An Assessment of Current Methodology for Predicting Tiltrotor Blade-Vortex Interaction Aerodynamics

Rotor performance and airloads analyses have been applied to predict the aerodynamics of the XV-15 tiltrotor during landing approach flight conditions. The performance results are compared with flight data and reveal the importance of correctly predicting the vehicle trim in BVI calculations for tiltrotor configurations. In low speed descent, the highly twisted blades were also found to produce negative tip loadings which impact the rotor wake vorticity distributions and strongly influence the predicted tip vortex wake distortion. A full-span free wake code was employed to analyze the wake dynamics and BVI airloads in greater detail. This analysis employs a newly developed tip vortex rollup model which takes into account the low spanwise bound circulation gradients encountered near the blade tips on tiltrotors during low speed flight.