Lichten Runner-up Paper: Hingeless Rotor Aeroelastic Stability Measurement and Validation at High Advance Ratios

Abstract:
A 5.5-ft diameter dynamically-scaled hingeless rotor was tested at high advance ratios (μ) up to 1.4, representing the first aeroelastic stability characterization of a hingeless rotor at high-μ. This paper describes the wind tunnel test setup, hover and forward flight stability data, and comprehensive analysis predictions. A novel rotating frame piezoelectric actuator-based perturbation system located in-line with the pitch links is developed to excite the blade pitch. Damping is identified via the matrix pencil method, which is shown to outperform the moving block method for the highly damped flap mode. Hover data shows constant flap damping until stall onset, where a drop in damping is observed and captured by the University of Maryland Advanced Rotorcraft Code (UMARC). UMARC has been modified to solve for elastic blade stability using linearized perturbation equations in conjunction with Floquet transition matrix theory. Elastic blade modeling is shown to be required for accurate high-μ stability predictions. In forward flight, three rotor speeds are tested corresponding to three different flap frequencies and comprehensive analysis predictions are compared against wind tunnel data. Scatter in extracted damping values is addressed using Kernel Density Estimation (KDE) to robustly identify the mode of the extracted damping distribution across repeated trials. This work validates the capability of a novel perturbation and damping extraction system to experimentally characterize rotor aeroelastic stability at high advance ratios.

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