Helicopter Noise Information for Airports and Communities (2016) / Chapter Skim
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Pages 27-34
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From page 27... ...
27 This appendix discusses two distinct matters: the nature of helicopter noise emissions (Section A1) and the relationship among various measures of helicopter noise levels (Section A2)
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28 the main rotor. However, the higher operating rpms of the tail rotor make the lower and mid-frequency tail rotor harmonic noise more noticeable and objectionable to a far-field observer.
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29 creates somewhat lower levels of harmonic noise, but at higher frequencies, and can be quite annoying. However, noise at these frequencies is reduced with distance from the source as a result of atmospheric absorption effects.
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30 Controlling BVI Noise in the Terminal Area As discussed previously, BVI impulsive noise occurs when the rotor operates near its own shed wake. Figure A4 shows that a vortex is shed from the tip of each rotor blade just as it does for a fixed-wing aircraft.
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31 FIGURE A6 Effect of operating condition on blade slap. FIGURE A7 BVI noise as a function of descent rate and level flight.
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32 a peak and then decrease with increasing rates of descent at approach air speeds. Because these pres sure pulses are very narrow they radiate most, but not all, of their energy in the mid- to high- frequency range and can easily annoy and disturb a far-field observer.
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FIGURE A9 S-76 noise abatement approach. FIGURE A10 Reduced ground noise with modified approach procedure.
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34 References for Appendix A1 Gervais, M
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