On July 16, 2001, about 1830 eastern daylight time, a Rans S-12, N40R, was substantially damaged during a forced landing near Waldorf, Maryland. The certificated private pilot was seriously injured, and the passenger was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight conducted under 14 CFR Part 91. According to the pilot, he was in cruise flight over Waldorf, en route to a private landing strip. As he made a turn, the engine suddenly lost all power. A forced landing was performed to a construction site, and the airplane touched down hard, coming to rest upright. A witness, who was working at the construction site, stated that he observed the airplane flying over some trees and the engine did not sound like it was developing power. The pilot stated that he had completely fueled the airplane prior to departing on the accident flight, with fuel cans that he had in the garage; however, he could not recall how old the fuel was, or when the last fueling of the airplane took place. The pilot estimated that the wing tanks were filled "half way" prior to the fueling. The pilot additionally stated that the airplane was constructed with "flat" fuel tanks. The fuel tanks were not equipped with fuel sump drains, and the only means of assuring the fuel was absent of contamination, was a sump drain located on the manifold, which provided fuel to the engine. The pilot reported that no recent maintenance had been performed on the airplane or engine, and it was "running fine" prior to the accident. A Federal Aviation Administration inspector examined the airplane after the accident and observed fuel in the lines and carburetor bowl. The inspector could not conduct a test run of the engine due to impact damage. According to a representative of the airplane kit manufacturer, the kit was produced with two flat fuel tanks, which included withdrawal points located on the front and back of the tanks. Fuel lines from both wing tanks were then routed to a "mixer block," which was located about 2 feet below the tanks. A valve, located on the "mixer block," enabled the pilot to drain fuel and check for contamination. The representative added that it was at the discretion of the kit builder to install sump drains at the low point of the wing fuel tanks, and they did not provide any guidance on preflight procedures.