On March 24, 1995, at 1030 eastern standard time, a Roggio Rotorway Executive helicopter, N34WR, collided with trees short of runway 20, while executing an autorotation at Toccoa Field in Toccoa, Georgia. The training flight operated under the provisions of 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The homebuilt helicopter was substantially damaged, and the commercial rated pilot was not injured. The flight departed Toccoa, Georgia, at 1025 hours. The pilot had completed a normal takeoff and landing to runway 02, and was on the second approach when the pilot heard two loud "pops." After observing a drop in engine and rotor RPM, the engine quit, and the pilot entered an autorotation. Since no other cleared area was nearby, the pilot selected a wooded area for the emergency landing. As the helicopter approached the trees, the pilot maneuvered the helicopter to lessen the impact forces with the trees. An examination of the airframe and engine assembly failed to disclose a mechanical problem or system malfunction. Flight and engine power control continuity were established during the post accident examination. There were no engine problems observed during the wreckage examination which would have prevented the normal operation of the engine. A review of applicable weather data indicated that conditions were favorable for the formation of carburetor icing. The pilot did not report the use of carburetor heat during the approach.