476th vfighter Group Weapon Fact Sheet 1: GAU-8/A Avenger

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1 Weapon Fact Sheet 1: GAU-8/A Avenger INTRODUCTION The gun subsystem consists of a seven-barrel GAU-8/A 30mm Gatling gun and a doubleended link less feed system with a capacity up to 1,174 rounds of percussion primed ammunition. The gun system retains all spent cases or dud rounds. The gun system is electrically controlled and hydraulically driven. The gun-drive motors normally provide a single firing rate and are pressurized from the two independent hydraulic systems. If one aircraft hydraulic system fails or one hydraulic drive motor is inoperable, the gun will operate at a reduced rate. It fires large armour-piercing shells at a rate of 3,900 rounds per minute. The GAU-8/A is the primary weapon of the A-10. With over 1,150 rounds of 30mm high explosive incendiary (HEI) and armor piercing incendiary (API) rounds, combined with a sustained rate of fire of 62 rounds per second, the A-10 pilot is provided unsurpassed staying power and flexibility. The GAU-8/A characteristics of increased standoff, high accuracy, and sustained firepower make strafe the most reliable and effective method for the A-10 to deliver firepower against a ground target. DESIGN The GAU-8/A itself weighs 620 pounds (280 kg), but the complete weapon, with feed system and drum, weighs 4,029 pounds (1,828 kg) with a maximum ammunition load. It measures 19 ft in (5.931 m) from the muzzle to the aft point of the ammunition system, and the ammunition drum alone is 34.5 inches (88 cm) in diameter and 71.5 inches (1.82 m) long. Power for operating the gun is provided by twin 77 hp. electric motors. The magazine can hold 1,174 rounds, although 1,150 is the typical load due to the 575 round capacity of the loading cart. Muzzle velocity when firing Armor-Piercing Incendiary rounds is 3,250 feet per second (990 m/s), almost the same as the substantially lighter M61 Vulcan's 20 mm round. 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 bands to improve barrel life. They are imposing to examine and handle, measuring 11.4 inches (290 mm) in length and weighing 1.53 pounds (0.69 kg) or more. The GAU-8/A was built with the specifications that 80 percent of the bullets must fall within a 5-mil diameter of the desired aim point and 100 percent must fall within 13 mils. Dispersion, however, does increase as the gun heats up. After six to eight passes of 150 rounds each with only 1.5 minutes between bursts, gun dispersion can increase to 30 mils for 100 percent and 18 to 20 mils for 80 percent of rounds fired. Dive angle does not affect dispersion, only the bullet footprint.

2 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. 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 cams and powered by the rotation of the barrels. The GAU-8/A ammunition is link-less, 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 Each barrel fires when it reaches roughly the 9 o'clock position, as viewed from the front of the aircraft. 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, so that the firing barrel lies directly on the aircraft's centerline. The firing barrel also lies just below the aircraft's center of gravity; being bore sighted 2 degrees below the aircraft's waterline. This arrangement centers the recoil forces, helping to prevent changes in pitch and/or yaw when fired. This configuration also provides space for the front landing gear, which is mounted slightly off-center on the right side of the nose. The recoil force of the GAU-8/A is 10,000 pounds feet (45 kn), which is slightly more than the output of one of the A-10's two TF34 engines. While this recoil force is significant, and despite myths to the contrary, gun firing does not slow the aircraft. The GAU-8/A goes through a barrel clearing cycle within 0.5 seconds after every firing. The goal when designing the gun was to have no unfired or wasted rounds in the barrel. Additionally, the gun can detect a broken firing pin (resulting in a live round). The cockpit gun unsafe light will illuminate if the clearing cycle is not completed in 2.5 seconds. If two broken firing pins are detected, a gun unsafe indication will result. If the clearing cycle is interrupted by safing the gun, a gun unsafe indication will result. The cooling cycle was designed to eliminate increased bullet dispersion due to barrel heating and rotates the barrels under a schedule following trigger release. To cool the barrel, the GAU-8/A will automatically cycle at 24, 60, 100, and 150 seconds after firing. The cycle can be interrupted at any point by squeezing the trigger. Barrel cooling also stops when the master arm or rotate switch is set to the safe position.

