On the twist performance of a multiple-cell active helicopter blade

This paper discusses how torsional stiffness is related with twist actuation in an integrally twist actuated rotor blade. It shows that increase in torsional stiffness does not necessarily reduce the twist actuation. Improvements in twist actuation for a realistic airfoil-shaped beam can be achieved while controlling the blade torsional stiffness within aeroelastic requirements. These design trends can be studied once an appropriate anisotropic beam analytical formulation with integral anisotropic piezoelectric actuators is developed. The new analytical model revises and extends the closed form solution for thin-walled multi-cell beams based on the variational-asymptotical method and introduces the distributed anisotropic piezoelectric actuator effects along the cross section of the blade. The model is applied to specifically investigate the relationship between twist actuation performance and torsional stiffness of a realistic active blade. In this study, both analytical expressions and numerical examples are examined. The results show that the torsional stiffness can be increased by up to 20% with an increase in twist actuation of approximately 5% from their corresponding baseline values. Moreover, the results also indicate that a single-cell model is insufficient to address qualitatively and quantitatively the complex interaction that exists among the wall members of a two-cell airfoil cross section.