Flutter margin augmentation synthesis using normalized coprime factors approach

Abstract

This research is concerned with the design of a flutter margin augmentation system at a supercritical flutter condition subject to control capacity constraints. The control law is synthesized using the //oo loop-shaping method at the normalized coprime factors framework, and order reduction processes are applied to both the nominal plant and the synthesized controller. The effects of output weighting on the control capacity and the influence of the controller suboptimality over its reduction process are further investigated. Robust stability analyses dealing with unstructured uncertainties and sensitivity studies by variation of the fundamental flutter parameters are presented. In transonic wind-tunnel tests, the resulting fourth-order digital controller extends the closed-loop flutter dynamic pressure of an aeroservoelastic wing model by 11.4% over its open-loop value, despite discrepancies in the analytically predicted flutter parameters. Nomenclature B = process noise distribution matrix g = gravity acceleration K®S(s) = gain from output disturbance to controller output K®SG(s) = gain from input disturbance to controller output S(s) = gain from output disturbance to plant output SG(s) = gain from input disturbance to plant output W = intensity matrix r] = zero-mean Gaussian white-noise process