On December 4, 2013, about 1240 eastern standard time, an experimental, amateur-built Thompson Sparrow II, N5955Y, was substantially damaged when it impacted terrain near Jeromesville, Ohio. The pilot sustained serious injuries. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight originated from a private airstrip about 1230.The pilot informed Federal Aviation Administration (FAA) inspectors that he was in the process of testing a new carburetor that he recently installed. After conducting some taxi testing with the newly installed carburetor, he flew the airplane around his farm without incident. He did not recall the events after that point in time. The pilot believed that he took off again and that the engine lost power, but he was unsure at what point during the flight that might have occurred. He recalled that he might have been attempting to return to the runway at the time of the accident. The airplane came to rest upright. The propeller assembly and engine cowling had separated and were located in the debris path. The propeller blades remained attached to the hub and appeared undeformed. The nose landing gear had collapsed. The nose and center fuselage structure was deformed. Both wings were twisted and exhibited leading edge crush damage. The flight controls remained attached to the wing. The empennage appeared intact with the exception of the lower portion of the rudder, which was deformed. The fuel tanks appeared intact and contained fuel. A postaccident on-scene examination of the airplane did not reveal any anomalies attributable to a preimpact failure or malfunction. FAA records indicate that the pilot was issued a student pilot certificate on July 25, 2012; however, there was no record of the pilot having been issued an airman medical certificate. He could not provide any record of an endorsement for solo flight as required by the regulations. The pilot informed FAA inspectors that he did not maintain a flight time logbook. However, he reported accumulating about 300 hours total flight time, with about 30 hours in Sparrow II airplanes. The pilot also informed inspectors that he had been involved in previous accidents that had not been reported to the FAA or NTSB. The accident airplane was issued an experimental airworthiness certificate in October 1998. The pilot bought the airplane in April 2012. However, FAA records indicated that the pilot did not submit the required documentation to transfer the registration. The airplane registration was subsequently cancelled on September 3, 2014. The pilot informed FAA inspectors that he did not maintain any maintenance logbooks for the aircraft. Although the pilot reported maintaining the airplane himself, there was no record of the pilot holding a mechanic or repairman certificate.