The report presents technical information and procedures for estimating the noise levels produced by current civil and military helicopters (piston- and turbine-powered) during varied flight and ground operations. Information and procedures are also presented for comparing helicopter noise with other vehicle noise, and with ambient noise found in typical urban and suburban areas. These procedures permit an assessment of the extent to which helicopter noise is compatible with typical land uses (residential, commercial, industrial, etc.) in areas near heliports. Noise data and procedures are presented in simplified fashion. The information may be readily used by those without specialized acoustical training but who are concerned with the location and development of a heliport, or with land planning or land zoning in the vicinity of heliports. (Author).

This 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.

The potential noise problems anticipated with future VTOL aircraft are analyzed and discussed in general terms, and a brief review of the basic principles of noise generation of various types of propulsion systems proposed for VTOL is included. Primary consideration is given to the noise environments produced in areas adjacent to VTOL sites, since they could cause the most serious noise problem limiting the usefulness of VTOL aircraft. Contours of perceived noise levels are compared for different takeoff and landing profiles of 3-4 passenger, 60 passenger, and 25 ton-lift-crane VTOL aircraft. Criteria and methods for assessing the response of communities to noise from V-port operations are discussed along with the problem of detection of military VTOL aircraft by means of noise. Recommendations are given on the requirements for future research on these noise problems with emphasis on the need for considering noise as an integral part of the design, selection, and test of VTOL aircraft.