The aircraft arrived at Cheyenne, Wyoming at 00:38 on a Civil Air Movement flight from New York International Airport. The aircraft departed Cheyenne at 01:32, on an instrument flight plan to Chicago at 7,000 feet. The C-46 progressed uneventfully until it reached Omaha. The pilot contacted Omaha INSAC and requested a change of altitude to 3,000 feet. This was denied because another flight proceeded at 2,600 feet between Des Moines and Omaha. The aircraft flew then into a severe thunderstorm in the vicinity of Des Moines. The aircraft lost control and subsequently the right wing panel failed at the attach angles to the center section due to a strong downward force which exceeded the design strength of the wing. The wing panel then struck the tail, causing it to disintegrate. PROBABLE CAUSE: “Separation of the right aileron tab motor from its support bracket due to loss of its outboard trunnion while the aircraft was in the severe turbulence of a thunderstorm. These conditions resulted in a tendency to roll erratically, and in conjunction with the extreme turbulence, caused loss of control and subsequent overloading of the wing to the point of failure.”