Prediction of the fatigue lifetime of the Portuguese Air Force Epsilon TB-30 aircraft

Abstract

The operation performed by the Portuguese Air Force Epsilon TB-30 fleet is different from the one that was assumed as a reference operation. In order to establish a severity comparison between these two operation regimes and to predict the fatigue lifetime of the aircraft, the Portuguese Air Force developed an investigation that included the installation of two onboard systems.Firstly, the Modular Signal Recorder system was installed in 2017, comprising the installation of the MSR 165 equipment near the aircraft center of gravity which recorded load factor flight data that allowed the definition of the accumulated load spectrum for 1000 flight hours. Secondly, the Structural Health Monitoring system was installed in 2019, comprising the installation of an accelerometer near the aircraft center of gravity, strain sensors in the aircraft critical locations and a data acquisition unit (DAU). This system allowed the definition of transfer functions that correlate the load factor in the aircraft center of gravity with the stresses in the critical locations.Knowing the accumulated load spectrum for 1000 flight hours provided by manufacturer, the accumulated load spectrum for 1000 flight hours from the flight data analysis and the stress distribution in the critical locations, a crack propagation study and an accumulated damage calculation for both regimes were performed, allowing the severity comparison between them.These approaches led to the conclusion that the Portuguese Air Force Epsilon TB-30 fleet has been performing a more severe operation than the one that was considered as a reference by the manufacturer. According to this study, the difference may vary between 2% and 20% which can contribute to a reduction of the aircraft fatigue lifetime defined by the manufacturer.