Investigation of Load Collectives on Transport Aircraft Using Continuous Turbulence for Fatigue Analysis Purposes

Abstract

This paper elaborates a numerical method to derive load spectra of aircraft wings due to continuous turbulence. This method can serve as a part of an aircraft fatigue analysis in early design stages. For that aim, reference flight missions including the payload and fuel masses are defined. For each flight phase, stress transfer functions of the observed positions on the wing are derived, and a normalized von Karman turbulence spectrum is generated. Subsequently, stress responses resulting from the transfer functions and the turbulence spectra are calculated, and the occurrence distributions are derived using a rainflow-counting algorithm. Furthermore, probability distributions of turbulence intensities are generated to obtain the expected load spectra of the observed positions in one flight. These can be extrapolated to represent e.g. an aircraft's service life of 40000 flights. This method is demonstrated using a mid-range aircraft configuration and compared with the TWIST (Transport Wing Standard Load programme) spectrum, which is commonly taken as reference in fatigue analysis in aircraft pre-design. Moreover, several parameter variations are conducted to investigate the sensitivities of the proposed method.