Correlation of Pitch‐Link Loads in Deep Stall on Bearingless Rotors

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Pitch‐link loads for bearingless rotors in deep stall are calculated using a unified state‐of‐the‐art methodology. The methodology includes a modern free wake model, advanced unsteady‐aerodynamic and dynamic‐stall models, and a rotor dynamics modeling for redundant load paths on bearingless rotors. Correlations of theory with measured pitch‐link loads are presented. The measured data are from wind tunnel tests of two 1/5 Mach‐scaled rotor models with the same bearingless hub but with blades having different torsional rigidities, and from flight tests of three full‐scale bearingless rotors with different torsional frequencies and solidities. Effects of blade‐vortex interaction, blade torsion stiffness, unsteady aerodynamics, and solidity on pitch‐link loads in deep stall are discussed. It is found that, for the range of torsional frequencies studied, the effcrt of blade torsion stiffness on the magnitudes of pitch‐link loads resulting from stall flutter is insignificant. Inclusion of a wake‐induced inflow model capable of producing a nose‐down impulse aerodynamic pitching moment resulting from retreating blade stall is sufficient to excite all harmonics and produce stall‐flutter characteristics.

Document Type: Research Article


Affiliations: Bell Helicopter Textron, Inc., Fort Worth, Tex.

Publication date: October 1, 1992

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  • The Journal of the American Helicopter Society is the world's only scientific journal dedicated to vertical flight technology. It is a peer-reviewed technical journal published quarterly by AHS International and presents innovative papers covering the state-of-the-art in all disciplines of rotorcraft design, research and development. (Please note that AHS members receive significant discounts on articles and subscriptions.)

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