I'm interested in measuring the noise of helicopters. Does there exist some specific guideline?
Have you checked these:
http://www.faa.gov/regulations_policies/policy_guidance/envir_policy/media/04nov-30-rtc.pdf
http://www.flightsimaviation.com/data/FARS/part_36-appH2.html
The sound level meter is used to measure the helicopter by filter C. It is around > 100 dB
Thank you very much, do you have any idea how I can model the noise? Is possible to model them in INM and export the grid?
Yes, and you can post process the grid with NMPlot.
Or you can directly use FAA's HNM (Heliport Noise Model)
Basically, it depends on which version of INM you are using. From version 7.0 HNM is integrated with INM.
If you have a previous version, you can still use the standalone version of HNM 2.2 and then export the grid and post process it if needed.
The only problem is that HNM 2.2 is a DOS Program an have some (a lot of) issues if used in modern PCs. I wrote a paper for the AIAA/3AF Aircraft Noise and Emissions Reduction Symposium 2011 about this, if you need further explanations, feel free to ask.
Conference Paper Measurement and Characterization of Helicopter Noise in Stea...
A special acoustic flight test program was performed on the Bell 206B helicopter outfitted with an in-flight microphone boom/array attached to the helicopter while simultaneous acoustic measurements were made using a linear ground array of microphones arranged to be perpendicular to the flight path. Air and ground noise measurements were made in steady-state longitudinal and steady turning flight, and during selected dynamic maneuvers. Special instrumentation, including direct measurement of the helicopter's longitudinal tip-path-plane (TPP) angle, Differential Global Positioning System (DGPS) and Inertial Navigation Unit (INU) measurements, and a pursuit guidance display were used to measure important noise controlling parameters and to make the task of flying precise operating conditions and flight track easier for the pilot. Special care was also made to test only in very low winds. The resulting acoustic data is of relatively high quality and shows the value of carefully monitoring and controlling the helicopter's performance state. This paper has shown experimentally, that microphones close to the helicopter can be used to estimate the specific noise sources that radiate to the far field – if the microphones are positioned correctly relative to the noise source. Directivity patterns for steady, turning flight were also developed, for the first time, and connected to the turning performance of the helicopter. Some of the acoustic benefits of combining normally separated flight segments (i.e. an accelerated segment and a descending segment) were also demonstrated.
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