High-Fidelity Modelling of Actuation Systems for Nonlinear Aeroservoelastic Analysis of Tiltrotor

Recent evolutions in regulatory practices place an increasing emphasis on nonlinear aeroservoelastic analysis to prevent adverse phenomena like Limit Cycle Oscillations (LCO). Thanks to enhanced computational capabilities, this field is set to take an even more important role in the certification process of new aircraft, and in particular of tiltrotor, together exploiting the increasing ability to build multidisciplinary and high-fidelity modelling of complex aeronautical systems. In this paper, a comprehensive model of a tiltrotor control surface actuation system is introduced, capable of accurately representing the main nonlinear features and helping to better comprehend their origin. The model includes the entire control chain, starting from the Flight Control System (FCS) logic and getting to the control surface structure, passing through the hydraulic servo-actuator and the related mechanical linkages. The behavior of the servo-actuator model as a subsystem and the one of the entire control chain are compared to experimental data. Finally, a simplified nonlinear aeroservoelastic simulation shows the potential effects of the nonlinearities present in the system.