On September 6, 1993, at about 1300 eastern daylight time, a Ferrie Exec, Rotoway Kit, experimental helicopter, N71714, registered to Dean R. Ferrie, operating as a 14 CFR Part 91 personal flight, crashed while demonstrating an autorotation with power recovery. The helicopter sustained substantial damage. The private pilot and one passenger were not injured. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from a grass field adjacent to a private business in the vicinity of Delray Beach, Florida, about 19 minutes before the accident. The pilot stated to the NTSB investigator-in-charge that he had not flown the helicopter for about 3 months. He departed on a VFR flight at about 1200 hours and completed three takeoffs, three landings, and three autorotations before he returned to pick up a passenger for a local area flight. At about 1300, he was demonstrating an autorotation with power recovery to the passenger. He entered the maneuver at about 500 feet agl and assumed a 60 knot-attitude. A deceleration was initiated at about 35 to 40 feet agl. Initial collective pitch was applied at about 5 feet agl and the helicopter was leveled with cyclic. The pilot stated the rotor rpm was low so he lowered the collective pitch and the helicopter started spinning to the left. Right antitorque pedal was applied and the helicopter continued to spin to the left through 360 degrees. The pilot lowered the collective pitch and the helicopter collided with the terrain and rolled over on its left side. The pilot stated no attempt was made by the pilot to stop the rotation by increasing collective pitch prior to the helicopter colliding with the terrain.