Optimization of enhanced active constrained layer (EACL) treatment on helicopter flexbeams for aeromechanical stability augmentation

Abstract

This paper investigates the feasibility of employing enhanced active constrained layer (EACL) damping treatments on the flexbeams of soft in-plane bearingless main rotors (BMRs) for lag mode damping and aeromechanical stability augmentation. A finite element based mathematical model of the EACL damping treatment of the flexbeam has been developed and validated. A derivative controller based on the flexbeam tip transverse velocity is used in this investigation. A filter is implemented to remove the 1/rev component of velocity in the feedback signal. A thorough optimization/design study is conducted to understand the influence of various design parameters, such as viscoelastic layer thickness, PZT actuator thickness and edge element stiffness, on PZT actuator electrical field levels, induced axial stress levels and available lag damping. The results of this study show that the EACL treatment of the flexbeams has good potential for rotor stability augmentation.