Potential hazards of wind turbine wake vortices for ultra-light sports rotorcraft

Abstract

Rotorcraft of the ultra-light class (autogiros and helicopters) operate from sport airfields, often with wind turbines (WT) in the surroundings. During their flight at typically low height above ground they may encounter the wake of the WT including the tip vortices. The wind deficit inside the WT wake tube is not large, but the much larger swirl velocities of the tip vortices spiraling around the wake tube may be of concern. The problem is two-fold: first, do pilots have enough control margin and/or authority to mitigate the vortex impact on their rotorcraft trim; second, in case of no pilot action: will the flapping developing be within allowed limits?