 122 mm shrapnel shell, which has been fired, showing rifling marks on the copper driving band around its base and the steel bourrelet nearer the front
A driving band or rotating band is a band of soft metal near the base of an artillery ...
to improve barrel life. The cartridges measure in length and weigh or more.[
The Avenger's rate of fire was originally selectable, 2,100 rounds per minute (rpm) in the low setting, or 4,200 rpm in the high setting.] This rate was later changed to a fixed rate of 3,900 rpm. At this speed it would take 18 seconds of sustained fire to empty the magazine. In practice, the cannon is limited to one and two-second bursts to avoid overheating and conserve ammunition; barrel life is also a factor, since the USAF has specified a minimum life of at least 20,000 rounds for each set of barrels.[ There is no technical limitation on the duration the gun may be continuously fired, and a pilot could potentially expend the entire ammunition load in a single burst with no damage or ill effects to the weapons system itself. However, this constant rate of fire would shorten the barrel life considerably and require added barrel inspections and result in shorter intervals between replacement.
Each barrel is a very simple non-automatic design having its own ]breech
Breech may refer to:
* Breech (firearms), the opening at the rear of a gun barrel where the cartridge is inserted in a breech-loading weapon
* breech, the lower part of a pulley block
* breech, the penetration of a boiler where exhaust gases leav ...
and bolt. Like the original Gatling gun, the entire firing cycle is actuated by cam
Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...
s and powered by the rotation of the barrels. The seven-barrel carriage assembly itself is driven by the aircraft's dual hydraulic system.
The GAU-8/A ammunition feed is linkless, reducing weight and avoiding a great deal of potential for jamming. The feed system is double-ended, allowing the spent casings to be returned to the ammunition drum. Additionally, returning empty cases to the drum has less effect on the aircraft's center of gravity than ejecting them. The feed system is based on that developed for later M61 installations, but uses more advanced design techniques and materials throughout, to save weight.[
]
Firing system
Accuracy
The GAU-8/A is extremely accurate and can fire up to 3,900 rounds per minute without complications. The 30-mm shell has twice the range, half the time to target, and three times the mass of projectiles fired by guns mounted in comparable close air support aircraft.
The muzzle velocity of the GAU-8/A is about the same as that of the M61 Vulcan
The M61 Vulcan is a hydraulically, electrically, or pneumatically driven, six- barrel, air-cooled, electrically fired Gatling-style rotary cannon which fires rounds at an extremely high rate (typically 6,000 rounds per minute). The M61 and i ...
cannon, but the GAU-8/A uses heavier ammunition and has superior ballistics. The time of flight of its projectile to is 30 percent less than that of an M61 round; the GAU-8/A projectile decelerates much less after leaving the barrel, and it drops a negligible amount, about over the distance.[Jenkins 1998, pp. 64–73.] The GAU-8/A accuracy when installed in the A-10 is rated at "5 mil, 80 percent", meaning that 80 percent of rounds fired will hit within a cone with an angle of five milliradian
A milliradian ( SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of firearm sights by adjusting t ...
s; this equates to a diameter circle at the weapon's design range of . By comparison, the M61 has an 8-milliradian dispersion.[
]
Recoil
Because the gun's recoil
Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, as according to Newton's third law the force r ...
forces could push the entire plane off target during firing, the weapon is mounted laterally off-center, slightly to the port side of the fuselage
The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraf ...
centerline, with the active firing barrel lying directly on the aircraft's centerline.[ The firing barrel also lies just below the aircraft's center of gravity, being bore-sighted along a line 2 degrees below the aircraft's line of flight. This arrangement accurately centers the recoil forces, preventing changes in aircraft pitch or yaw when fired. This configuration also leaves space for the front landing gear, which is mounted slightly off-center on the starboard side of the nose.]
The GAU-8/A utilizes recoil adapters. They are the interface between the gun housing and the gun mount. By absorbing (in compression) the recoil forces, they spread the time of the recoil impulse and counter recoil energy transmitted to the supporting structure when the gun is fired.
The A-10 engines were initially susceptible to flameout
In aviation, a flameout (or flame-out) is the run-down of a jet engine or other turbine engine due to the extinction of the flame in its combustor. The loss of flame can have a variety of causes, such as fuel starvation, excessive altitude, com ...
when subjected to gases generated in the firing of the gun. When the GAU-8 is being fired, the smoke from the gun can make the engines stop, and this did occur during initial flight testing.[ Gun exhaust is essentially oxygen-free, and is certainly capable of causing flameouts of ]gas turbine
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...
s. The A-10 engines now have a self-sustaining combustion section. When the gun is fired, the igniters come on to reduce the possibility of a flameout.
