Abstract
The lower wing section of an aircraft is considered particularly vulnerable to fatigue failure due to the presence of inspection holes, which create stress concentrations and increase local stress in the surrounding material. This study estimates the fatigue life of the lower wing structure, including rivet holes around the inspection openings, in a new-generation Indonesian short takeoff and landing (STOL) aircraft under cyclic flight loads. Fatigue assessment was conducted in five stages: (1) development of a 3D design model of the lower wing skin; (2) stress analysis of the skin without rivet holes, using finite element analysis (FEA), to identify critical areas around the inspection hole; (3) stress analysis of the skin with rivet holes in these critical areas; (4) compilation of a stress spectrum from flight test data; and (5) fatigue life estimation using the cumulative damage method with the application of a scatter factor. The analysis results indicate a maximum fatigue life of 67,750 flight cycles for rivet holes in the lower wing skin, exceeding the industry target of 30,000 cycles. However, when a scatter factor is applied, the maximum fatigue life is reduced to 13,550 flight cycles, establishing the required inspection threshold for the STOL aircraft.