System Identification and Modal Extraction from Response Data

Aeroelastic stability or flutter testing is a critical part of the development of any new aircraft system, or configuration expansion. Each new aircraft and configuration needs to be assessed to ensure that it is free of any excessive and possibly destructive aeroelastic interactions. Such information could be determined from an appropriate model, but this information and insight is only as good as the model it was derived from. As such, there is a need to have a toolset that will identify necessary aeroelastic modal frequencies, damping ratios and mode shapes directly from flight test data and also compare this information against a known model. An additional complicating factor is that the driving excitation inputs to the aircraft are not always completely known, hence the identification techniques need to be capable of operating using only output sensor data. To meet these challenges, three identification methods that leverage both time and frequency domains are presented here and a variety of comparison metrics are presented to evaluate the relative accuracy of the identification approaches. Additionally, a real-time demonstration of many of these techniques was also conducted to validate the capabilities of the identification methods and comparison metrics.