Virtual qualification of aircraft parts: test simulation or acceptable evidence?

The certification process of an aeronautical structural component is developed on a complex and articulated path. In particular, the certification regulations dictate requirements to be demonstrated to which certification of compliance is given by means of the evidence produced with specific qualification tests. This long and costly test activity lead, in some cases, to the sacrifice of test articles, interfering, if the results are unexpected, with the design process. In this scenario, the simulation of the test thus becomes a necessary prediction tool, which must be as accurate and predictive as possible. The test case reported here is a structure designed to equip a fleet of military helicopters with different observation devices. The qualification tests required by MIL-STD-810-G concerning durability and dynamic response were simulated. In order to increase the predictive power of the simulations, an intense experimental modal analysis campaign was carried out on which the numerical model was calibrated. The prototype of the structure was then subjected to an experimental flight activity, aimed at evaluating its functionality, and based on the data collected, to validate its numerical representation. The comparison between the simulated test and the exposure to the operating environment, have led to a critical re-reading of the standards, which involves all the test activity transversely, from the summary of the spectra to the the qualification tests compression. A case study based on the prediction of the qualification test that becomes the starting point for a critical analysis on the acceptability of the numerically produced evidences.