On the dynamic response of a hingeless helicopter rotor blade

Abstract

The intense nature of the aerodynamic environment surrounding a helicopter can cause excessive deflection of the rotor blades. Therefore, proper prediction of the aerodynamic loading and the blade deflection are necessary for monitoring the blade health. Compared to a rigid blade, the dynamics of a hingeless rotor blade is of particular interest for its inherent flexing tendency and strong coupling between different degrees-of-freedom of motion. With small-angle assumption, the deformed blade resembles a straight shape with constant flapping angle. However, in reality, the blade deforms with variable flapping angle with dynamic blade twist. In this paper, the coupled, steady-state dynamic response of the Bo 105 hingeless helicopter rotor blade is investigated at forward flight for different advance ratios without small-angle assumption. The velocity distributions are generalized and the torsional deformation is introduced to modify the total blade twist for deriving the corresponding angle of attack. The solution to the resulting nonlinear equations is obtained by formulating the generalized method of lines for coupled, flap-lag-torsion degrees-of-freedom in terms of time-varying deflections and other aerodynamic parameters. The deflections and other parameters obtained from this analysis differ significantly than that of the small-angle assumption. The model is validated by comparing the method of lines solutions with finite element and published results.