On April 23, 2011, at 1541 eastern daylight time, a D&D Aircraft Rotorway Exec, N614S, an experimental, amateur built helicopter, collided with the terrain during an off airport forced landing in Massillon, Ohio. The pilot received a minor injury while exiting the helicopter. The helicopter received substantial damage. The personal flight was being operated under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The local flight originated from a private field in Massillon, Ohio. The pilot reported that during cruise flight the engine speed increased to a high rpm and the power was no longer being transmitted through to the rotor system. He initiated an autorotation to a sloping, plowed field that was soft due to recent rain. The tail struck the ground during the landing flare and the main rotor blades contacted the tailboom. The helicopter rolled over due to the downward slope and the soft terrain. Postaccident inspection of the helicopter by the pilot/builder and Federal Aviation Administration inspectors revealed the inner race of the bearing on the secondary shaft, located above the transmission clutch, was worn into the shaft. The secondary shaft was designed by the pilot.