Stability analysis for a nonlinear model of a hydraulic servomechanism in a servoelastic framework

The effects of mounting structure stiffness on mechano-hydraulic servomechanisms actuating aircraft primary flight controls are modeled by a six-dimensional nonlinear system of ordinary differential equations. Stability analysis of equilibria reveals the presence of a critical case that is handled through the use of the Lyapunov–Malkin theorem. Stability charts are drawn using the Routh–Hurwitz criterion for the stability of a fifth-degree polynomial. Comparison with previous results shows how the stability of equilibria can be ensured exploiting the positive influence of structural feedback.