Airworthiness Tests of the UAV Structure − Fatigue Issues

The paper presents investigations undertaken in order to support developing the UAV airworthiness requirements, in particular those concerning fatigue aspects. Knowledge about UAVs load spectra is of vital importance for fatigue issues. The results of preliminary research are presented in this paper. A description of the load spectrum processing is given, starting from filtering the input-data, and then either counting the load signal transfers or implementing the Rainflow Counting algorithm and presenting the results in the form of a transfer array or halfcycles array. This description is illustrated by three examples of flight tests of 4-meter class UAVs, designed at Warsaw University of Technology. They concern flights controlled in a manual and automatic way in order to show differences between the LSs for such control modes. Besides the LS processing, a method for statistical analysis of load spectra from several flights is also presented to address the important problem of LS dispersion. Finally, there are shown selected tests of the UAV structure elements for which load spectra may have a crucial importance