UH-60A Rotor Structural Loads Analysis with Fixed-System Structural Dynamics Modeling

NASA/Army UH-60A Airloads Program flight test and full-scale UH-60A Airloads wind tunnel test data are investigated in order to better understand and predict the chord bending moments, one of the unresolved issues in the UH-60A rotor loads prediction. Effects of the lag damper model are examined with the coupled Helios/RCAS by calculating lag damper loads using a nonlinear lag damper model or by applyingmeasured lag damper loads as prescribed external loads. RCAS alone analysis is also performed by prescribing measured airloads from the tests to help identify whether sources of inaccuracies in the structural loads prediction originate from deficiencies in aerodynamics or structural dynamics. Both lag damper loads and airloads are important for the accurate prediction of chord bending moments. The effects of drivetrain dynamics on the chord bending moment for the flight test and the effects of hub impedance using test stand NASTRAN model on the chord bending moment for the wind tunnel test are also investigated. In general, the effects of drivetrain dynamics are small. There is a slight improvement for the 4/rev and 5/rev harmonic magnitude correlation. The effects of hub impedance improve the correlation of both 3/rev and 4/rev harmonic components.