20230810014069A

The pilot reported, in a written statement that he was attempting to give his student training on proper rudder application during takeoff. He decided it would be beneficial for the student to practice high speed taxis down the runway at Yuba County Airport (kmyv). Prior to the flight, the pilot reviewed performance charts and determined the ground roll to stop distance to be 520 feet based on the current weather. He decided they would abort the maneuver at 1,000 feet prior to the end of the runway and their goal airspeed would be less than 60 mph. The pilot and his student landed at kmyv, made appropriate radio calls, then decided to back taxi on the runway at a high speed. The instructor stated he was focused on the runway distance and not the aircraft speed. The aircraft was not lifting off the ground, so he assumed they were below lift off speed when in fact the aircraft was over 80 mph. At the 1,000 foot mark on the runway, the instructor told the student to bring the power to idle and apply brakes. The aircraft failed to slow to the instructor’s satisfaction, so he decided to take off and applied full power to the aircraft. The aircraft went off the end of the runway into the gravel before becoming airborne. The tail of the aircraft impacted a runway end light before flying to auburn municipal airport (kaun). Substantial aircraft damage caused by impact points on the underside of the fuselage and the underside of the right wing. Aircraft and engine were both operating as expected at the time of the accident.