A Simple Method to assess the Aeroservoelastic Stability through Open-Loop Frequency Response

This work presents a simple method of assessing the aeroservoelastic stability characteristic of an aircraft through the open-loop frequency response function. The method is based in well-known classical control theory concepts, as well as already defined aeroelastic response techniques. It uses classical tools of both control systems and aeroelasticity disciplines. The model is separated in two parts: the aeroelastic airplane and the control system. The frequency response of each part is obtained separately, taking advantages of the tools most suitable to each discipline. Then, they are multiplied to obtain the complete openloop frequency response necessary to analyse the stability characteristics of the closed-loop system. By separating the responses, the focus is to obtain an efficient solution with less effort and cost, a necessity of an industrial environment. The advantages and disadvantages of the open-loop approach in comparison to the classical closed-loop eigenvalues solution approach (flutter solution) are discussed through examples.