On July 11, 1996, at 1730 central daylight time, a Hiller UH-12E, N102HT collided with the ground and was substantially damaged during a forced landing near Cottondale, Florida. Neither of the two commercial pilots were injured. The helicopter was being operated under the provisions of Title 14 CFR Part 91 by the pilot. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed for the local flight. The flight departed Jackson Heliport at 1715 Central Daylight Time. Approximately two minutes into the climbout, the pilots felt a vibration in the airframe followed by a loud bang. The pilots initially stated that the helicopter had lost tail rotor control, at which time they selected a field for a forced landing. As the pilots attempted to control the helicopter, they reported that the flight controls would not respond to the inputs. Total control of the helicopter was lost; the helicopter impacted the ground inverted. Examination of the helicopter disclosed that the main drive clutch and engine gimble ring with the torsional coupling had failed. Debris from the failed components was not recovered for examination. A review of the maintenance logs showed that the drive coupling assembly had 511 hours of total time in service since new. The wreckage examination also disclosed that the entire transmission assembly had rotated from its normally installed position, and that the flight control rods were displaced from their normal positions.