Pilot's Account
According to the pilot, the helicopter was in cruise flight at approximately 80 knots at 2,000 feet mean sea level (msl). Both doors had been removed, and the pilot was flying from the right seat. He reported that when he turned his head to the right, a blast of wind struck the back of his head, knocking off his glasses and headset. The pilot stated that he subsequently lost control of the helicopter, experiencing a sensation of flipping and spinning before he managed to recover control and continue the flight to his destination.
Damage
Examination of the helicopter revealed damage consistent with a mast bump event. Mast bumping is a condition where the rotor mast contacts the rotor blades, typically resulting from low rotor rpm or excessive maneuvering.
Manufacturer Guidance
According to the Robinson R-22 Pilot's Operating Handbook, in the section on doors-off operation, pilots are instructed to "keep head and arms inside cabin to avoid high velocity airstream."