On July 5, 1994 at 1800 central daylight time, an experimental Parson-2P gyroplane, N589RH, was substantially damaged during landing at Monmouth Airport, Monmouth, IL. The private pilot sustained minor injuries. Visual meteorological conditions existed at the time of the accident. The local flight, conducted under 14 CFR Part 91, originated 5 minutes prior as part of the 40 hour flight test period. The pilot reported that after reaching an altitude of 100 feet he turned right to avoid going over highway I-34 and the city of Monmouth, IL. The aircraft began losing altitude, with no power loss. He found a clear area along the runway. Upon landing, the right wheel struck a hole causing the aircraft to shake violently. The aircraft came to rest on its right side, sustaining substantial damage. According to the pilot logbook, he had a total of 28.3 hours flight time in gyroplanes, and was first endorsed for solo flight on July 22, 1993. He stated that this was his first flight since December 1993. The aircraft sustained substantial damage. No fire or explosion occurred. The right main wheel, engine propeller, main rotor blades, center line keel and main rotor head support brace were damaged. The pilot holds a private pilot certificate, airplane single engine land ratings with a student pilot endorsement for gyrocopter.