Frequency-Response Method for Rotorcraft System Identification: Flight Applications to BO 105 Coupled Rotor/Fuselage Dynamics
Authors: Tischler, Mark B.; Cauffman, Mavis G.
Source: Journal of the American Helicopter Society, Volume 37, Number 3, 1 July 1992 , pp. 3-17(15)
Publisher: AHS International
Abstract:A comprehensive frequency-response method for rotorcraft system identification is presented. The overall concept is to 1) extract a complete set of non-parametric input-to-output frequency responses that fully characterizes the coupled helicopter dynamics, and 2) conduct a nonlinear search for a state-space 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 eliminates the need for manual optimization of windows and significantly improves the dynamic range and accuracy of the identified frequency-responses relative to single window methods. An integrated user-oriented software package for the frequency-response method is described: Comprehensive Identification from FrEquency Responses (CIFER). CIFER is used to identify a 9-DOF hybrid model of the DLR BO 105 dynamics from flight test data at 80 knots. The identified model includes coupled body/rotor-flapping and lead-lag dynamics, and is accurate to 30 rad/sec. The 9-DOF results are compared with 6-DOF (quasi-steady) identification results. An application of the model to flight control design shows that the maximum roll rale gain is limited by the destabilization of the lead-lag dynamics.
Document Type: Research article
Publication date: 1992-07-01
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