Development of an on-board fatigue processor for helicopters

Abstract

An on-board fatigue processor was developed for helicopters. This processor can provide a continuous monitoring of fatigue usage of rotating mechanical components during flight using only standard flight control data as input. The monitoring methodology used in the fatigue processor reduces a complex load time-history into two parameters: load-cycle spectrum type and maximum load range. Correlations between the two parameters and the flight control data from various maneuvers are developed using flight load survey data. Pattern recognition method is used to identify (or correlate) the load-cycle spectrum type. Flight load models for the maximum load range are developed using multiple linear regression technique. Once the correlations are developed, only the flight control data are used by the fatigue processor to identify the load-cycle spectrum type, the corresponding component load range, and ultimately to compute the cumulative fatigue usage for the monitored components. Validation of the on-board fatigue processor was performed using flight load survey data and simulated flight conditions. The fatigue usages calculated by the fatigue processor compare well with the component fatigue usages computed directly from the measured component loads of the flight tests. Computation time for the fatigue usage calculation was done well below the processing time needed for real-time monitoring, on a small, personal computer platform. The method thus represents an efficient and practical monitoring approach for the on-board implementation in helicopters.