Investigation of Rotor Airloads and Structural Loads in Maneuvering Flight

Rotor airloads and structural loads encountered in the UTTAS pull-up maneuvering flight were investigated. Measured data from the NASA/Army UH-60A Airloads Program were compared with calculations obtained using the comprehensive analysis CAMRAD II. A nonlinear transient response was calculated in the time domain to the prescribed rotor pitch controls and aircraft motions. The semi-empirical ONERA EDLIN (Equations Differentielles Lineaires) dynamic stall model was used. A time step used in the transient response calculation was 0.001 second, which corresponds to approximately 1.53 deg azimuth angle. The calculated airloads and structural loads show reasonably good correlation with the measurements when the load factor is 1.0 or less. However, the analysis was not able to capture a significant increase in peak-to-peak magnitude as the load factor increases and the rotor experiences stall. The dynamic stall model, in general, has a small influence on the loads calculations.