3 COMBAT CONSIDERATIONS The GAU-8/A is highly effective against all types of ground vehicle and infantry, and can also be effective against certain types of building/fortification. It is often the first choice weapon for the A-10C pilot and any FAC(A) or JTAC calling in fire. While other weapons may have a higher probability of kill, they almost always come with a larger risk estimate distance and therefore a high probability of causing collateral damage. In addition to its lethality, the A-10C s ability to deliver GAU-8/A round on target with a high degree of accuracy combines to make it a highly lethal weapon. Despite its effectiveness however, pilots must consider the fact that employing the gun will almost always bring them into range of SHORAD and other ground fire threats that can be avoided with the use of other weapons. A good assessment of risk vs. results must be made before any attack. Although it must also be said that, at low level, the GAU-8/A is one of the longest reaching weapon systems available to the A-10C. The only weapons exceeding the reach of the GAU-8/A at low level are the AGM-65 Maverick and the Hydra 70 FFAR series. Armour penetration (PGU-14 API): 69 mm at 500 meters (1,600 feet/0.25 NM) 38 mm at 1,000 meters (3,300 feet/0.5 NM) AMMUNITION TYPES PGU-15 TP Ball practice round used for training PGU-14 API Armor Piercing Incendiary round. Loaded along with HEI in a 4:1 ratio as combat mix PGU-13 HEI - High Explosive Incendiary round. Can be loaded alone where anti-armor capability is not necessary to increase gun effectiveness against soft skinned targets.

4 A-10C AVIONICS INTEGRATION A/G Gun Attack Modes Air-to-surface gun attacks can be accomplished in GUNS and CCIP master modes. GUNS mode offers CCIP reticle, CCIP guns cross, 4/8/12 reticle, and wind corrected 4,000 foot gun cross. If a fixed sight (wind corrected fixed gun cross or 4/8/12 reticle) is selected in guns, then in CCIP the 4K wind corrected gun cross will be displayed (when the gun is armed). In HARS with the gun armed, a fixed, non-wind corrected 4K gun cross is displayed. Strafe Symbology CCIP Gun Reticle The default sight for the gun is the CCIP gun reticle. The CCIP reticule is corrected for all forces influencing the bullets after the gun has reached full speed (approximately 0.5 second). Some of these factors include deceleration, gravity drop, aircraft angle of attack, gun barrel rotation, and winds. The gun reticle consists of a 1 mil sized pipper at the center of a 50-mil circular reticle with range marks at 12, 3, 6, and 9 o clock. An analog range bar with a 5-mil tab indicates the slant range to the computed point of impact in thousands of feet. The analog range bar is located just inside the reticle and moves counter clockwise from the 12 o clock position as slant range to the target decreases. A hash mark at the end of the analog range bar indicates current slant range in thousands of feet as read from the reticle clock position. For example, with the hash mark at the 6 o clock position, current slant range is 6,000 feet. Slant ranges can be displayed from 0 to 12,000 feet. Outside of 12,000 feet, the range bar remains fixed at the 12 o clock position but the range numeric remains as long as a valid solution exists. The 2-digit range numeric shows the range in nautical miles beginning at 0.1 and increasing in 0.1 increments to 9.9. A IFFCC option configurable by the pilot is to display the range numeric in kilometers. In this case, a K will follow the range numeric, and the maximum range that will be displayed is 99K. The CCIP gun reticle includes two moving target indicators (MTI).The two vertical, 5-mil lines to the left and right of the pipper can be used to estimate the lead required for a moving target. These lines expand or contract as the slant range and bullet time of flight is changed. The MTI assumes the target is moving perpendicular to the aircraft at a rate of 20 knots. By placing the target under the MTI with the gun pipper in front of the direction of motion, the target and bullets should arrive at the same point at the same time. Use the MTI to estimate movement and deliver a burst of sufficient length and dispersion to increase the probability of a hit.

