Loads and Stability Analysis of an Unmanned Tilt Rotor

Abstract : Loads and stability calculations for a proposed unmanned tilt rotor aircraft are presented. Blade loads are calculated using the comprehensive analysis CAMRAD II and the multibody dynamics analysis DYMORE II for helicopter, airplane, transition, and maneuvering flight. Gust loadings are investigated for some of the maneuvers. Good agreement of bending loads is seen between the two analyses, particularly in airplane mode. Torsion moments differ substantially between the two analyses with the smallest difference in airplane mode. Rotor-wing stability is examined using DYMORE II. A parametric study of wing beam mode damping with varying rotor and wing properties for semi-span and full-span models is presented. No instabilities are observed for the parameters examined. Beam mode damping is found to be particularly sensitive to blade precone angle, wing torsion stiffness, and pylon conversion actuator stiffness. Reduced fuselage roll inertia due to fuel burn is found to increase beam mode damping. Correlations of isolated rotor lag frequencies and damping ratios between the two analyses also compare favorably.

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