Real-Time Estimation of Bare-Airframe Frequency Responses from Closed-Loop Data and Multisine Inputs

Abstract

A method is presented for estimating frequency responses of multiple-input multiple-output bare-airframe dynamics from flight test data containing feedback control and/or mixing of control effectors. Orthogonal phase-optimized multisines are used to simultaneously excite each input with unique harmonic frequencies, at which frequency responses are computed as ratios of output-to-input Fourier transform data. The confounding effects of feedback and mixing are resolved by interpolation of the frequency responses. The analysis can be run in batch for postflight analysis, or in real time as the aircraft is flying. The effectiveness of the method was verified using simulations of the subscale T-2 generic transport airplane with rate feedback. The method was also demonstrated using flight test data from the X-56A MUTT aeroelastic airplane, which was flown with both feedback control and mixing.