After completion of a local solo flight, the student pilot was conducting the engine cooling shutdown procedure on the dry ramp when the helicopter suddenly became airborne, climbed about 30ft, and entered a nose down attitude impacting the ground. The helicopter came to rest upright, and the pilot was able to egress from the helicopter without further incident. The helicopter sustained substantial damage to the main rotor system, the tail boom, and the tail rotor system. The student pilot reported that he had engaged both the cyclic and collective friction prior to completing other post flight activities. Postaccident examination of the helicopter showed the collective friction to not be fully engaged. The friction was found at an approximate 90-degree angle to the collective lever, which corresponds to the friction not being fully engaged. The helicopter pilot’s flight manual states that the collective friction is to be on for the engine cooling shutdown procedure. No preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal flight operation were reported.