In the arcane world of helicopter rotor aerodynamics, two concepts that show promise for enhancing safety and performance in the world of high-density-altitude heavy lift are under development on opposite sides of the U.S. Briefings on both were presented at the American Helicopter Society’s annual forum last month in Phoenix.
Dr. Preston Martin of the Army/NASA Rotorcraft Division at Ames Research Center of Mountain View, Calif., described one concept– a variable-droop leading edge (VDLE) device that has been tested in the Ames wind tunnel. The other, a miniature trailing-edge (MiTE) “effector” (trim tab) for active rotor control, was conceived and mathematically modeled by faculty and students at Penn State University’s aerospace engineering department. It has been tested in the PSU low-speed wind tunnel.
The VDLE concept was studied as part of an Army-sponsored research program to explore dynamic rotor blade stall onset and control. Previous work had shown a dynamically deforming leading-edge airfoil and a slatted rotor blade airfoil to delay stall onset, but both had limitations. The VDLE airfoil, drooped dynamically on the retreating side of the rotor disc, proved to offer a way to modify local adverse flow effects and improve airfoil performance on the retreating side. Test results indicated slight reduction in maximum lift, a large reduction in maximum drag, and significant reduction in peak pitching moment. Martin noted that the hinged model VDLE tested in the Ames wind tunnel is a concept demonstrator and that “application of this concept to a rotor blade requires a completely different design.”
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