The night training flight was conducted using night vision goggles, and a crew change was conducted while helicopter continued to operate. The maneuvers conducted included hovering, straight-in and 180° autorotations to touchdown, hydraulics off flight, and stuck-pedal flight to touchdown. The flight instructor and the two pilots described the maneuvers as smooth and controlled with no hard landings. A post-flight inspection revealed substantial damage to the left vertical stabilizer, and “rub marks and scratches” on the underside of each main rotor blade consistent with main rotor contact. A main rotor strike of the vertical fin likely occurred during a hard landing at the termination of an autoration, but the investigation was unable to determine the specific training event during which the main rotor strike occurred.