Whirl Testing of a Full-Scale Rotor with Flap-Bending/Twist Composite Coupled Blades

Whirl testing of a full-scale rotor with positive flap-bending/twist composite coupled blades was performed to evaluate the dynamic and performance effects of the coupling. A positive flap-bending/twist coupling, in which a flap up deformation induces a nose down elastic twist, was introduced in the blades through tailoring of the laminate layups; the magnitude of the coupling was maximized through an optimization of the layup, with the intent of maximizing the potential impact of the coupling for correlation purposes. An uncoupled version of the blade using the same geometry and materials was also fabricated to provide a baseline set of measurements for comparison, with the coupled blade optimized to also minimize changes in bending and axial stiffness properties in an effort to isolate the effect of coupling by itself. Rap testing was conducted to measure blade modal frequencies and shapes in a free-free environment. Whirl testing was performed for both the coupled and baseline rotors to measure frequencies and damping for stability, load distributions, and performance characteristics. Rotorcraft Comprehensive Analysis System (RCAS) models were run for all cases and are presented along with the measurements for correlation purposes; generally good agreement was observed in trends between measurements and predictions.