The pilot stated that while landing downwind, the helicopter began to yaw to the right. The pilot applied left pedal and forward cyclic inputs in an attempt to correct the yaw, however, the helicopter continued to rotate and descend. Shortly thereafter, the helicopter touched down on both skids and rolled onto its right side, which resulted in substantial damage to the airframe and rotor blades. The pilot reported no mechanical anomalies that would have precluded normal operation.