The pilot of the amateur-built Junior Ace stated that the purpose of the personal flight was to fly in the local area for about one hour. The airplane was equipped with one centrally-mounted control stick, a two-place bench seat, and two sets of rudder pedals. About 20 minutes into the flight, the pilot turned the airplane to the left. When he attempted to turn to the right, the airplane yawed "uncontrollably" to the left. The pilot said he applied more right rudder in an attempt to control the left yaw, but the yaw increased. The pilot reported that he could not stop the yawing motion. He stated that, "it felt like the airplane was stalling and about to spin." A witness stated that the airplane's wings rocked back and forth in a smooth, slow, rocking motion. The pilot attempted to land in a field, and "flared high" above the ground. The airplane impacted the ground and nosed over. The right main landing gear, right wing rear strut, and firewall were damaged. The pilot reported that there were no mechanical malfunctions of the airplane prior to the flight. He also stated that for this flight he sat in the center of the bench seat, straddled the control stick, and was using the "outboard rudder pedals." Examination of the wreckage by a Federal Aviation Administration inspector revealed all flight controls moved freely and had full travel.