System Identification and Modal Extraction from Response Data

ABSTRACT: Aeroelastic stability or flutter testing has been and will continue to be a critical part of the development of any new aircraft system or configuration expansion to ensure that it is free of any excessive and possibly destructive aeroelastic interactions. In Phase I, novel identification techniques were combined into a toolset capable of performing real-time identification of aeroelastic modal frequencies, damping ratios and mode shapes directly from output-only flight test data, and present these data in a clear manner via prototype displays. In addition to validation with flight test data, real-time simulations were performed using an aeroelastic high speed fighter aircraft model and a live pilot to demonstrate the capabilities. Phase II will build on these successes by iterating upon and improving the accuracy, efficiency and robustness of each of these identification algorithms and displays. Comprehensive validation will be performed with abundant flight test data and live piloted simulations and will address poor sensor readings, loss of telemetry and other failures. The result of Phase II will be a validated toolset: Modal Identification Software Toolbox (MIST), an IADS-based control room tool used to identify aircraft modal frequencies, damping ratios and mode shapes in real-time using live telemetry data. BENEFIT: The benefits of the resulting MIST software are twofold: increased confidence in the safety of the aircraft and reduced flight test costs. By better informing the control room of the status of the aircraft, in particular its proximity to a potential flutter region (determined by examining the modal damping values), a more informed assessment of the state of the aircraft can be made. With this knowledge, potentially dangerous flutter regions can be avoided and known stable regions more confidently established, increasing flight safety for the pilot. In addition, decisions to expand the test envelope can be made in flight rather than requiring extensive evaluations post flight before the next round of testing. This ability to test more points more confidently in one flight can also reduce costs by minimizing the required flight test time dedicated to these evaluations and the additional costs associated with supporting the control room and staff.