The purpose of the flight was for the helicopter-rated instructor pilot receiving instruction to become more familiar with the accident make and model helicopter. The intention of the flight instructor giving instruction was to demonstrate an autorotation on takeoff at low altitude, with the student following along on the controls. After ascending to an altitude of about 150 feet and an airspeed of about 50 knots, the instructor explained to the student that he was going to lower collective, but would not add cyclic to maintain airspeed. The instructor stated, “I lowered collective and could feel him [the student] on the collective, so I knew he was there. I then put right pedal in, split the needles, and then felt him [the student] pull back on the cyclic and pull up on the collective. I said ‘…no, push down,’ and I forced the cyclic forward.” The flight instructor said that the rotor RPM had by then decayed outside of normal parameters and that the student kept pulling up on the collective. “I tried to roll on power and force the cyclic forward, but we were descending too fast.” The student stated that during the demonstration he looked down at the rotor RPM and noticed that it was about 320 RPM, and that it stayed that low as the helicopter approached the ground. The student stated that he repeatedly told him [the flight instructor giving instruction] “low RPM" at least 5 times. The student added that after the hard landing the instructor told him that he [the student] had grabbed the controls because the helicopter didn’t pitch forward like he had intended it to do. The student stated, “I told him I hadn’t touched any of the controls and the reason he had no control was probably because the rotor RPM was so low.” An examination of the airframe by a Federal Aviation Administration inspector did not reveal any pre-impact anomalies. Additionally, neither pilot reported a malfunction of the airframe or engine.