Identification of the Flutter Boundary During Flight Testing Using Operational Modal Analysis

Flutter is a complex phenomenon resulting from the coupling between aerodynamics and structural dynamics. The consequences of this dynamic instability are usually catastrophic failure of the aircraft. With increased efforts in numerical simulation and improved accuracy of simulation models, future aircraft concepts might be designed to operate even closer to the stability boundary. Furthermore, active control technology like flutter suppression might be required for safe operation. To demonstrate the identification of the flutter boundary during flight tests, an unmanned flutter demonstrator was designed and built in the EU FLIPASED project. The wings were designed to flutter with a bending torsion coupling. An online monitoring system was developed to identify and track the flutter critical modes using Operational Modal Analysis (OMA) in real-time. The OMA system was able to robustly identify and track the flutter critical modes. The aeroelastic damping of the symmetric wing torsion mode was tracked from 3.3% to 0.4% indicating that the aircraft was on the edge of the stable flight envelope. The outlook of this flutter monitoring system is envisioned to provide further safety in flutter flight testing.