Investigation of Tip-Vortex Modifications on Rotor Loads and Performance

This paper studies the influence of tip vortex modification on the airloads and performance of the helicopter for high speed steady level flight and unsteady maneuver using a lifting-line based comprehensive analysis. The tip vortex modification is modeled inside the free wake model of the comprehensive analysis in three different ways: (1) the location of tip vortex release point is altered, keeping the strength constant, (2) strength of the tip vortex is diminished by certain factor while keeping the release location constant, and (3) both the release location and strength of the vortex are altered simultaneously. The modification of tip vortex release location is observed to have significant influence on rotor power during both steady and unsteady flight conditions analyzed. Moving the tip vortex outboard of blade tip by 5%, 10%, 15% and 20% of chord in the simulation resulted in power reduction ranging from 11.5%-18.5%, 20%-32.5%, 28%-46% and 35%-59% respectively for the unsteady pull-up maneuver.