Noise characteristics of eight helicopters

PDFTech ReportFAA-RD-77-94HelicoptersAircraft noiseSound levelEffective sound pressureAcoustic emissionAcoustic measuring instrumentsRotor bladesAirspeedRotorsVirginiaUnited States. Federal Aviation AdministrationTrue, H.C.Rickley, E. J.United States. Federal Aviation AdministrationJohn A. Volpe National Transportation Systems Center (U.S.)AGR-IMPACTS-EnvironmentNTL-AVIATION-Aviation Energy and EnvironmentNTL-ENERGY AND ENVIRONMENT-Aviation Energy and EnvironmentVolpe National Transportation Systems Center, Technical Reference CenterThis report describes the noise characteristics of Eight Helicopters during level flyovers, simulated approaches, and hover. The data was obtained during an FAA/DOT Helicopter Noise Program to acquire a data base for possible helicopter noise regulatory action. The helicopter models tested were the Bell 47G, 206L, and 212 (UHIN), the Hughes 300C and 500C, the Sikorsky S-61 (SH-3B) and S-64 (CH-54B) and the Vertol CH-47C. The acoustic data is presented as Effective Perceived Noise Level, A-weighted sound pressure level and 1/3 octave band sound pressure level with a slow meter characteristic per FAR Part 36. Selected waveforms and narrow band spectra are also shown. Proposed methods to quantify impulsive noise ('blade slap') are evaluated for a level flyover for each of the Helicopters. The tested helicopters can be grouped into classes depending upon where the maximum noise occurs during a level flyover. Helicopters with the higher main rotor tip speeds propagate highly impulsive noise ahead of the helicopter. The maximum noise for most of the helicopters occurs near the overhead position and appears to originate from the tail rotor. Unmuffled reciprocating engine helicopters appear to have significant engine noise behind the helicopter. Noise levels, when compared as a function of gross weight and flown at airspeeds to minimize 'compressibility slap' form a band 7 EPNdB wide with a slope directly proportional to gross weight. The quieter helicopters have multibladed rotors and tipspeeds below 700 fps