On August 15, 1998, at 1455 central daylight time, a Whetzel Thorpe T-18 (amateur built airplane), N60LW, sustained substantial damage when it exited runway 27 (5,000' X 75' dry/asphalt), and nosed over, near Rantoul, Illinois. The pilot said that he lost directional control. The pilot reported minor injuries. The personal 14 CFR Part 91 flight was operating in visual meteorological conditions. No flight plan was on file. The flight departed Vernon, Ohio about 1400. In his written statement the pilot said that during rollout, the airplane drifted to the left edge of the runway. He said that he applied full throttle attempting to abort the landing; however, he was unable to control the airplane as it exited the runway into a crop field and nosed over. The airplane was examined after the accident and no pre-accident anomalies were found. The flight controls revealed continuity and the brakes operated.