5 When combat mix ammunition (CM) is loaded, the CCIP gun reticule will contain two pippers. The pipper in the center of the CCIP gun reticule indicate the impact point for API rounds, the impact point for the HEI rounds is indicated by the second pipper which will change position relative to the center of the reticule. HEI rounds are lighter, and have a higher muzzle velocity initially, but due to higher drag they decelerate quicker than API. Consequently at long ranges HEI will land short of API rounds. Since the CM setting for bullet type optimizes the CCIP sight for API, notice that HEI rounds impact short at long ranges. The API will be on target and slightly later than the HEI impacts. This divergence becomes prevalent at slant ranges greater than 12,000 feet in dives of 30 degrees or less; greater than 15,000 feet S/R for 45 degrees of dive and almost negligible in 60-degree HAS. CCIP Gun Cross The IFFCC CCIP gun cross displays the same computed impact point as the CCIP gun reticle, using more compact symbology. The gun cross consists of a 2-mil pipper and a 4-mil gap, and each line segment of the cross is 5 mils long making the cross a total of 20 mils across. The horizontal line at the top of the cross helps to distinguish it from a non-computed gun sight. Gun Minimum Range Symbology A minimum range caret (MRC) is available in Guns and CCIP master modes for the CCIP gun reticle and CCIP gun cross. This gun MRC defines a minimum recovery altitude that is calculated using the minimum altitude entered in the IFFCC 30 MM submenu. The MRC also provides a time-to-go indication before aircraft recovery from guns pass must begin (four Gs in 2 seconds WINGS LEVEL is the assumed recovery). The caret is clamped vertically next to the top of the 12 o clock tick when there are 5 seconds or more until recovery must begin. The caret begins descending vertically when the time-to-go to the minimum recovery altitude (at current rate and angle of descent) decreases below 5 seconds. When the aircraft is less than 5 seconds above the minimum recovery altitude (at current rate and angle of descent), the caret will be displayed below the top of the 12 o clock tick and above the 3 o clock tick. When the aircraft is at the minimum recovery altitude, the caret will be next to the 3 o clock tick. When the aircraft is less than 5 seconds past (or below) the minimum recovery altitude (at current rate and angle of descent), the caret will be displayed below the 3 o clock tick and above the bottom of the 6 o clock tick. The caret will be clamped at the 6 o clock tick when the aircraft is 5 seconds or more below the minimum recovery altitude. Setting the minimum altitude in the 30 MM submenu to 0 feet deselects the gun CCIP minimum range cue display.

6 Bullets at Target Altitude IFFCC also incorporates a valuable training tool for feedback on dry strafe passes. The bullets at target altitude (BATA) is a small flashing circle that appears in the HUD at the point on the ground where the IFFCC computer predicts the bullets will impact. This estimation is based on aircraft altitude above the target and bullet TOF for the calculated slant range. The BATA appears, after the gun trigger is depressed, at the end of the first bullet s TOF expiration when Master Arm is not safe. 4/8/12 Gun Reticle Toggling the SEL rocker on the UFC or cycling DMS L/R with HUD-SOI will display the 4/8/12 gun reticle. IFFCC corrects for crosswinds and the pilot elevates the sights for slant range. The 4/8/12 gun reticle displays three wind-corrected fixed- range pippers representing 4000, 8000, and feet slant range solutions; the analog range bar is not present. The 4/8/12 reticule can be useful when accurate target elevation data is not available.

7 Wind Corrected Gun Cross The wind-corrected gun sight (WCGS) is similar in appearance to the CCIP gun cross, except it has no horizontal bar at the top and no range numeric. The WCGS is a cross fixed at 41 mils depression from the ZSL. Elevation of the gun sight for targets inside or beyond 4,000 feet slant range must be estimated by the pilot, and corrections made by moving the aircraft. Like the 4/8/12 gun reticle, this sight is useful when target elevation is unavailable.