On July 8, 1999, at 1915 central daylight time, a LET Blanik L-13, N3209F, piloted by a commercial flight instructor, received substantial damage during an on-ground collision with two trees while landing on Runway 26R (2,360 feet by 120 feet, dry/turf) at the Sylvania Airport, Sylvania, Wisconsin. Visual meteorological conditions prevailed at the time of the accident. The local instructional flight was operating under the provisions of 14 CFR Part 91 and was not on a flight plan. The Certified Flight Instructor (CFI) and dual student reported no injuries. The flight departed the Sylvania Airport at 1845 and was landing at the time of the accident. The CFI reported that she was demonstrating a landing approach without the use of dive-brakes. The CFI stated that that the glider landed long and during the landing roll it became evident that the aircraft would not stop before the end of the runway. The CFI reported that in order to avoid overrunning into a corn field, at the end of the runway, she deployed the dive-brakes, and turned the aircraft to the right towards an open flat field. The aircraft impacted between two trees on the right side of the runway. Inspection of the wreckage revealed no pre-accident flight control anomalies.