Frequency identification of helicopter for flight control design

A frequency identification method of helicopter for flight control design is presented. The overall concept is to extract a complete set of non-parametric input-to-output frequency responses that fully characterizes the coupled helicopter dynamics, partial coherence analysis is used to eliminate the inter-axis coupling, and conduct a nonlinear search for a transfer function model that matches the frequency-response data set. Each major element of the procedure is reviewed. A new method for combining the results of multi-input frequency-response analyses obtained from a range of spectral windows into a single optimized response is presented. This method significantly improves the dynamic range and accuracy of the identified frequency-response relative to single window methods. The accuracy of the identified model is verified by comparing the model-predicted responses with the responses collected during flight experiments.