Aeroelastic Response with Non Linear Hydraulic Servo-Actuator Model

The present paper is focused on techniques aimed at including a hydraulic servo-actuator model into the aero-elastic equation system. The test case is the elevator actuator of an EASA CS-25 business jet. The first step has been the servo-actuator dynamics modeling. A co mparison between linear models (Taylo r series and harmonic balance based) and the fully nonlinear model has been done in order to verify the linear approach. Differential equations governing the servo dynamics models are man ipulated in order to obtain full 2nd order equation systems, by adding a "fictitious term". This technique allowing fo r mass matrix inversion during aero-elastic response calculation has been chosen because it does not alter the servo dynamics behavior. The last step has been the inclusion of linear and nonlinear servo-actuator models in the aero-elastic system. The co mparison between the linearized and nonlinear formulat ions is made in terms of aero-elastic behaviour and flutter speed.