A Study of the Aerodynamics of a Helicopter Rotor Blade

Abstract

In any congested area, where a fixed-wing aircraft cannot perform, rotary-wing counterparts are the best-suited option for its vertical take-off and landing capacity. The vibration induced by the rotor blade is a significant problem in helicopter performances. Rotor aerodynamic loading, rotor dynamics, and fuselage dynamics are the elements that contribute to the vibration of a helicopter. Among these elements, the key reason for the helicopter vibration is the aerodynamic loading. Determining aerodynamic loading is one of the most important criteria to design a rotor blade and to minimize vibration. Rotor harmonic airloads are generated from the rapid variation of flow around the rotor blade due to the vortex wake. A rapid drop in the circulation near the blade tip causes tip vortices which are the reason for the maximum lift at the tip of the blade. Consequently, tip vortices become the primary source of harmonic airloads. In this study, a specimen of Bo 105 helicopter rotor blade is considered to observe the aerodynamic characteristics under the external flow of air. The coefficients of lift and drag of the specimen for different angles of attack and azimuth angles are estimated. The resonance frequencies and the mode shapes are obtained. Computational results are validated by the experimental analyses of a small-scaled model of the rotor blade. From the study, the coefficient of lift is found to increase with the angle of attack up to a critical value. Similarly, the coefficient of drag increases with the angle of attack. The resonance frequencies significantly change with scaling the rotor blade.