On September 1, 2007, about 1546 mountain standard time, an experimental Wessel Vortex, N546SW, made a forced landing in rough terrain about 4 miles north of the Falcon Field airport, Mesa, Arizona. The private pilot was the owner and operator of the homebuilt gyrocopter, and it was substantially damaged upon rolling over during impact with 5-foot-high brush in a ravine. The pilot was not injured. Visual meteorological conditions prevailed at the time, and no flight plan had been filed. The personal flight was performed under the provisions of 14 CFR Part 91, and it originated from Mesa about 1445. The pilot reported to the National Transportation Safety Board investigator that during cruise flight he heard a loud noise and felt a vibration. Thereafter, the rotorcraft lost power when one of the pusher propeller blades separated, and he autorotated. The pilot additionally reported an examination of the engine assembly revealed that the muffler's mounting strap had failed, and this event resulted in the subsequent separation of one composite propeller blade.