Full Vehicle Simulations of a Helicopter in Steady Autorotation

In this paper a full vehicle UH-60A helicopter with and without stub wings is simulated in steady autorotation using both the flight dynamics (FD) code HeliUM-A and the computational fluid dynamics/computational structural dynamics (CFD/CSD) solver CREATE-AVTM Helios. Significant effort was put into trimming the CFD/CSD simulations to an autorotative state that is representative to how the aircraft flies in practice, and the method for doing so is described. For the baseline aircraft, both FD and CFD/CSD predictions of the vehicle's autorotational descent rate were in excellent agreement with available flight test data. CFD/CSD analysis showed that the presence of the fuselage led to a significant positive pitching moment on the rotor as well as a sudden loss of loading as the rotor blades pass through the fuselage wake. When External Stores Support System (ESSS) stub wings were added to the model, both solvers show both quantitative and qualitative agreement in their predictions of the increase in autorotational descent rate due to the additional ESSS drag. CFD/CSD analysis showed that the stub wings had minimal effect on the interactional aerodynamics between the airframe and rotor.