On May 2, 2018, about 1100 central daylight time, an experimental, amateur-built Kitfox III airplane, N73BH, was substantially substantial damaged during a forced landing after takeoff from the Stovall Ranch Airport (6TX9), Marathon, Texas. The airline transport pilot and one passenger sustained minor injuries. The airplane was privately owned and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed throughout the area and no flight plan was filed for the flight. The local flight was originating at the time of the accident. The pilot reported that during takeoff, about 15 ft above the ground, the airplane rolled violently to the right. He applied full aileron and rudder opposite the direction of the roll, but the airplane continued to roll to the right. The airplane struck the ground with the right wing and then impacted a mesquite tree. Examination of the wreckage after the accident revealed that 3 of the 4 hinges connecting the right flaperon hangar rib were loose. The wooden (spruce) material of the flaperon appeared to by dry rotted where the hinges attached. According to records provided by the owner, the airplane had last flown about 6 months prior to the accident flight. Records showed that the airplane had about 3 hours of flight time since its most recent conditional airworthiness inspection which was performed on May 23, 2017. Denny Aerocraft Company Service Bulletin #9, dated September 12, 1991, had identified flaperon hangar rib failures on Kitfox models I, II, and III. The service bulletin recommended the addition of an aluminum reinforcement on each flaperon hanger rib end. The accident airplane did not have the reinforcement installed.