Active Aeroelastic Control Using the Receptance Method

Abstract

The control and manipulation of dynamic instabilities, such as flutter, is termed as aeroelastic control and is extremely important in designing next generation flexible and maneuverable aircrafts. One of the goals of an aeroelastic control is to extend stable fight conditions for a large range of aerodynamic flow conditions. The associated control problem deals in adjusting and assigning the eigenvalues (which determine the natural frequencies and damping ratios) of the aeroelastic system for achieving the desired closed-loop behavior by active or passive means. In this paper, an active aeroelastic control problem, associated with the wing model, is formulated and eigenvalue assignment to achieve flutter free flight envelope is developed by using a new control methodology known as the Receptance Method. This method is entirely based upon transfer functions, typically obtained from a standard modal test by using actuators and sensors. This method has several advantages over traditional aeroelastic control approach which leads to state-space formulations. For example, it does not require the estimation of structural matrices (i.e. mass, stiffness and damping) as well as rational function approximations of aeroelastic influence coefficient matrices. The control gains are obtained without the knowledge of system matrices and purely from the receptance matrices. The feasibility study of this approach for aeroelastic control is considered here using several simple numerical aeroelastic systems. The control gains for eigenvalue assignments are obtained from receptance matrices and the performance of the controller is compared with those obtained by the state-space approach. Numerical examples associated with the eigenvalue assignment problems to adjust the natural frequency as well as damping ratio and to extend the flutter envelope by active means are presented. The actuator dynamics of the control surface and its effect on receptance based control is also studied. We envision that this new approach will facilitate an alternative method to address aeroelastic control problems and eventually will provide a practical solution for implementing active aeroelastic control.