On August 7, 2011, at 1332 central daylight time, an experimental amateur-built RV-7A, N462WP, was substantially damaged during a forced landing after takeoff from Western Kentucky Airpark (5KY3), Paducah, Kentucky. The certificated private pilot/owner/builder was not injured and the passenger incurred minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight, which was conducted under the provisions of 14 Code of Federal Regulations Part 91. After an uneventful preflight inspection and engine start, the pilot taxied the airplane and conducted a pre-takeoff run-up of the engine. During the run-up the pilot tested the dual ignition system and the primary and secondary engine control computers for proper function. Noting no abnormalities, the pilot proceeded with the takeoff. While climbing the airplane at an airspeed of about 100 knots, and about 200 to 300 feet above the ground, the pilot noted that the engine began to "stumble" and lost partial power. The pilot responded by switching engine control computers, richening the mixture, and then began searching for a forced landing site. He did not note any abnormal engine instrument indications, and could not recall the engine's rpm during the descent. During the forced landing to a nearby road, the airplane struck a mailbox and a ditch, damaging the left wing tip and the right wing spar. An experimental amateur-built special airworthiness certificate was issued for the airplane on February 27, 2010. The airplane was powered by an automotive-type, Mazda 13B engine, rated at 200 horse power. The fuel-injected, computer-controlled rotary engine was mated to a gear reduction drive unit and a two-blade constant speed propeller. At the time of the accident the airplane had accumulated 70 total hours of operation, while the engine had accumulated 80 total hours of operation. After the airplane was recovered to the pilot's hangar, the pilot and a Federal Aviation Administration inspector conducted a test run of the airplane's engine on the day following the accident flight. According to the inspector, the engine started immediately and exhibited smooth and continuous operation at an idle power setting. In the 8 months following the accident, the pilot rebuilt the airplane and continued attempts to troubleshoot the loss of power. Despite numerous attempted on-ground test runs at various power settings, including high power settings, the pilot was unable to duplicate or otherwise definitively determine a reason for the loss of power during the accident flight. The pilot held a private pilot certificate with a rating for airplane single engine land. He reported 166 total hours of flight experience, 72 hours of which were in the accident airplane make and model. The 1453 recorded weather at Barkley Regional Airport (PAH),Paducah, Kentucky, located about 11 nautical miles northwest of the accident site, included winds from 220 degrees magnetic at 8 knots, clear skies, 10 statute miles visibility, temperature 32 degrees C, dewpoint 24 degrees C, and an altimeter setting of 29.82 inches of mercury.