The pilot reported that at about 50 knots during the take-off run, he heard a loud noise and the aircraft began to progressively adopt a nose low attitude. The nose of the aircraft dug into the ground and the aircraft overturned. When the pilot inspected the aircraft following the accident, he found that the landing gear was retracted and that the gear selector was in the up position. The pilot did not recall the position of the selector before the commencement of the take-off. Inspection and testing of the gear system failed to reveal any fault that could have contributed to this accident. It is considered possible that the gear lever was not correctly positioned in the down detent prior to the takeoff being commenced. It is then likely that during the takeoff run the lever worked its way towards the up position and that the gear began to retract when the weight of the aircraft was taken off the gear as the aircraft ran over a hump in the strip.
