Wind Tunnel Analysis of Helicopter Aerodynamics with Varying Rotor Head Blade Stub Lengths

Experimental investigations are performed on a helicopter wind tunnel model for three rotor heads with different blade stub lengths. This investigation is intended to judge the influence of the blade stub spanwise dimension on the drag, lift, and especially pitching moment characteristics. Aerodynamic forces, moments, and the wake flow fields are analyzed. As expected, the longest blade stubs provide the highest drag and lift coefficient along the angle of attack polar, while both shorter blade stubs show a similar force course. The flow field of the largest rotor head exhibits pronounced blade tip vortices, which influence the pitching moment polar at high angles of attack. The medium and long stubs show a similar flow field, while the hubcap vortex dominates the smallest blade stub configuration.