The pilot stated that she was conducting touch-and-go takeoffs and landings. During the last touch-and-go landing, she retracted the flaps and applied full throttle. The ground roll seemed slightly longer than previous takeoffs. After liftoff, the airplane was not climbing and the pilot thought that it was developing less than full power. As the airplane was approaching power lines, the pilot felt that the airplane would not clear them so she elected to land on a field. The airplane impacted the ground during the landing and sustained substantial damage, which included a damaged left wing, a ruptured fuel tank, and a deformed fuselage. Postaccident examination of the airplane revealed that the airplane cockpit flap indicator was in the 20-degree position. No preexisting mechanical anomalies were noted with the airframe, engine, or engine accessories that would have precluded normal operation. According to the aircraft’s Pilot Operating Handbook, “Normal takeoffs are accomplished with wing flaps 0°- 10°. Using 10° wing flaps reduces the total distance over an obstacle by approximately 10%. Flap deflections greater than 10° are not approved for takeoff.”