On January 1, 2003, at 1555 central standard time, a Wood Thorp T-18 tailwheel-equipped homebuilt airplane, N335BW, was substantially damaged upon collision with terrain following a loss of control while attempting to takeoff from the Clark Field Municipal Airport (SEP), near Stephenville, Texas. The instrument-rated private pilot sustained serious injuries and his pilot-rated passenger received minor injuries. The airplane was owned and operated by the pilot, who was also the builder of the airplane. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 91 personal flight for which a flight plan was not filed. The 220-nautical mile cross-country flight was originating at the time of the accident, and was destined for the Baytown Airport (HPY) near Baytown, Texas. In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the 647-hour pilot, 292 hours of which were in the accident airplane, reported that he applied full power slowly, holding back pressure on the controls until the airplane became airborne. During the transition from back pressure to forward pressure a gust of wind came from the west. The pilot was unable to compensate for the left crosswind in a timely manner to maintain directional control of the airplane. The airplane became airborne after cresting the top of a berm on the east side of the runway, and landed hard on the far side of the berm, spreading the landing gear. The landing gear pointed toward each wing tip, but the airplane was still progressing forward, dragging the landing gear. The landing gear "hung up" on with the ground and the airplane came to a sudden stop, nosed over, and came to rest in the inverted position. The pilot's sister witnessed the accident, summoned for help, and was the first responder to the accident site. Local fire department and EMS personnel arrived at the accident site. Airbags were used to lift the airplane and the canopy was removed to facilitate the extraction of the two injured occupants. According to witnesses at the airport, the pilot lost directional control of the airplane during the initial takeoff roll from Runway 32. Runway 32 was reported to be a 4,200 feet long by 75 feet wide asphalt runway. An FAA inspector, who responded to the accident site, reported that the canopy was crushed, the propeller was damaged, and both wings sustained structural damage. No anomalies were noted with the airframe or the 160-horsepower Lycoming IO-320-B1A engine. The nearest weather reporting station is located at the Mineral Wells Airport (MWS), which is located 34-nautical miles north of SEP. At 1453 the weather station at MWS reported winds from 290 degrees at 17 knots, gusting to 24 knots. The peak winds were reported from 270 degrees at 27 knots.