Fail Safe Evaluation of Helicopter Structures

The paper presents a fail-safe evaluation of a part of CH-47 helicopter structure. The FE model of the helicopter fuselage was modified to account for the worst damage scenario. The frames in the affected area were assumed to contain discontinuities. Margins of safety were calculated for the frames and skin panels using “B” - basis design allowables. The reduction of allowables due to the temperature was determined and applied for the analysis. The results show redistribution of forces to the adjacent structure. The margins of safety remained positive, showing ability of structure to withstand a significant damage in a highly loaded area. Tables and graphs showing margins of safety of the original and damaged configuration are presented. Discussion of the assumptions and the methods employed is presented. The procedure allowed to substantiate analytically ability of structure to redistribute the loads in the vicinity of damage and an application of fail-safe methodology for a helicopter structure.