Compact representation of multiple input/multiple output (MIMO) algorithms with applications to helicopter flight data

Analysis of correlated multiple input/multiple output systems are of paramount importance in problems concerning the system identification of physical systems like missiles, spacecraft, aircraft, rotorcraft, acoustics. To study the dynamic behaviour of such physical systems, it is important to investigate the spectral nature of correlated inputs/outputs and evaluate their separate and combined effects on any desired response of the vehicle. In this paper iterative algorithms for the solution of multiple input/multiple output problems formulated from flight test data are developed and presented in a simple form. A joint multiple coherence function is developed to study the combined effects of both states and controls. The algorithms are efficient to compute, analyse and interpret the results. Specific MIMO applications studied in this paper are the extraction of high quality frequency response functions and estimation of some lateral handling qualities of the BO-105 helicopter. A model structure for roll rate response to lateral cyclic stick representing dutch roll, coupled roll/rotor regressing flapping and lead lag/air resonance dynamics are presented in the transfer function model form. The time response simulation is also conducted to verify the accuracy of the extracted model. The results are compared with those available in the literature.