Accurate prediction of rotor blade structural loads is a difficult and important capability required of comprehensive rotorcraft analyses used for helicopter design. Recently, improved structural load predictions have been obtained by using computational fluid dynamics (CFD) airload solutions coupled with computational structural dynamics (CSD) solutions, but the high computational cost associated with this approach precludes its use for daily design work. This paper describes recent work incorporating Continuum Dynamics Inc.'s CHARM fast lifting surface blade model, full-span free-vortex wake model and panel fuselage model as modeling options within the U.S. Army's Rotorcraft Comprehensive Analysis System (RCAS) and evaluating the use of some of these new modeling options in the prediction of rotor structural loads. Loose- and tight-coupled procedures analogous to those used in CSD-CFD coupling were developed and found to be generally robust and computationally efficient. Structural load and pushrod load predictions with the RCAS-CHARM coupled analysis were compared with test data for five rotor systems at low and high speed. Several blade/wake modeling options are compared. Structural load and pushrod load predictions obtained with the new coupled analysis are accurate enough to be of value in daily rotorcraft design work.
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