Online Monitoring of Aircraft Modal Parameters during Flight Test based on permanent Output-only Modal Analysis

The process adopted for continuous monitoring of eigenfrequencies and damping ratios during the test flight of a research aircraft is presented. This comprises measurement hardware, distributed data acquisition system and software architecture in order to stream, store, and simultaneously analyze data with the methods of Operational Modal Analysis. The algorithms utilize only measured output time histories to identify modal parameters at different flight conditions. The autonomous implementations of the Stochastic Subspace Identification (SSI) and the Least-Square Complex Frequency domain (LSCF) algorithms provide estimations of the aeroelastic damping within a few seconds.