Application of an Empirical Fatigue Design Method to Predict Fatigue Life During a Development Program

During development testing, preliminary loads data and S-N data became progressively more complete. On the YAH-63, all new data were used at it became available to systematically update life predictions, to identify problem areas and initiate design changes. The method by which this was accomplished is an extension of "A Simplified Empirical Method for Rotor Component Fatigue Design," presented at the 25th Annual AHS National Forum by Mr. G. L. Graham. This method was developed from numerous fatigue life calculations on a number of helicopter models to meet design objectives. Using this empirical method to predict life during testing is a new application of the original concept, providing a fast, rational method for systematically updating component fatigue life estimates. Based on these estimates, any parts indicating a need for redesign are found early in the development cycle and appropriate action can be taken.