On June 30, 2003, at 1802 mountain standard time, a Robinson R22 Beta, N7508E, made a hard landing during a practice autorotation near Chandler, Arizona. Quantum Helicopters, Inc., was operating the helicopter under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) and student were not injured; the helicopter sustained substantial damage. The flight departed Chandler Municipal Airport (CHD), Chandler, about 1715, for the local instructional flight. Visual meteorological conditions prevailed and no flight plan had been filed. The CFI reported that he initiated an announced "throttle chop" about 600 feet above ground level (agl) to the student who was training for his flight instructor certificate. Five seconds after lowering the collective, the student turned into the wind. While in the turn the student applied aft cyclic. The CFI brought this to the student's attention; the student applied forward cyclic. The rotor rpm began to decay. The CFI stated "I've got it," and attempted to slow the helicopter from about 75 knots indicated airspeed (KIAS) and recover the rpm. He felt the student on the controls. The CFI stated again, "I've got it" and noticed that the rpm was "dangerously low" at an altitude about 60 feet agl. The CFI attempted a low rotor rpm recovery maneuver but was unable to recover the lost rpm. About 30 feet agl prior to impact, the CFI noted the student's hands in the air, relinquishing the controls. As the helicopter descended, the CFI attempted to keep it level and applied aft cyclic. About 3 seconds prior to impact, he felt a shudder from the helicopter. The helicopter hit on the forward portion of the skids and the main rotor struck the tail boom. The right skid dug into the ground and the helicopter rolled over and came to rest on its right side. The student reported the CFI initiated the second "throttle chop" of the flight. The student lowered the collective and entered an autorotation. During a turn into the wind, the airspeed became excessively low so he "nosed over." Then he was told to watch his rpm. He rolled out of the turn and the low rotor rpm horn sounded. The CFI said, "I have control." The student reported that after the CFI stated that three times, he relinquished control. No mechanical malfunctions were noted with the helicopter.