Analytic extraction of the elastic coupling mechanisms in composite blades

Abstract

An aeroelastic model for a hingeless helicopter blade with a composite flex-beam is presented. The model employs structural analysis for laminated flex-beams of solid cross-sections with symmetric layup, and the study encompasses configurations with Beamwise Bending-Twist coupling and Chordwise Bending-Twist coupling. The structural dynamics of blades with coupled composite flex-beams is studied by a special purpose methodology that allows the creation of a refined uncoupled reference blade for each case. This procedure enables the determination of the net effects which are induced by the elastic couplings. By examining the stability characteristics of the blades in the frequency domain and their response in the time domain, the paper supplies additional information regarding the trade-off between stability and vibration characteristics in both the transient and the steady-state, forward-flight regimes. The analysis also examines the effect of different types of composite materials and quantitatively identifies the relation between elastic properties and their potential to improve blade stability margins.