EFFECT OF ROOT CUTOUT ON HOVER PERFORMANCE.
Final rept. Jun 69-Apr 70,
UNITED AIRCRAFT CORP STRATFORD CONN SIKORSKY AIRCRAFT DIV
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Tests were conducted to determine the effect of blade root cutout on the hovering performance of a helicopter rotor. Rotor thrust and torque characteristics were measured on model rotors with root cutouts of 10, 25, 40, and 50 percent radius. In addition, smoke was ejected from various spanwise locations along the trailing edge of blades with cutouts of 10 and 50 percent. The wake patterns developed below the hovering rotor were photographed and examined for several rotor speedcollective pitch combinations to determine how these parameters affect the wake structure. The test data revealed a loss in hovering efficiency of 5 to 7 percent for the 50 percent cutout rotor at a typical design thrust coefficient. This result is in agreement with previous calculations made using blade element-momentum theory. The loss in hovering efficiency was highly nonlinear with increasing root cutout. This behavior was not predicted by blade element-momentum theory or a prescribed wake hover performance analysis using a standard wake pattern. The flow visualization phase of the investigation showed that the increase in root cutout decreases the radial contraction of the tip vortex. When this result was included in the prescribed wake analysis, the correlation accuracy was improved. Author