On August 1, 1993, at approximately 1300 central daylight time, a Stinson 108-3 airplane, N4021C, sustained substantial damage near Osceola, Arkansas, during approach. The private pilot and passenger were not injured. Visual meteorological conditions prevailed for the personal cross country flight. The Pilot/Operator report submitted to the Safety Board and a personal interview conducted by the investigator in charge revealed the following information. During a cross country flight a routine refueling stop was made at Osceola, Arkansas. As the air speed increased during the initial takeoff climb, the right half of the engine cowling came loose. The pilot observed the engine cowling chaffing against the windshield plexiglass. A 180 degree turn toward the airport was initiated by the pilot. During the approach, the airplane stalled and impacted the terrain short of the runway. The pilot stated that he had checked and filled the engine oil and had improperly latched the cowling during the preflight.