On October 18, 2011, at 1623 eastern daylight time, an experimental amateur-built, Graff Bearhawk, N5456C, experienced a partial loss of engine power and made a forced landing near Woodrow, West Virginia. The airplane sustained substantial damage to the airframe and wings. The personal flight was operating under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The private pilot and passenger were not injured. The flight originated from a private strip in Upperglade, West Virginia, at 1745. The pilot stated that he was flying for approximately 20 minutes in a slow flight configuration. He began to circle around a point for approximately 8 minutes when the engine started to lose power. The carburetor heat was turned on with no increase in power. The engine continued to lose power until altitude could not be maintained. The pilot made a force landing on a highway. During the landing roll out the right wing collided with a sign and the airplane veered off into a ditch. The pilot said that he knew the conditions were favorable for carburetor icing at the time of the flight but he applied the carburetor heat. He did not report any flight control anomalies prior to the flight. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the airplane's right wing spar was damaged and the fuselage was buckled. The airplane was recovered, and no anomalies were noted during the engine cursory examination. An engine run was conducted but was limited to 1,800 rpm due to propeller damage. No anomalies were noted during the engine run that would have precluded normal operation. The nearest weather station was North Central West Virginia (CKB), Clarksburg, West Virginia located approximately 40 nautical miles west of the accident site reported; the ambient temperature at the time of the accident was 72°F and the dew point was 70°F. According to the FAA icing probability chart, this temperature/dew point combination meets the conditions favoring serious icing formation at glide power.