Comparison of laboratory testing techniques for airborne store's dynamic response to in-flight environmental conditions

The paper presents a study of the vibrations that develop on inner components of a weapon system in captive flight, and their replication via mechanical vibration and acoustic tests. The goal of the study was to examine which testing method is more suitable for predicting flight loads, to examine different excitation methods, and to define the drawbacks and limitations of each testing approach. This should eventually lead to a testing methodology (or a combination of analyses and tests) that should lead to a good prediction of in-flight loads with reduction in the number of flight tests, and avoiding structural components redesign. For this, mechanical vibration tests and acoustic tests were conducted on a weapon system, using various excitation methods, and the resulting component loads were compared to those measured in captive flight. It was found that mechanical vibration tests are suitable for generating the load power spectral densities (PSD) in the low frequency range with good correlation to flight test data. However, due to the boundary conditions in the test, and the single-axis excitation approach, mechanical vibration tests cannot accurately reproduce flight-related vibrations in all three directions. The acoustic test did less good in exciting the low frequencies, but provided a good excitation, in all three directions, in the mid frequency range, up to 3kHz. The control approach in the acoustic test could not perfectly mimic the flight acoustic PSD throughout the whole frequency range. It thus remains as future work to study and test other control approaches. The study provides a basis for future acoustic tests that will aim at predicting component loads as measured in captive flight, possibly together with acoustic simulations.