Validation of CHARM Wake Methodology for Computation of Loads and Vibrations

Validation of the CDI-developed CHARM advanced rotor wake methodology for rotorcraft was performed using Bell's comprehensive rotorcraft analysis code, COPTER, interfaced with the CHARM wake module. The analysis results were compared against flight test data to validate the CHARM free wake model. Several different four-bladed Bell helicopters, including M407, M427, and M429, were selected for the correlation and validation study. The predicted trim conditions, hub loads, and blade loads were compared against flight test data for the helicopter validation cases. The 4/rev components of the hub loads computed with the CHARM free wake correlated better with flight test data than those computed with COPTER's free wake model at high advance ratio flight regimes. The 4/rev hub moments significantly affect fuselage vibration and are important factors for helicopter design. The ability to predict more accurate vibratory hub loads is a major advantage of the CHARM free wake model over the existing COPTER free wake model.