On June 25, 1996, about 1700 eastern daylight time, a Aeronca 7AC, N84538, registered to a private owner, sustained damage when the right main gear collapsed during a forced landing in a field near Callahan, Florida, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the commercial-rated pilot was not injured. The flight originated from Jacksonville, Florida, the same day about 1630. The pilot stated that while in cruise flight at 1,200 feet, the engine began to run rough. The engine oil pressure and oil temperature were normal. He applied carburetor heat and the engine roughness got worse. He immediately selected a field and began his approach to the field for a forced landing. While approaching the field he observed fence posts in his path and extended the approach to avoid them. After touchdown he turned the aircraft to the left in an attempt to spin the aircraft around and stop. The right main landing gear hit something, collapsed, and folded under the aircraft. The aircraft slid to a stop. After the accident the engine was started in the presence of an FAA inspector and operated to full power with no evidence of failure or malfunction. The carburetor heat operated normally. Carburetor icing probability curves indicate the aircraft was operating in conditions conducive to visible icing at glide and cruise power at the time of the accident.