On January 17, 1998, at 1500 central standard time, a Christopher Coats, Challenger II Experimental airplane, N132BC, collided with the ground during an emergency landing near Evergreen, Alabama. The personal flight operated under the provisions of Title 14 CFR Part 91 with no flight plan filed. A review of weather data recovered from the nearest reporting facility, disclosed that visual weather conditions prevailed at the time of the accident. According to the pilot, the airplane received substantial structural damage. The private pilot was not injured. The flight departed Brewton, Alabama, at 1430. The pilot reported that, while cruising at 1200 feet, and about thirty minutes into the flight, the "engine began to speed." When the pilot reduced the throttle, he noticed that the propeller assembly had separated from the engine. The pilot selected an emergency landing area on Interstate 65.near mile marker 92.2. As the pilot maneuvered for an emergency landing on the heavily traveled highway, the right wing collided with an overpass bridge. The pilot stated that the collision occurred as he attempted to fly under the bridge. An examination of the airframe, at the accident site, confirmed that the propeller assembly had separated from the engine assembly. During the examination of the airframe, it was also noted that the six propeller retention bolts were not present with the engine. The propeller assembly and the six propeller retention bolts were not recovered for metallurgical analysis. According to the pilot, he assembled the airplane in accordance with the kit instructions. The propeller assembly was installed on the engine and secured with six 5/16 inch coarse threaded bolts provided in the kit. He further stated that the propeller retention bolts were tighten to ten foot pounds of torque.