Geometric Scaling Effects of Bend-twist Coupling in Rotor Blades

Blade lengths of 30, 50, 70 and 90m were designed to quantify the effect of geometric scaling on bend-twist coupling. The blades were implemented with off-axis carbon fibers in the spar flanges to promote coupling while biaxial glass fibers were used to provide torsional stiffness and buckling resistance. Theoretical scaling laws were compared to nonlinear finite element simulations, both of which concluded that there was no dependence of bend- twist coupling on geometric up-scaling. At the maximum load, all blades achieved a tip twist between 6 and 7° towards feather. This resulted in load reductions of roughly 10-11%, showing that load alleviation from bend-twist coupling was also independent of scaling effects. The reduction in loads showed potential for blade mass reduction.