Aeroelastic Stability of the LCTR2 Civil Tiltrotor
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MOFFETT FIELD CA AMES RESEARCH CENTER
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A new generation of very large tiltrotors is being studied to meet emerging transportation requirements. With gross weights well in excess of 100,000 lb, such aircraft will require new technologies for acceptable weight. Wings and rotors will have different per-rev frequencies and mode shapes than current tiltrotors, so coupling between destabilizing aeroelastic modes may differ from past experience. This paper presents aeroelastic stability analyses for a Large Civil Tiltrotor LCTR2, with emphasis on combined rotorairframe stability whirl flutter in cruise. LCTR2 design features include low cruise tip speed of 400 ftsec, a four-bladed hingeless rotor, and a structurally tapered composite wing. The effects on whirl-mode stability of wing and rotor structural properties mass and stiffness, control-system stiffness, solidity, precone, and cruise tip speed were examined using CAMRAD II. Common nonlinear trends of damping were seen for several structural parameters for both the rotor and wing.