On July 16, 1996, at 0720 central daylight time, a Stol UC-1, N9507U, registered to and operated by a private owner under Title 14 CFR Part 91, was substantially damaged during a forced landing near Princeton, Texas. The airline transport rated pilot and his pilot rated passenger were not injured. Visual meteorological conditions prevailed for the cross-country flight and a flight plan was not filed. The flight originated from Gladewater, Texas, at 0610, and the intended destination was Childress, Texas. According to the pilot, the airplane was in cruise flight at 4,500 feet MSL when the left engine propeller "went into feather, causing the engine to stall." The pilot's attempts "to unfeather the propeller and restart the engine" were unsuccessful. The pilot reported that "the aircraft's single engine performance was inadequate to maintain altitude." A forced landing was made to an open field with the landing gear up. During the landing roll, the airplane impacted a drainage ditch, resulting in substantial damage to the right lift strut and the fuselage. The accident flight was the continuation of a trip which started on July 13, 1996, in Hollywood, Florida, with a planned final destination of Lake Havasu City, Arizona. The pilot had purchased the airplane in Florida and was flying it to his home in Arizona. According to the pilot, "through-out the entire flight (7-13 to 7-16)," he "had difficulty keeping the props in synch." He further stated that "the longest period of time they would remain synchronized was approximately one minute." Both the pilot and the passenger held mechanic certificates with airframe and powerplant ratings. The left engine propeller governor was removed and bench tested under the supervision of an FAA inspector. The manufacturer's specifications called for the feather stop on the governor to be set at 1,690 rpm. Testing revealed that the stop was set at 2,000 rpm.