On May 22, 1996, at 1015 hours mountain standard time, a Rotorway Exec 9 experimental helicopter, N89678, turned over during a normal approach to landing at Chandler, Arizona. The aircraft sustained substantial damage and the two pilots onboard were not injured. Visual meteorological conditions existed at the time and no flight plan was filed for the local instructional flight. According to the instructor pilot, he set up for a normal landing into the wind from an altitude of 500 feet agl. He began an application of power at 40 feet agl when the main rotor rpm needle entered the yellow (arc). With a full application of power, the rpm continued to the lower portion of the yellow arc. The helicopter made ground contact with low rotor rpm. The aircraft yawed to the right and the pilot applied full right pedal. On initial ground contact the right skid collapsed and the aircraft bounced, turned, and rolled over. The pilot reported a left quartering wind at the time. The pilot stated the terrain was flat and level, and he had used this landing site before. He reported no mechanical malfunctions with the aircraft prior to the accident. The engine was examined and a report was submitted from Rotorway International. They reported that the upper edge of the number 1 piston (approximately 1/8 of its diameter) was broken away down to the top of the piston ring groove. The upper ring was broke and pieces were found in the combustion chamber. They reported there were no signs of the ring or piston in the cylinder and that all pieces had exited the exhaust port. The report further states that carbon build up on the cylinder sleeves above the top ring surface was normal except in the area of the piston breakage. To them, this indicated the engine was operating for some time before the damage had been noticed. Also, the cylinder was found out of round beyond normal specifications.