On August 31, 2002, approximately 0920 Pacific daylight time, an amateur-built experimental-category Nolley BD-5 airplane, N50TX, was substantially damaged in a forced landing in a field approximately 1 1/2 miles southeast of the Corvallis Municipal Airport, Corvallis, Oregon, following a reported partial loss of engine power during climb after takeoff. The private pilot, who owned and had built the single-seat aircraft, received serious injuries in the forced landing. Visual meteorological conditions were reported at Corvallis at 0935. No flight plan had been filed for the local 14 CFR 91 personal flight, which departed Corvallis Municipal about 0900. According to the FAA aircraft registry, the accident airplane received initial experimental-category airworthiness certification on June 19, 1998. The aircraft was equipped with a 95-shaft horsepower Quantum turboprop engine, a conversion based on components of the Solar T-62 power system. A witness to the accident, who reported that he was a co-builder of the accident airplane and stated he witnessed the accident from a chase aircraft, reported that the accident flight was part of the accident aircraft's initial required 40-hour flight test period, with 16.8 hours on the aircraft's Hobbs meter at the time of the accident. The witness reported that the objective of the accident flight was to determine the aircraft's stall characteristics pursuant to the 40-hour flight test period. The witness reported that after takeoff, the pilot reported to him on the radio that he was not able to climb higher than traffic pattern altitude (approximately 1,000 feet above ground level). The witness stated that the aircraft completed about two circuits around the airport when it suddenly pitched over and subsequently impacted the ground in a level attitude, coming to a stop in 100 to 125 feet and pivoting about 90 degrees to the left. During a telephone conversation with an investigator from the NTSB, the pilot reported that the airplane began to lose power shortly after takeoff from the Corvallis Airport. He reported that he was unable to restore engine power and elected to perform an off-airport landing to a nearby open field. He reported that the airplane touched down hard and the gear collapsed. He also reported that he was unable to recall any specific engine instrument readings or warning lights in the cockpit before, during or after the power failure. The initial onsite investigation was conducted by an inspector from the Portland, Oregon, Flight Standards District Office (FSDO) on the day of the accident. During the examination the inspector noted that the left main fuel supply line, at the quick connect coupler, was disconnected. No damage was noted to the fuel line or associated coupler. On November 25, 2002, a test run of the accident aircraft's converted Solar gas turbine engine was conducted at Apex Gas Turbines, Silverdale, Washington. The test was conducted with the engine mounted on a test stand. The engine was successfully started and run at multiple power settings. No operating malfunctions or anomalies were noted during the test run.