During an instructional flight, the helicopter was at an altitude of 40 to 50 ft above ground level, at 60 knots, when the flight instructor intended to demonstrate a simulated engine failure and run-on landing. Although the flight instructor had intended to recover from the maneuver prior to an actual run-on landing, he noticed that he did not have enough rotor rpm to recover and elected to continue with the run-on landing. The helicopter then landed hard on a taxiway and slid about 300 ft before coming to rest upright. The flight instructor added that there were no preimpact mechanical malfunctions or failures with the helicopter that would have precluded normal operation. Examination of the helicopter by a Federal Aviation Administration inspector revealed damage to the aft engine bulkhead and wrinkles in the helicopter panels near the tail boom and rotor gear box.