The average recoil force of the GAU-8/A is 10,000 pounds-force
The pound of force or pound-force (symbol: lbf, sometimes lbf,) is a unit of force used in some systems of measurement, including English Engineering units and the foot–pound–second system.
Pound-force should not be confused with pound-ma ...
(45 kN),[ which is slightly more than the output of each of the A-10's two ]TF34
The General Electric TF34 is an American military turbofan engine used on the A-10 Thunderbolt II and S-3 Viking.
Design and development
Developed by GE Aircraft Engines during the late 1960s, the original engine comprises a single stage fan, ...
engines of 9,065 lbf (40.3 kN). While this recoil force is significant, in practice a cannon-fire burst slows the aircraft by only a few miles per hour in level flight.[
]
Variants
Some of the GAU-8/A technology has been transferred into the smaller 25 mm GAU-12/U Equalizer, which was developed for the AV-8B Harrier II
The McDonnell Douglas (now Boeing) AV-8B Harrier II is a single-engine ground-attack aircraft that constitutes the second generation of the Harrier family, capable of vertical or short takeoff and landing (V/STOL). The aircraft is primari ...
aircraft. The GAU-12 is about the same size as the 20 mm M61. GE has also developed the GAU-13/A, a four-barreled weapon using GAU-8/A components, which has been tested in podded form as the GPU-5/A. The Avenger also forms the basis for the Dutch-developed Goalkeeper CIWS
The Goalkeeper CIWS is a Dutch close-in weapon system (''SEE-wiz'') introduced in 1979. It is an autonomous and completely automatic weapon system for short-range defence of ships against highly manoeuvrable missiles, aircraft and fast-manoeuve ...
naval air-defence gun. No current or contemplated aircraft other than the A-10 carries the full-up Avenger system.[
]
Specifications
* Precision: 80% of rounds fired at range hit within a diameter circle.
* Ammo:
** PGU-14/B API Armor Piercing
Armour-piercing ammunition (AP) is a type of projectile designed to penetrate either body armour or vehicle armour.
From the 1860s to 1950s, a major application of armour-piercing projectiles was to defeat the thick armour carried on many warsh ...
Incendiary ( DU)
** PGU-13/B HEI High explosive incendiary
In warfare, high-explosive incendiary (HEI) is a type of ammunition specially designed to impart energy and therefore damage to its target in one or both of two ways: via a high-explosive charge and/or via its incendiary (fire-causing) effects. ...
** PGU-15/B TP Target Practice
*Armor penetration of Armor-Piercing Incendiary ammunition, BHN-300 RHA, attack angle 30 degrees from vertical:[.]
** 76 mm at 300 meters
** 69 mm at 600 m
** 64 mm at 800 m
** 59 mm at 1,000 m
** 55 mm at 1,220 m
See also
* T249 Vigilante
*Gryazev-Shipunov GSh-6-30
The Gryazev-Shipunov GSh-6-30 (Russian: Грязев-Шипунов ГШ-6-30) is a Russian 30 mm rotary cannon aircraft-mounted and naval autocannon used by Soviet and later CIS military aircraft. The GSh-6-30 fires a 30×165mm, projectile ...
*Type 730 CIWS
The Type 730 is a Chinese seven-barrelled 30 mm Gatling gun/Rotary cannon CIWS. It has a PLA Navy designation H/PJ12. It is mounted in an enclosed automatic turret and directed by radar, and electro-optical tracking systems. The maximum ra ...
General:
*List of aircraft weapons
This is a list of weapons ( aircraft ordnance) carried by aircraft.
Guns
In World War I, aircraft were initially intended for aerial reconnaissance, however some pilots began to carry rifles in case they spotted enemy planes. Soon, planes were f ...
*List of multiple-barrel firearms
Below is a list of multiple-barrel firearms of all forms from around the world.Small Arms Illustrated, 2010
Pistols
Rifles
Flare launchers
Less lethal
Automatic rifles
Submachine guns
Shotguns
Machine guns
Grenade launchers
S ...
References
Bibliography
* Spick, Michael. ''The Great Book of Modern Warplanes'', Salamander Books, 2000. .
External links
General Electric GAU-8/A Avenger on USAF National Museum site
Hill Aerospace Museum, fas.org
Video of the GAU-8 Avenger test firing
{{DEFAULTSORT:GAU-8 Avenger
Aircraft guns
Rotary cannon
Multi-barrel machine guns
30 mm artillery
Military equipment introduced in the 1970s
Cold War weapons of the United States