Performance and Loads of a Lift Offset Rotor, Part II: Prediction Validations with Measurements

The predictions of an upgraded UMARC comprehensive analysis are compared to experimental lift offset rotor results. The experiments cover a range of collective pitch angles (theta degrees) from 2 degrees to 10 degrees, advance ratios (mu) from 0.21 to 0.53, and lift offset from 0% to 20%. The experimental model rotors are from a system of coaxial hingeless rotors, with two blades each, and a first flap frequency of approximately 1.6/rev. The simulation is compared with isolated rotor performance and controls with lift offset, loads, and pitch link forces. Increasing efficiency with increasing lift offset, the impact of lift offset on different loads, and the dependence of pitch link loads on pitch bearing damping are identified in the experiment and correlated with the simulation.