On August 5, 2010, about 1000 eastern daylight time, an experimental, amateur-built Dayton JD-2, N43015, was substantially damaged during a forced landing, after a loss of power near Hollywood, Maryland. The commercial pilot was not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the personal flight conducted under the provisions of 14 Code of Federal Regulations Part 91. The local flight originated from the St. Mary's County Regional Airport (2W6), Leonardtown, Maryland. The pilot/builder reported that he was flying about 800 feet above the ground when he experienced a sudden increase in engine rpm, with a corresponding loss of thrust. He subsequently performed a forced landing to a highway; however, during the landing roll, the right wing struck a tree and sustained substantial damage. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the propeller assembly rotated without any corresponding engine crankshaft movement. The airplane was issued an experimental airworthiness certificate on March 20, 2005. It was equipped with a non-certificated Rotec R2800 series, 110-horsepower radial engine. According to maintenance records, the airplane was originally equipped with a Continental O-200-A series engine. On December 30, 2009, the pilot installed the Rotec engine and utilized the propeller assembly that was previously installed on the Continental engine. At the time of the accident, the engine had been operated for about 35 hours since it was installed, and approximately 10 hours since its most recent condition inspection, which was performed by the pilot on January 14, 2010. Additional examination of the engine by an FAA inspector revealed that the crankshaft tapered flange was scored, which corresponded with scoring observed inside the tapered propeller hub flange. The castellated nut and washer, which secured the propeller hub flange to the engine crankshaft, were found extremely scored and warped. In addition, the FAA inspector noted that the pilot did not possess the proper manufacturer technical data and tooling to remove and reinstall the propeller hub assembly on the accident engine.