GAU-8 Avenger
Encyclopedia
The General Electric
GAU-8/A Avenger is a 30 mm
, hydraulically-driven seven-barrel Gatling-type
rotary cannon
that is mounted on the United States Air Force
's Fairchild Republic A-10 Thunderbolt II. It is among the largest, heaviest and most powerful aircraft cannons in the United States
military. Designed specifically for the anti-tank role, the Avenger delivers very powerful rounds at a high rate of fire.
and Philco-Ford offering competing designs. Both of the A-X prototypes, the YA-10 and the Northrop YA-9, were designed to incorporate the weapon, although it was not available during the initial competition, and the M61 Vulcan
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.
The gun is placed slightly off center in the nose of the plane with the front landing gear
positioned to the right of the center line, so that the actively firing cannon barrel is directly on the aircraft's center line. The Russian Gryazev-Shipunov GSh-6-30
is a similar class of weapon, although it is lighter with a higher fire rate, but has a lower muzzle velocity and overheats faster.
The A-10 and its GAU-8/A gun entered service in 1977. It was produced by General Electric
, 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
.
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.
's 20 mm round.
The standard ammunition mixture for anti-armor use is a four-to-one mix of PGU-14/B Armor Piercing
Incendiary, with a projectile weight of about 15.0 oz (425 grams or 6,560 grains) and PGU-13/B High Explosive Incendiary (HEI) rounds, with a projectile weight of about 12.7 oz (360 grams or 5,556.25 grains). The PGU-14/B's projectile incorporates a lightweight aluminum body, cast around a smaller caliber depleted uranium
penetrating core. The Avenger is lethal against tanks and all other armored vehicles.
A very important innovation in the design of the GAU-8/A shells 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 shells also have plastic driving band
s to improve barrel life. They are imposing to examine and handle, measuring 11.4 inches (289.6 mm) in length and weighing 1.53 pound (0.6939963261 kg) 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. Later this was changed to a fixed rate of 3,900 rpm. 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
and bolt
. Like the original Gatling gun
, the entire firing cycle is actuated by cam
s and powered by the rotation of the barrels. The barrels themselves are driven by the aircraft's dual hydraulic system.
The GAU-8/A ammunition 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 recycled back into the ammunition drum, instead of ejected from the aircraft, which would require considerable force to eliminate potential airframe damage. The feed system is based on that developed for later M61 installations, but uses more advanced design techniques and materials throughout, to save weight.
The muzzle velocity of the GAU-8/A is about the same as that of the M61 Vulcan
cannon, but its heavier ammunition is more destructive and has superior ballistic properties. Its time of flight to 4000 feet (1,219.2 m) is 30 percent less than that of an M61 round, the projectile decelerates much less rapidly after leaving the barrel, and it drops a negligible amount, about 10 feet (3 m) over the distance. 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 at 4000 feet (1,219.2 m) will hit the target within a 20 feet (6.1 m) radius circle. By comparison, the M61 is rated at 8 milliradians.
when fired. This configuration also provides space for the front landing gear, which are mounted slight off-center on the right 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
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 flame-outs of gas turbine
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 flame-out.
The recoil force of the GAU-8/A is 10,000 pounds-force
(45 kN), which is slightly more than the output of one of the A-10's two TF34 engines (9,065 lbf / 40.3 kN each). While this recoil force is significant, in practice cannon fire only slows the aircraft a few miles per hour.
developed for the AV-8B Harrier II aircraft, which is about the same size as the M61
but is considerably more lethal. 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
, and the Avenger forms the basis for the Dutch-developed Goalkeeper
naval air-defence gun. No current or contemplated aircraft other than the A-10, however, carries the full-up Avenger system.
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
GAU-8/A Avenger is a 30 mm
30 mm caliber
30 mm caliber ammunition is usually used in autocannon. Such ammunition includes NATO standard 30 × 173 mm and 30 × 113 mm and Soviet 30 × 165 mm ammunition widely used around the world....
, hydraulically-driven seven-barrel Gatling-type
Gatling gun
The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat...
rotary cannon
Rotary cannon
A rotary cannon, or Gatling-type cannon, is a rapid-firing weapon that utilizes multiple barrels in a rotating cluster to provide a sustained rate of fire greater than single-barrelled machine guns or automatic cannons of equivalent caliber...
that is mounted on the United States Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
's Fairchild Republic A-10 Thunderbolt II. It is among the largest, heaviest and most powerful aircraft cannons in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
military. Designed specifically for the anti-tank role, the Avenger delivers very powerful rounds at a high rate of fire.
