The mid-wing configured experimental airplane was observed flying close to the runway surface. Witnesses reported the airplane executed a steep climbing 360 degree turn to the right. The airplane stalled at the conclusion of the turn and descended into trees adjacent to the runway. An on-scene investigation revealed the builder of the airplane was also the pilot. The builder had deviated from the designer's plans and modified the rudder control system. The result of the modification was a left rudder cable failure due to chafing and overload. The builder had also installed an engine which had 25 horsepower (hp) more than allowed by the designer. The designer stated an airplane with 65 hp would perform too steep a climb for the average person. This, he stated, would cause the pilot to lose reference with the horizon due to the airplane's mid-wing configuration. The designer also stated the mid-wing configuration does not block airflow over the elevator unless in a stall, at which point the turbulent air would pass over the elevator.