On September 17, 1998, at 1150 central daylight time, a Piper PA- 22-108, N4749Z, operated by a private pilot touched down short of runway 13 at the Rock County Airport, Janesville, Wisconsin. The pilot was not injured. The airplane was substantially damaged. The 14 CFR Part 91 personal flight was operating in visual meteorological conditions without a flight plan. The flight originated from Schaumburg, Illinois, at 1100 cdt. The pilot reported that he was cleared to enter a right traffic pattern for runway 13 when he was about 15 miles away from the airport. He reported that on short final, at an altitude of about 60 feet above the ground, with the engine set at 1500 rpm, the airplane started to sink. The pilot reported he applied power, but the airplane continued to sink. The airplane contacted the terrain short of the approach end of the runway. The nose wheel contacted the top of a 25-foot ditch which resulted in the nose gear collapsing. Local winds at the time of the accident were reported as being from 110 degrees at 6 knots.