Comparison of First- and Second-Order EMA Models for an Aeroservoelastic Wing with Multiple Control Surfaces

Abstract

*An active flexible wing section with leading- and trailing-edge control surfaces is further investigated via the µ-method. Motivated by a more detailed servo control dynamics, the two electro-mechanical servoactuators (EMAs) K1 and K2, which command the deflections of the trailing-edge flap and the leading-edge flap respectively, are modeled as two secondorder shock absorbers in this study. The nominal and robust stability margins, modal properties, critical flutter airspeeds and frequencies are computed to predict the flutter of a nonlinear aeroelastic system and to investigate the aeroservoelastic stability in the µframework. The simulation results are compared with the previous study of which the controllers were modeled as the simplified (first-order) shock absorbers. The improved sensitivity to detect the control-structure coupling is observed by applying the second-order shock absorbers in the ASE model. Nomenclature h = plunge displacement α = pitch angle (angle of attack) β = trailing-edge flap deflection γ = leading-edge flap deflection V = freestream velocity ρ = air density a = nondimensional distance from the midchord to the elastic axis b = semichord of the wing cg r = distance from the elastic axis to the center of mass α x = nondimensional distance between the elastic axis and the center of mass p s = wing span h k = structural stiffness in plunge α k = structural stiffness in pitch with uncertainty nom k − α = nominal (linear) structural stiffness in pitch h c = structural damping coefficient in plunge due to viscous damping with uncertainty nom h c − = nominal structural damping coefficient in plunge due to viscous damping α c = structural damping coefficient in pitch due to viscous damping wing m = mass of the wing W m = total mass of the wing plus mount mass T m = total mass of the pitch-plunge system cam I = pitch cam moment of inertia wing cg I − = wing section moment of inertia about the center of gravity α I = total mass moment of inertia about the elastic axis