On July 9, 2000, about 1820 Eastern Daylight Time, an Ercoupe Forney F-1, N7518C, was substantially damaged during an off airport precautionary landing near Leechburg, Pennsylvania. The certificated private pilot and passenger were not injured. Visual meteorological conditions prevailed and a visual flight rules flight plan had been filed for the flight that departed Kent, Ohio, destined for the Montgomery County Airpark Airport, Gaithersburg, Maryland. The personal flight was conducted under 14 CFR Part 91. According to the pilot, approximately 1 hour and 15 minutes after takeoff, while in cruise flight at 5,500 feet (msl), he experienced smoke in the cockpit and noticed the engine oil pressure had dropped to zero. The pilot noted that the nearest airport was about 9 miles from his position; however, he elected to make a precautionary landing to a grass field. During the approach, the pilot realized the airplane's approach speed was too fast to touchdown on the grass field, and he performed a landing to an adjacent corn field. During the landing, the airplane's left wing and empennage were damaged. Examination of the airplane by a Federal Aviation Administration inspector revealed the airplane's engine oil pressure line was severed about 1/16 of an inch from the nut that attached the line to the engine block. Oil was found in the engine compartment and streaks of oil were observed on the right side of the fuselage. Additionally, only about 1/2 of a quart of oil remained in the engine's oil sump. No other discrepancies were noted.