GAU-8 Avenger

Name	GAU-8 Avenger
Caption	The GAU-8/A Avenger's barrel and breech assembly (ammunition drum off edge of photo).
Origin
Type	Gatling-style autocannon
Is ranged	yes
Service	1977–present
Used by	United States
Manufacturer	General Electric
Number	Approx. 715
Variants	GAU-12/U Equalizer GAU-13/A
Weight
Length	(total system)
Part length
Dispersion	5 Milliradians, 80 percent circle
Width	(barrel only)
Cartridge	30 × 173 mm
Caliber	30 mm caliber
Barrels	7
Action	Electric-Motor, Hydraulic-Driven
Rate	4,200 rpm (rounds per minute)
Velocity
Max range	Over
Feed	Linkless feed system

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.

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 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 more quickly.

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.

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. The magazine can hold 1,174 rounds, although 1,150 is the typical load-out. Muzzle velocity when firing Armor-Piercing Incendiary rounds is , almost the same as the substantially lighter M61 Vulcan'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. 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. 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.

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 yaw 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.

The recoil force of the GAU-8/A is 10,000 pounds-force (45 kN), 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 Equalizer 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.

Specifications

Accuracy: 80% of rounds fired at range hit within a radius

*PGU-14/B API Armor Piercing Incendiary (DU)

* PGU-13/B HEI High explosive incendiary

* PGU-15/B TP Target Practice

Armor penetration:

* 69 mm at 500 meters

* 38 mm at 1000 meters

See also

List of aircraft weapons

Goalkeeper CIWS

Gryazev-Shipunov GSh-6-30

References

Spick, Michael. The Great Book of Modern Warplanes, Salamander Books, 2000. ISBN 1-84065-156-3.

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

Category:Aircraft guns Category:Rotary cannons Category:Multi-barrel machine guns Category:30 mm artillery