N1CR

The instructor pilot provided instruction to the private pilot and conducted practice autorotation landings. The instructor pilot demonstrated an autorotation and during the landing the helicopter slid on the skids for about 10-15 feet before the skids dug into the soft landing surface. The helicopter began to pitch nose down so both pilots applied aft cyclic and up collective. The helicopter continued to pitch nose down when the main rotor impacted the ground, which resulted in the helicopter rolling on its right side. The helicopter sustained substantial damage to the main rotor blades, fuselage, and tail boom. The instructor pilot reported no preaccident mechanical malfunctions or anomalies that would have precluded normal operation.