On December 24, 1998, at about 1045 eastern standard time, a Dean, Kolb Firestar 1, N643FS, registered to a private owner, operating as a 14 CFR Part 91 personal flight, experienced a loss of directional control on climb out from the Gore Airport, Davenport, Florida, and collided with trees. Visual meteorological conditions prevailed and no flight plan was filed. The airplane sustained substantial damage. The private pilot reported no injuries. The flight originated about 1 minute before the accident. The pilot stated he has not flown in about 3 years, and that he did not have a current medical certificate. He completed two high speed taxis up and down the runway before departing for takeoff to the east. Once he became airborne the airplane started veering to the right. He lost directional control, and the airplane collided with trees and terrain. The pilot stated examination of the airplane revealed no evidence of a mechanical failure or malfunction. The pilot told the FAA that he had experienced a substantial weight loss since he last flew the airplane. According to weight and balance information produced from the aircraft blue prints, the pilot calculated that he was outside the aft center of gravity limit at takeoff, which resulted in the loss of directional control. Review of the pilot's total flight time entered in the NTSB Pilot/Operator Aircraft Accident Report revealed that he had not recorded as logged any flight time in the Kolb Firestar 1 experimental airplane.