On January 16, 1994, about 1400 eastern standard time, a Boeing A75N1, registered to the Stearman Flight School, Inc., crashed about 1/2 mile west of the runway at the Bob White Airport, Zellwood, Florida, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The airplane was substantially damaged and the commercial pilot, the sole occupant, sustained serious injuries. The flight originated about 1330 from the Bob White Airport, Zellwood, Florida. The pilot stated that he had performed at least four touch-and-go landings and after takeoff following the fourth, he turned left crosswind, then downwind. The flight climbed to a higher than standard altitude to execute a commercial spiral to land maneuver. Witnesses reported that the airplane climbed to about 1,500 feet during the downwind leg. The pilot further stated that he initiated the spiral for landing but is unsure how many turns he completed;however, he recalls turning left base in a 45-degree bank. He added power after realizing that the airplane was low and applied control input to stop the turn but the descending turn continued. The airplane impacted the ground nose and left wing low and came to rest upright. Examination of the airplane by an FAA inspector revealed that the right rudder horn was failed. Additionally, the rudder stops were inspected and found to be installed. Examination of the flight control system revealed no evidence of any other pre impact failure or malfunction. The failed rudder horn was removed from the airplane for metallurgical examination by the NTSB metallurgy laboratory. Metallurgical examination of the fracture surfaces of the rudder horn revealed that it failed due to overload. There was no evidence of preexisting failure.