Investigation of the UH-60A Slowed Rotor Wind Tunnel Tests using UMARC

Wind tunnel measurements of the performance, airloads and blade loads of the UH-60A Black Hawk rotor operating at 40% RPM and advance rations between 0.3 and 0.6 are compared to the comprehensive analysis UMARC, and its capability to predict the physics of the high advance ratio rotor is evaluated. The sensitivity of rotor thrust to collective is well predicted, but with an offset in collective. Attention is brought to the importance of modeling the drag in the root cut-out region to achieve good correlations to the rotor lift and power performance. The blade sectional normal force is well predicted in magnitude and phase, but for a region to the rear of the rotor disk. Pitching moments are poorly correlated. The important characteristics of the free wake model are assessed in terms of its impact on the sectional normal force. Flap bending moment peak-to-peak loads are underpredicted with some phase error. The high frequency 11/rev content in the torsional measurements is well captured by the analysis and shown to correspond to the excitation of the first torsional mode.