| Abstract | The research reported in this paper examines both established and new system identification techniques for rotorcraft flight-model renovation. Flight behavior models based on legacy aircraft are often the starting point for a new design and the fidelity, or model accuracy, can be validated when data are gathered in early flight testing of the new prototype. As data flow in, so flight models can be improved in fidelity, eventually supporting certification, provided the correct physics are embodied. System identification has become an established method for enhancing fidelity and suggesting causal relationships between flight and flight-model mismatches and missing physics. The objectives of our investigation include extending current system identification methods to address nonlinear model structures, and establishing appropriate approximations to the complex rotorcraft aeromechanics required to enhance fidelity, including maneuver wake distortion effects. The research is focused on renovation using Liverpool’s FLIGHTLAB Bell 412 simulation model based on data gathered on the National Research Council’s Advanced Systems Research Aircraft. We build on earlier work using frequency-domain methods, ideally suited to linear model structures and flight conditions sufficiently stable to allow control sweep data to be gathered. For hover and low-speed flight, strong nonlinearities caused by rotor-wake effects and significant deviations from the trim conditions, require a different approach and the paper shows how a new time-domain approach enables model structures and the parameters to be identified incrementally. |
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