Evaluation of helicopter noise due to blade-vortex interaction for five tip configurations
Danny R. Hoad, United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch, Army Research and Technology Laboratories (U.S.). Structures Laboratory, Langley Research Center
National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1979 - Technology & Engineering - 77 pages
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51 knots 76 knots fig 82 knots A-weighted OASPL acoustic data amplitude and OASPL angle of attack AVRADCOM baseline blade passage blade-slap intensity blade-vortex interaction BVI blade slap Danny descent velocities effect of tip effective in reducing End plate end-plate tip Experimental Investigation Figure 11 flight conditions flight envelope flight-scaled free-stream velocity frequency Helicopter Acoustics Helicopter Blade-Slap Noise helicopter model Helicopter Rotor Hoad impulse peak amplitude impulsive noise Langley Research Center Langley V/STOL tunnel lateral-directivity characteristics low descent angles maximum peak amplitude measured by microphone Narrow-band analysis OASPL measurements ogee and subwing ogee tip One-third-octave-band analyses One-third-octave-band spectra Pressure time histories rotor model system rotor revolution rotor system simulated flight sound pressure level square tip square-tip subwing tip Swept tapered swept-tapered tip test chamber tip shape tip-shape tips installed tunnel velocity U.S. Army variation with descent various tips velocities of 51 vortex Wind Tunnel