Aerodynamic design optimization of helicopter rotor blades including airfoil shape for forward flight

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This study proposes a process to obtain an optimal helicopter rotor blade shape including both planform and airfoil shape for helicopter aerodynamic performance in forward flight. An advanced geometry representation algorithm which uses the Class Function/Shape Function Transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape was considered in terms of design variables. The optimization process was constructed by integrating several programs developed by the author. Airfoil characteristics are automatically generated by an analysis tool where lift, drag, and moment coefficients of airfoil are predicted for subsonic to transonic flow and a wide range of attack angles. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight, aerodynamic requirements (lift, drag and moment coefficients) for critical flow condition occurring on rotor blades. The trim condition must be attainable in any flight condition. Objective function is chosen as a combination expression of non-dimensional required power in hover and forward flight.