Q  How are the barrels rotated  A  The rotational force is delivered by two hydraulic drive motors operating off of both main aircraft hydraulic systems AB  The motors deliver their torque to gearbox in the Hydraulic drive assembly  This in turn delivers the force to two drive shafts  The forward one goes to the rotor assembly on the GAU itself while the second delivers its power to the ammunition drum  Q  How long is typical spinup time  A  While the system is capable of operating at  rounds per minute it is limited to  while installed in the aircraft  Since the GAU has  barrels it needs to spin at th of the firing rate  Basically since its rotating a touch over  rpm the spinup time is almost instantaneous   On another point the statement on the gun gas on affecting the engines is complete rubbish  During the firing of the GAU the engines ingest so much gun gas that the engine igniters think super spark plugs must fire to ensure a stall does not occur  The engines also will ingest so much soot from the firings that they need to be water washed have water and a mild cleaning solution misted into the engines while running at approx  power periodically to remove soot from the blades  Anyone who has had to clean an A will tell you the gun gas goes just about everywhere aft of the nose