On July 26, 1999, about 0830 Eastern Daylight Time, a homebuilt Pietenpol, N6286A, was substantially damaged during a forced landing at Collins, Ohio. The certificated private pilot and passenger were not injured. Visual meteorological conditions prevailed for the flight that originated from a private grass airstrip at Valley City, Ohio; destined for Wood County Airport, Bowling Green, Ohio. No flight plan was filed for the personal flight conducted under 14 CFR Part 91. During a telephone interview, the pilot stated that he was in cruise flight approximately 2,000 feet mean sea level. The engine lost all power, and he made a forced landing to a soybean field. During the landing, the left main landing gear folded under the airplane, and the right wing spar fractured. He added that examination of the wreckage revealed four bolts, which secured the propeller, were sheared. The respective four nuts and propeller were not recovered. The pilot believed that fatigue caused one bolt to shear, and a subsequent vibration occurred. The vibration caused the remaining bolts to shear. On this particular airplane, the propeller acted as a flywheel. The pilot stated that the absence of a flywheel would cause the engine to stop. When asked why he believed the bolts failed, the pilot stated: "After studying the prop hub on this plane, it is clear that this hub, that was designed in 1929, is not strong enough. I think that the outside cover plane on the propeller should be keyed to the propeller shaft to remove any twisting of the propeller bolts." The pilot last secured the propeller to the airplane approximately 1 year before the accident. Since then, he estimated that the airplane flew approximately 40 hours. According to the Safety Board's database, from January 1, 1989, through August 12, 1999, there was one other documented case of a propeller bolt failure on a Pietenpol (CHI92DEX04). However, the pilot stated that he knew of another Pietenpol owner that had a similar occurrence.