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I Hear A Huey Popping!

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I was at work one Saturday faithfully doing my job, but in the back of my mind was helis or Huey. I knew I that I heard one coming but it certainly was taking a long time. I started my stopwatch and waited and waited. The Huey grow louder and louder and literally 8 minutes past before it was finally flying overhead. It appeared as though it was flying nearly 100-110 knots. Of all Helis, Why are Hueys and Cobras SO LOUD. (by the way I and I'm sure you love them when they are LOUD)

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There is all sorts of theorys why medium blade sound sounds the way they do, none of which I can remember at the moment. What amazes me is the distance the sound travels. A few winters back I was at Cambridge Bay waiting for my machine to return when I started thinking about this blade noise thing. As soon as I could hear the very faint noise of the machine (Bell 212) I called the Pilot and asked him how far out he was. To my utter shock, he replyed 30 miles!! Mind you, the temp. that day was -25 and he had a very brisk tailwind so I'm sure that had a lot to do with how far the the sound travelled, but just the same--30 miles!!. Jeez.

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Found this. Seems AR is on the right track.




Defense Technical Information Center

Accession Number : ADA043842


Title : Noise Characteristics of Eight Helicopters


Descriptive Note : Final rept.




Personal Author(s) : True, H. C. ; Rickley, E. J.


Report Date : JUL 1977


Pagination or Media Count : 170


Abstract : 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.




Subject Categories : ACOUSTICS


Distribution Statement : APPROVED FOR PUBLIC RELEASE





Search DTIC's Public STINET for similiar documents.


Members of the public may purchase hardcopy documents from the National Technical Information Service.

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Just love the sound of the mighty mediums. Occassionally they are on fires here with a 212 or 205 and you can easily hear them taking off and coming back and forth to the airport 15+miles away.


Nothing like the sound of helicopter noise and the smell of Jet fuel in the morning! :lol:



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