On May 20, 1998, at 0925 central daylight time, a Harding Revolution Mini-500B experimental homebuilt helicopter, N6144S, owned and operated by the pilot, was destroyed during a forced landing following the loss of the main rotor drive near Grove, Oklahoma. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 CFR Part 91 personal flight. The private pilot, sole occupant of the aircraft, sustained minor injuries. The flight originated from the Grove Municipal Airport, about 25 minutes before the accident. The pilot reported that he had adjusted the alignment of the main drive belt and engine. During the ensuing personal/test flight of the helicopter, while at a cruising altitude of 1,350 feet MSL, he felt a "sudden hesitation and [smelled the] odor of smoke." While he was "determining if [a] serious malfunction existed," the helicopter experienced a loss of main rotor drive and altitude, "along with a stronger burning odor." The pilot initiated an autorotation to a field adjacent to a school. However, prior to reaching the intended landing area, the helicopter struck a parked pickup truck, "flipped over, landed in [the] field and started on fire." The helicopter was destroyed by the postimpact fire. The pilot had accumulated a total of 59 flight hours in helicopters, of which 14 hours were accumulated in his homebuilt helicopter.