Evaluation of Helicopter Noise Due to Blade-vortex Interaction for Five Tip ConfigurationsNational Aeronautics and Space Administration, Scientific and Technical Information Branch, 1979 - Acoustical engineering - 77 pages |
Common terms and phrases
12.5 One-third-octave-band center 51 knots 76 knots fig 82 knots A-weighted OASPL acoustic data amplitude and OASPL angle of attack blade passage blade-slap intensity variation Blade-tip shape blade-vortex interaction BVI blade slap dBA Ppeak descent velocities dynes/cm Effect of tip End plate 50.4 end-plate tip Figure 11 flight conditions flight envelope Flight-scaled OASPL free-stream velocity helicopter model Helicopter Rotor indicate knots O Square Langley Research Center lateral-directivity characteristics low descent angles maximum peak amplitude measured by microphone Narrow-band analysis NASA ogee and subwing ogee tip One-third-octave-band analyses One-third-octave-band center frequency One-third-octave-band spectra polyurethane Pressure time histories rotor revolution rotor system shape on blade-slap shape V knots shape Voo Sound pressure level square tip square-tip subwing tip Swept tapered 50.6 Swept tapered End swept-tapered tip tapered End plate tip shape tip-shape U.S. Army variation with descent velocities of 51 vortex Wind Tunnel