FLUTTER DETECTION USING WAVELET-BASED TIME-VARYING TRANSFER FUNCTIONS

The use of an Automatic Flutter-suppression System (AFS) increases the challenge of flutter flight-testing because the aircraft is required to fly in a region where it is open loop unstable. Paradoxically, the presence of the AFS can be exploited to anticipate the onset of wing flutter. The phase margin of the AFS control loops and the closed loop damping of critical modes are critical parameters that can be monitored. In this paper, we develop Wavelet transform based tools to analyze flutter flight test data to monitor the stability of the system. Flutter margin definitions are reviewed and new definitions for use when an AFS is present are proposed. Then, a so-called TimeVarying Transfer Function (TVTF) is defined in terms of wavelet transforms of the input and output signals. Finally, the analysis of flutter with TVTFs is illustrated in two examples, using simulated flutter test data.