The Air Force version of the F-35 has fired its onboard Gatling gun at full capacity, the Pentagon’s Joint Program Office (JPO) said Thursday.
Earlier in August, an F-35A fired 181 rounds from its four-barrel, 25 millimeter wing-mounted gun during a ground test at Edwards AFB, Calif. The Air Force F-35A is the only one of the three Joint Strike Fighter variants that is equipped with an integral gun.
Both the short-takeoff, vertical landing F-35B for the Marine Corps and the Navy’s carrier-based F-35C will have the option of carrying the same gun in a belly-mounted pod.
The General Dynamics [GD] GAU-22/A cannon is internally-mounted in a “blister” on the Air Force F-35A’s left wing. The Marine Corps F-35B and Navy F-35C will have the option of carrying the gun externally in a belly-mounted pod. The gun is a more powerful version of the GAU-12 used on the AV-8B Harrier jump jet that the F-35B will replace. The 25mm round is larger than that carried by any of the Air Force’s legacy fighter aircraft, which fire 20mm rounds.
First shots were fired from an Air Force F-35 designated AF-2, a specially instrumented aircraft to gather data on stress loads and other metrics during the burst firing. The same specially instrumented aircraft was used in the most recent gun testing.
Engineers with the Joint Strike Fighter integrated test force are checking multiple systems connected to the gun’s operation, including the opening and closing of the door through which the rounds are fired, the spinning of its four barrels, air flow through vents that siphon off flammable gases and that the airframe itself can withstand the forces exerted by firing the powerful cannon.
Ground testing is scheduled to wrap up this month with airborne gun testing beginning in the fall, according to the JPO. The gun should be declared operational at the end of the system development and demonstration phase in 2017.
An F-35 flight sciences aircraft, AF-2, underwent instrumentation modifications and used a production version of the GAU-22/A gun. The ground tests were designed using software to replicate being in flight and the aircraft used a target practice round, PGU-23/U, which does not explode on impact.
The Marine Corps declared the jet ready for combat in late July, but its jets are operating with a version of the aircraft’s avionics software that does not allow for operation of the gun. F-35As in the fleet today are also operating with the 2B version of the software that does not include operation of the gun. The Air Force is scheduled to declare its first F-35 fleet operational in 2016 with incremental 3i software that also will not allow a pilot to use the gun. That capability will be included in the final 3F version of the software due to arrive in 2017.
Testing of the gun began on June 9, with shots fired from a stationary F-35A on the ground to “harmonize” the gun, meaning to make sure the aircraft withstood recoil and other forces, that the gun operated properly and that rounds hit a target accurately. The amount of rounds fired through the gun was incrementally increased until the firing of 181 rounds on Aug. 14.
Integrating the internal gun with the F-35 is a unique challenge because the aircraft must maintain its stealth capabilities. Therefore, the cannon fires through a door that lifts up, creating a hole in the outer skin of the aircraft when the pilot pulls the trigger, then lowers back into place preserving the aircraft low radar signature.
The GAU-22/A system will be further tested with a line production F-35A next year for integration with the jet’s full avionics and mission systems capabilities. Test pilots will then observe qualitative effects, such as muzzle flash, human factors, and flying qualities. The F-35 test team will also monitor the GAU-22/A’s performance and ensure all systems work as designed, validating that the aircraft can withstand the loads of a firing the gun, mitigating potential effects including vibrations, acoustics and airflow.