TIP VORTEX CORE THICKENING FOR APPLICATION TO HELICOPTER ROTOR NOISE REDUCTION
BOEING CO MORTON PA VERTOL DIV
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Helicopter rotor noise levels are sharply increased when a rotor blade intercepts the rolled-up tip vortex trailed by a previous blade. The study deals with modification of the induced velocity structure of the vortex from both an analytical and an experimental standpoint. Ten tip configurations were evaluated in a wind tunnel, to determine the magnitude of velocity reduction achievable. Results indicated that the maximum velocities induced within the vortex core could be reduced to about 12 percent of those for a standard tip formed by revolving the tip airfoil section about the chord-line and typical for many present generation helicopters. Drag data measured on the model wing for each blade tip indicates that most configurations adversely affect performance.