While the pilot was conducting a fast taxi test, the experimental airplane that he had been rebuilding for almost 2 years, unexpectedly became airborne. The pilot's intent was not to fly. There was not enough runway remaining to land safely so the pilot decided to continue flying the airplane about 5 miles to an airport that had multiple long runways and to try to land. He flew the airplane in a large circle trying to get the feel for the controls so he would be better prepared to land. There was a 10-pound sandbag in the rear seat that the pilot used to lay on the front canard when the airplane was parked. He said that the weight helped the airplane from tipping over backward when the motor was not running and no one in the cockpit. He said that he intended to buckle the sandbag in prior to the taxi test, but did not. While circling for a long final approach, the elevator froze and the airplane pitched down. The pilot could not move the control stick rearward to arrest the descent. He tried everything to release the control jam including putting so much back pressure on the control stick that it bent, still with no change. He saw wires approaching and was hoping that he would clear them, but the airplane hit the wires in the middle of the lines. Both wings came off and the airplane caught fire and fell straight down, about 50 feet. After impact, three men appeared and freed the pilot from the burning airplane. The pilot later looked at the burned out fuselage and confirmed that the sandbag was where he thought it had ended up, between the back seat and the rear control stick. He said that he should have taken the time to secure the sandbag prior to the taxi test.