Assessing Community Annoyance of Helicopter Noise (2017) / Chapter Skim
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Pages 102-114
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From page 102... ...
102 This Appendix discusses two distinct matters: the nature of helicopter noise emissions (Section A.1) and the relationship among various measures of helicopter noise levels (Section A.2)
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Technical Discussion of Helicopter Noise 103 (Source: Old Army Report -- Circa 1974) Figure A-1.
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104 Assessing Community Annoyance of Helicopter Noise develops. The local transonic flow around the rotor blade often couples with this radiating acoustic field causing acoustic "delocalization" that radiates local shock waves to an observer in the farfield.
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From page 105... ...
Technical Discussion of Helicopter Noise 105 fundamentally the same as 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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From page 106... ...
106 Assessing Community Annoyance of Helicopter Noise present because the disturbance field of the wings induces periodic loading on the blades, creating far-field noise. A.1.2 Controlling BVI Noise in the Terminal Area As discussed above, BVI impulsive noise occurs when the rotor operates near its own shed wake.
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From page 107... ...
Technical Discussion of Helicopter Noise 107 Figure A-6 shows that this closeness can be controlled to some degree by the choice of the helicopter operating condition. In level flight, the helicopter's shed tip vortices pass under the rotor's tip-path plane and radiate small to moderate amounts of BVI noise.
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From page 108... ...
108 Assessing Community Annoyance of Helicopter Noise Source noise reductions depicted in Figures A-9 and A-10 are not always achievable in normal operations. Weather, winds, other flight traffic, and maneuvering flight can substantially change BVI noise levels.
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From page 109... ...
(Source: Schmitz, F
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110 Assessing Community Annoyance of Helicopter Noise Table A-1 lists the helicopters that are currently included in the INM database. Note that FAA has published a long list of substitutions for helicopters not included in the database and a recommended helicopter from the database to use as a surrogate for that helicopter.
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HELICOPTER INM NAME DESCRIPTION A109 Agusta A-109 B206L Bell 206L Long Ranger B212 Bell 212 Huey (UH-1N)
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From page 112... ...
112 Assessing Community Annoyance of Helicopter Noise Figure A-13 shows the 55 through 75 DNL contours for this generic helicopter test case. The grid points shown are 0.1 nautical miles apart (approximately 608 feet)
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From page 113... ...
Technical Discussion of Helicopter Noise 113 Figure A-14. Relationship of traditional level based noise metrics to DNL for an example heliport.
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From page 114... ...
114 Assessing Community Annoyance of Helicopter Noise Table A-2 shows the variance accounted for (coefficients of determination) for each of the noise metrics with DNL.
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