Influence of Cross Section Variations on the Structural Behaviour of Composite Rotor Blades

Modern helicopter rotor blades with non-homogeneous cross sections made from non-isotropic material require a highly sophisticated structural analysis. Variations in cross section geometry make this task of analysis still more complicated. The analytical engineering theory of bending cannot describe all effects which are necessary. These effects are restraint warping due to cross section variations, restraint transverse deformations due to different Poisson’s ratios etc. With the finite element method (with three-dimensional solid elements) such influences can be described. However, the immense effort does not allow this method in general. Combinations of suited analytical methods with numerical FEM-based methods allow a cost effective and sufficiently accurate analysis of these complicated structures. It is shown that in general the one-dimensional engineering theory of bending combined with two-dimensional theories for determining the cross section properties is sufficient to describe the structural blade behaviour. Tests show a good coincidence with the theoretical results.