During the preflight inspection, a small amount of hydraulic fluid was noticed by the trim wheel. In order to troubleshoot the problem, maintenance personnel removed the left front pilots seat and then reinstalled it when the problem was resolved. During the takeoff roll, after adding full power, the pilots seat abruptly slid to the full-back position, resulting in the airplane veering sharply to the left as the pilots feet left the rudder pedals. In an attempt to avoid hitting signage, the pilot lifted off, but then he heard something strike the airplane. Airborne, the pilot managed to get the seat forward, climb to pattern altitude, and land uneventfully. After securing the airplane the pilot noticed that the left front seat had not been reinstalled in the seat rail, but was resting on top of it. Damage to the airplane consisted of a propeller strike, a hole in the undercarriage, and damage to both horizontal stabilizers.
