Fatigue Load Spectra for a Conventional Military Rotorcraft

This paper extends the author's prior effort to provide a framework for fair, early, and meaningful assessment of rotorcraft fatigue durability. In this paper a comprehensive set of fatigue load spectra have been characterized for a conventional military rotorcraft and provided for potential future use by the reader. The author's method of mixed-Weibull parameterization has been improved over the prior method. Mixed-Weibull parameterization allows grouping of various sets of load paths as well as analytical comparison of the distributions. This paper includes an assessment of sensitivity to changes in airspeed limitations at altitude, as well as an assessment of sensitivity to human influence during mixed-Weibull parameterization. Once standardized mission spectra are established, they will prove useful in fatigue life specification verification, preliminary and detailed design, and structural test planning.