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 ElectricGeneral Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
and Philco-Ford offering competing designs. Both of the A-X prototypes, the YA-10 and the Northrop YA-9, were designed to incorporate the weapon, although it was not available during the initial competition, and the M61 Vulcan
M61 Vulcan
The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...
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.
The gun is placed slightly off center in the nose of the plane with the front landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...
positioned to the right of the center line, so that the actively firing cannon barrel is directly on the aircraft's center line. The Russian Gryazev-Shipunov GSh-6-30
Gryazev-Shipunov GSh-6-30
The Gryazev-Shipunov GSh-6-30 is a Russian 30 mm cannon used by Soviet and later CIS military aircraft.The GSh-6-30, designed in the early 1970s and entering service in 1975, is a six-barreled Gatling gun similar in design to the Gryazev-Shipunov GSh-6-23. It was based on the naval AO-18 used in...
is a similar class of weapon, although it is lighter with a higher fire rate, but has a lower muzzle velocity and overheats faster.
The A-10 and its GAU-8/A gun entered service in 1977. It was produced by General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
, though General Dynamics Armament and Technical Products has been responsible for production and support since 1997 when the division was sold by Lockheed Martin
Lockheed Martin
Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....
to General Dynamics
General Dynamics
General Dynamics Corporation is a U.S. defense conglomerate formed by mergers and divestitures, and as of 2008 it is the fifth largest defense contractor in the world. Its headquarters are in West Falls Church , unincorporated Fairfax County, Virginia, in the Falls Church area.The company has...
.
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.
Design
The GAU-8 itself weighs 620 pounds (281.2 kg), but the complete weapon, with feed system and drum, weighs 4029 pounds (1,827.5 kg) with a maximum ammunition load. It measures 19 foot from the muzzle to the rearmost point of the ammunition system, and the ammunition drum alone is 34.5 inches (87.6 cm) in diameter and 71.5 inches (1.8 m) long. The magazine can hold 1,174 rounds, although 1,150 is the typical load-out. Muzzle velocity when firing Armor-Piercing Incendiary rounds is 3250 feet per second (990.6 m/s), almost the same as the substantially lighter M61 VulcanM61 Vulcan
The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...
's 20 mm round.
Armor-piercing shot and shell
An armor-piercing shell is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions...
Incendiary, with a projectile weight of about 15.0 oz (425 grams or 6,560 grains) and PGU-13/B High Explosive Incendiary (HEI) rounds, with a projectile weight of about 12.7 oz (360 grams or 5,556.25 grains). The PGU-14/B's projectile incorporates a lightweight aluminum body, cast around a smaller caliber depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...
penetrating core. The Avenger is lethal against tanks and all other armored vehicles.
A very important innovation in the design of the GAU-8/A shells 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 shells also have plastic driving band
Driving band
The driving band or rotating band is part of an artillery shell, a band of soft metal near the middle of the shell, typically made of gilding metal, copper or lead...
s to improve barrel life. They are imposing to examine and handle, measuring 11.4 inches (289.6 mm) in length and weighing 1.53 pound (0.6939963261 kg) 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. Later this was changed to a fixed rate of 3,900 rpm. 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-loading weapon
A breech-loading weapon is a firearm in which the cartridge or shell is inserted or loaded into a chamber integral to the rear portion of a barrel....
and bolt
Bolt (firearm)
A bolt is a mechanical part of a firearm that blocks the rear of the chamber while the propellant burns.In manually-operated firearms, such as bolt-action, lever-action, and pump-action rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas...
. Like the original Gatling gun
Gatling gun
The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat...
, the entire firing cycle is actuated by cam
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...
s and powered by the rotation of the barrels. The barrels themselves are driven by the aircraft's dual hydraulic system.
The GAU-8/A ammunition 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 recycled back into the ammunition drum, instead of ejected from the aircraft, which would require considerable force to eliminate potential airframe damage. 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 from 2100 to 4200 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 carried by comparable Close Air Support aircraft.The muzzle velocity of the GAU-8/A is about the same as that of the M61 Vulcan
M61 Vulcan
The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...
cannon, but its heavier ammunition is more destructive and has superior ballistic properties. Its time of flight to 4000 feet (1,219.2 m) is 30 percent less than that of an M61 round, the projectile decelerates much less rapidly after leaving the barrel, and it drops a negligible amount, about 10 feet (3 m) over the distance. The GAU-8/A accuracy when installed in the A-10 is rated at "5 mil
Angular mil
An angular mil, also mil, is a unit of angle. All versions of the angular mil are approximately the same size as a trigonometric milliradian.-History:The milliradian was first identified in the mid nineteenth Century...
, 80 percent", meaning that 80 percent of rounds fired at 4000 feet (1,219.2 m) will hit the target within a 20 feet (6.1 m) radius circle. By comparison, the M61 is rated at 8 milliradians.
