Effcient Implementation and H∞ On-Blade Control Design of the EC-145 Rotor for Vibration Reduction

This thesis presents the development and implementation of a comprehensive helicopter active rotor model, and the design of robust control laws operating on a wide region of the cruise flight envelope for reduction of vibration originated by the main rotor. The vibration mitigation methods are tested on a hingeless analytical rotor model of the four-blade Airbus EC-145 helicopter demonstrator, with the main rotor blades mounted with active trailing-edge flaps. The model was implemented in MATLAB and Simulink and has been validated against the more comprehensive model CAMRAD II (Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics) and flight test data. The integrals of blade-element aerodynamic forces were solved analytically and implemented in closed-form for improved accuracy and computational efficiency. The design of a single set of control algorithms can provide vibration reduction for hover, 20, 40, 60, 80 and 100 knots forward flight. The ability to obtain a single set of control laws offer the benefits of reduced processing power and relaxation of implementation requirements in practical scenarios while guaranteeing very good performance levels. To enable the application of H1 control design methods, system identification tools are applied to extract Linear-Time-Invariant models at the considered flight conditions. Two types of vibration reduction approaches are considered: i) The first approach takes into account the 4=rev vertical force component only, which is the dominant component in the vibration signature. ii) The second approach, being more general, considers all six force and moment vibration component at the rotor hub. The first approach provided around 47.05% vibration reduction on average, while the second improves the average vibration level to 68.07%. We discuss in the thesis benefits and drawbacks of each approach in terms of robustness properties, performance and implementation requirements.