On June 29, 1995, at 1630 central daylight time, a Cessna 172RG, N9502D, was substantially damaged after impacting a wire near Weston, Texas. The flight instructor and a commercial pilot receiving instruction were not injured. Visual meteorological conditions prevailed for the 14 CFR Part 91 instructional flight. According to the operator, the flight departed the Addison Airport at 1520 on an instructional flight in preparation for a certified flight instructor (CFI) check ride. After executing a simulated forced landing to an open field, the airplane struck a power line 25 feet above the ground while recovering from the simulated emergency. Neither pilot reported seeing the wire prior to impact. The commercial pilot flying reported losing rudder effectiveness after impact with the wire. The instructor pilot elected to take the controls of the aircraft and flew to a nearby airport, where he made a successful precautionary landing. Examination of the airplane revealed that the top 6 inches from the rudder and vertical stabilizer had separated.