International audienceThe achievements presented in this communication propose a model based approach to propagate the Flight Control System requirements to the actuation system with the aim to identify each subsystem contribution and then think a global optimization of the actuation system architecture and sizing. Within the helicopter’s Flight Control System, many functions are encapsulated, making the global performance dependent of each subsystem. Hydraulic power generation and distribution impact the actuators performances, which dynamics are influencing the global helicopter control loop performances. After presenting some recommendations in terms of pipes and actuators sizing, the new global modeling approach is introduced. The actuation system model is described with its interfaces, including degrees of freedom on its architecture, and its key parameters. Open loop simulations – based on real flight data – and closed loop simulation – responses to commands needed for maneuvers – are detailed with their respective advantages. The contribution of this global modeling approach to the final design is presented and perspectives are given