Assessment of comprehensive analysis predictions of helicopter rotor blade loads in forward flight

Comparisons of helicopter rotor blade loads, between rotorcraft comprehensive analysis predictions using a free vortex wake model and measured data, are provided for the UH-60A, SA 330 (research Puma), SA 349/2, and H-34 rotors in forward flight. The rotors are modeled as being isolated from the rest of the vehicle. The comparisons encompass a total of 24 test points featuring wide variations in advance ratio for a thorough assessment of the predictions. With the exception of chord bending moment for the case of UH-60A, the analysis correctly predicts trends in half peak-to-peak values of blade structural loads and pitch link force. Most of the predictions in half peak-to-peak blade structural loads and pitch link force deviate from the measured data by no more than 40% and most of the deviations are underpredictions. The predictions typically resemble the measured data in shapes of the waveforms for both flap bending moment and normal force, but this is less often the case for chord bending and torsion moments. While the analysis may capture the 1/rev harmonic contents in pitching moment waveforms, it consistently underpredicts any higher harmonics.