On the modeling of integrally actuated helicopter blades

This paper presents an asymptotical formulation for preliminary design of m ulti-cell composite helicopter rotor blades with integral anisotropic activ e plies. It represents the first attempt in the literature to asymptoticall y analyze such active structure. The analysis is broken down in two parts: a linear two-dimensional analysis over the cross-section, and a geometrical ly non-linear (beam) analysis along the blade span. The cross-sectional ana lysis revises and extends a closed form solution for thin-walled, multi-cel l beams based on the variational-asymptotical method, accounting for the pr esence of active fiber composites distributed along the cross-section of th e blade. The formulation provides expressions for the asymptotically correc t cross-sectional stiffness constants in closed form, facilitating design-t rend studies. These stiffness constants are then used in a beam finite elem ent discretization of the blade reference line. This is an extension of the exact intrinsic equations for the one-dimensional analysis of rotating bea ms considering small strains and finite rotations, and now taking account o f the presence of distributed actuators. Subject to external loads, active ply induced strains, and specific boundary conditions, the one-dimensional (beam) problem can be solved for displacements, rotations, and strains of t he reference line. Analytical and numerical studies are presented to compar e the proposed theory against the previously established analytical models. Discrepancies are found for general blade cross-section and discussed here in in details, especially for the piezoelectric actuation components. Direc t results of the present formulation are also compared with experimental da ta. (C) 2001 Elsevier Science Ltd. All rights reserved.