What happened
Following takeoff, the pilot observed the airplane yawing to the left and noted fluctuations on the left engine torquemeter. In response, the pilot feathered the left engine and initiated a turn back toward the airport.
During the return, the pilot maintained a flap setting of 20 degrees, which resulted in a climb performance that did not exceed 200 feet AGL. The pilot reported an airspeed of 115 knots, which was below the manufacturer's recommended minimum of 140 knots for such configurations.
The pilot decided to land on the departure runway, approaching from the opposite direction of takeoff. The approach involved a 90-degree angle to the runway centerline, followed by a 90-degree turn to align with the runway. To reach the runway, the pilot delayed the extension of the landing gear. Upon extending the gear, the airplane entered a stall and touched down before the landing gear had reached the 'down and locked' position. This caused the gear to collapse, resulting in the airplane sliding off the runway.
No injuries were reported.