Experimental and Analytical Study of Blade Lag Damping Augmentation using Chordwise Absorbers

Abstract

The feasibility of helicopter blade lag damping using embedded chordwise absorbers is investigated both analytically and experimentally. The basic feature of this approach is the use of tuned damped absorbers along the blades. This concept, utilizing a portion of the leading-edge weights that are already incorporated into the blade as a portion of the mass of the absorbers, can have the potential to replace or augment current blade lag dampers and reduce the complexity, aerodynamic drag, and weight of the rotor hub. The analysis is performed using an aeromechanical stability analysis program developed using the finite element method for the rotor system with blades incorporating absorbers. The test is conducted using a small-scale hingeless rotor with a single absorber on each blade. Parametric studies for blade lag damping augmentation with various absorber mass, location, damping, and tuned frequency are also presented. The analytical and experimental results show that blade damping augmentation using chordwise absorbers varies from 0.3 to 15% critical damping depending on the blade and the absorber parameters. The analytical results also show that the damping augmentation improves the ground-resonance stability of the rotor system.