Robust aeroservoelastic stability margin analysis using the structured singular value

A new framework based on structured singular value (μ) analysis is introduced to evaluate the robust stability margin of an SISO aeroservoelastic system with the structural and actuator uncertainties considered. The essential of the proposed method is to extend the nominal gain margin concept based on open-loop analysis to robust stability margin by introducing an extra uncertainty. This newly developed stability margin framework is performed on a large aspect ratio wing model with GVT data to evaluate the considered uncertainties. Three main results are obtained from the current work: (1) The measurement of robust stability margin, compatible with the classical nominal margin evaluation, is practical to associate the nominal aeroservoelastic system and the perturbed one. (2)The results show that the aircraft may go critically unstable with only 0.9% frequency variations, though gain margin of the nominal aeroservoelastic system exceeds 6dB. (3) The sensitivity of gain margin is defined and calculated numerically to decide the most important uncertainties affecting the stability margin. The result shows that the damping ratio of the elastic structure can be omitted to save computation time of μ because of its relative small sensitivity.