The airplane was substantially damaged during a forced landing at about 1000 Central time, following a loss of engine power after takeoff. The solo airline transport pilot sustained minor injuries. Visual conditions prevailed. Shortly after takeoff, the engine began to “run rough, as if it had a fouled plug.” While turning to downwind the engine began to “shake violently,” and RPM and altitude were decreasing. The pilot selected a field and performed a soft-field landing, during which the airplane nosed over and came to rest in an inverted position. The pilot was able to exit the airplane unassisted. Moments later the airplane was engulfed in flames.