SIMULATION MODELING IN STEADY TURNING FLIGHT WITH REFINED AERODYNAMICS

The methodology to correctly couple a time- accurate free wake model to a flight dynamics sim- ulation was investigated. The simulation model is a coupled rotor-fuselage model with flexible blade modelling in flap, lag and torsion. Two free wake models capable of capturing correctly the wake ge- ometry distortions during maneuvering flight were used, a relaxation or iterative free wake model and a time-marching free wake model. The assumptions and limitations of these models make the first suit- able for steady flight conditions, while the second can model unsteady maneuvers. To be able to de- termine the transient response to of arbitrary am- plitude maneuvers with a time-accurate free wake model accurately, a two-phase trim process is nec- essary. This process consists of an initial trim with the relaxation free wake model and a conver- gence phase to obtain the equivalent geometry with the time-marching free wake, but free of numerical transients. The approach was investigated in low speed straight flight and steady turns. The results indicate that for hover and very low speeds the two models produce very similar geometries and almost identical induced velocities. For higher transition speeds and for turns at a high load factor, however, the dierences in the geometry between the relax-