Accident Overview
The pilot of an experimental helicopter reported that during cruise flight at approximately 700 feet above ground level, the top motor mount made of cast aluminum fractured. This failure caused a loss of belt tension to the main rotor system, preventing the pilot from maintaining adequate rotor rpm.
Autorotation and Landing
Facing diminishing rotor speed, the pilot executed an autorotation to a small backyard surrounded by trees. The helicopter made a hard landing, during which the main rotor blades flexed downward and struck the tailboom, severing it from the aircraft.
Aircraft Damage
The helicopter sustained substantial damage, including the separation of the tailboom from the fuselage due to rotor blade contact. The extent of damage to other components was not reported.
Pilot Report
The pilot, who was the sole occupant, provided the account of events, noting the unexpected failure of the cast-aluminum motor mount and the subsequent chain of events.