Substantiation by Analysis for Fatigue Tolerance in Bell 525 Metallic Components

The Bell 525 main rotor Pylon Bipod Mount is a flight critical structural component that must meet the fatigue tolerance requirements of §29.571. The complex flight load environment of the Pylon Bipod Mount involves coupling the rotor loads to the fuselage through interactions that factor roof beam displacement and the unique stress state induced by the elastomeric inner member of the Bipod. Simulating the full flight load structural response of the Bipod in a physical component test is not only extremely time consuming but also runs the risk of being inaccurate. As an alternative, an experimentally correlated finite element model is used to analyze the Bipod under the flight load environment. The approach incorporates the installation stress on the Bipod induced by its elastomeric component. The associated finite element models will be validated using state of the art experimental techniques of strain survey/mapping. Results from the correlated analytical models will be further evaluated per approved regulatory criteria to substantiate the Bipod's fatigue life and demonstrate fatigue tolerance per §29.571.