Recoil
Each barrel fires when it reaches roughly the 9 o'clock position, when viewed from the front of the plane. Because the gun's recoil forces could push the entire plane off target during firing, the weapon itself is mounted off-center in the other direction, toward the 3 o'clock position, so that the firing barrel lies directly on the aircraft's center line. 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 pitch and/or yawYaw
The word yaw can refer to:* Yaw angle, one of the Tait-Bryan angles, describing the heading of a vehicle or machine, and some other related elements:**Yaw system, component responsible for the orientation of a wind turbine towards the wind....
when fired. This configuration also provides space for the front landing gear, which are mounted slight off-center on the right 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
Flameout
A flameout refers to the failure of a jet engine caused by the extinction of the flame in the combustion chamber. It can be caused by a number of factors, including fuel exhaustion; compressor stall; insufficient oxygen supply; foreign object damage ; severe inclement weather; and mechanical...
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 flame-outs of gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
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 flame-out.
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...
(45 kN), which is slightly more than the output of one of the A-10's two TF34 engines (9,065 lbf / 40.3 kN each). While this recoil force is significant, in practice cannon fire only slows the aircraft a few miles per hour.
Variants
Some of the GAU-8/A technology has been transferred into the smaller 25 mm GAU-12/U EqualizerGAU-12 Equalizer
The General Dynamics GAU-12/U Equalizer is a five-barrel 25 mm Gatling gun-style rotary cannon. The GAU-12/U is used by the United States, Italy and Spain, which mount the weapon in their fighter jets such as the AV-8B Harrier II, airborne gunships such as the Lockheed AC-130, and land-based...
developed for the AV-8B Harrier II aircraft, which is about the same size as the M61
M61 Vulcan
The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...
but is considerably more lethal. GE has also developed the GAU-13/A
GAU-13 cannon
The General Electric GAU-13/A is a 30 mm electric Gatling Gun derived from the GAU-8 Avenger cannon.-Description:The GAU-13 was developed in the late 1970s for use in gun pod applications for fighter aircraft and attack aircraft use, primarily for air-to-ground and anti-tank attacks.The GAU-13/A is...
, a four-barreled weapon using GAU-8/A components, which has been tested in podded form as the GPU-5/A
U.S. aircraft gun pods
The idea of the gun pod as a concept largely came into its prime during and period following World War II. So-called "package gun" installations on US medium and light bombers, such as the B-25 Mitchell and A-26 Invader, were probably the first such attempts by the United States military...
, and the Avenger forms the basis for the Dutch-developed Goalkeeper
Goalkeeper CIWS
Goalkeeper is a Dutch close-in weapon system introduced in 1979 and in use , which primarily defends ships against incoming missiles and ballistic shells. This system consists of an autocannon and an advanced radar which in typically six seconds detects incoming fire, determines its trajectory,...
naval air-defence gun. No current or contemplated aircraft other than the A-10, however, carries the full-up Avenger system.
Specifications
- Accuracy: 80% of rounds fired at 4000 feet (1,219.2 m) range hit within a 20 feet (6.1 m) radius
- PGU-14/B API Armor PiercingArmor-piercing shot and shellAn armor-piercing shell is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions...
Incendiary (DUDepleted uraniumDepleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...
) - PGU-13/B HEI High explosive incendiaryHigh explosive incendiaryIn warfare, High-explosive incendiary is a type of ammunition specially designed to pierce armor, fragment, and ignite readily combustible materials....
- PGU-15/B TP Target Practice
- PGU-14/B API Armor Piercing
- Armor penetration:
- 69 mm at 500 meters
- 38 mm at 1000 meters
See also
- List of aircraft weapons
- List of multiple barrel firearms
- Goalkeeper CIWSGoalkeeper CIWSGoalkeeper is a Dutch close-in weapon system introduced in 1979 and in use , which primarily defends ships against incoming missiles and ballistic shells. This system consists of an autocannon and an advanced radar which in typically six seconds detects incoming fire, determines its trajectory,...
- Gryazev-Shipunov GSh-6-30Gryazev-Shipunov GSh-6-30The Gryazev-Shipunov GSh-6-30 is a Russian 30 mm cannon used by Soviet and later CIS military aircraft.The GSh-6-30, designed in the early 1970s and entering service in 1975, is a six-barreled Gatling gun similar in design to the Gryazev-Shipunov GSh-6-23. It was based on the naval AO-18 used in...
External links
- General Electric GAU-8/A Avenger on USAF National Museum site
- www.fas.org: GAU-8 Avenger, Hill Aerospace Museum (retrieved 27 April 2005)
- Video of the GAU-8 Avenger test firing