The 1,769-non-instrument rated private pilot and his passenger departed from a nearby private airstrip approximately 1130 and proceeded to a motor park racetrack that was under construction. The landing on the 1,800-foot long hard packed dirt strip was uneventful. After spending 40 minutes to an hour at the construction site, the pilot and his passenger boarded the 1967-model tailwheel-equipped airplane for the return trip. The pilot again utilized the 1,800-foot dirt strip for departure on an easterly direction. As the airplane was departing, the pilot reported in the Pilot/Operator Aircraft Accident/Incident Report (NTSB 6120.1) that the airplane "became uncontrollable due to unknown causes." Examination of the airplane by a Federal Aviation Administration (FAA) inspector, who responded to the accident site, revealed that the airplane's right wingtip collided with a parked minivan and the airplane cart-wheeled several times before coming to rest in an inverted position near a steep embankment. The pilot, who was occupying the front seat, was extracted from the airplane by fire-rescue personnel with the aid of the "jaws of life." The passenger on the aft was able to egress the airplane unassisted and suffered minor injuries. A person on the ground that was standing by the parked vehicle was also injured. The pilot reported that he had no recollection of the flight or the ensuing accident. At 1253, the automated surface observing system at the nearest airport, located about 10 miles southeast of the accident site, reported clear skies and wind from 050 at 7 knots.