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  1. #1

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    Noise control for big gassers.

    Hi,
    Some guys here in Ireland are trying to get IMAC up and running.
    Normally there are no noise limits in IMAC - as I understand it !!.
    However here we are bound by our National rules where there is a noise limit of 96db at 3m.
    Also for F3M there is a 96 db limit over tarmac and 94db over grass - both also at 3m - so this must be possible !!?

    I am looking for guidance on what will get 50cc to 80cc singles and 80cc to 210cc multiple's under these limits.

    Mounts ,props, exhaust silencers etc.

    All help appreciated but especially examples of actual installs c/w results.

    Brian

  2. #2
    speedracerntrixie's Avatar
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    Brian, while we don't send anyone home for loud airplanes we do have a " sound score ". I assume that eventually we will have to adopt some sort of noise restrictions but this is America the home of Nascar, Monster trucks, Supercross and Country Western music. We like our noise!

    All kidding aside there are ways to get them quiet. The biggest gains are simply the construction of the airplane and the prop. An all moulded airplane will resonate less noise then a typical all built up film covered airplane. Most airplanes are quite over powered so while running a 3 blade prop will reduce overall performance slightly it will also reduce the amount of prop nose which is where most of the noise comes from. Select a prop that will keep the RPMs down below 6800 rpm for a single and 5500 rpm for a large twin. You will of course need to run a canister exhaust system. Using some sort of soft mounting system for the exhaust will help too. Being that all our gassers use industrial carbs finding a suitable filter should be fairly easy. You would be surprised how much noise comes back through the carb. I have never used a soft mount on a gasser myself so I am not able to say if they work well or not. IMO I would leave that as a last resort. I know that Merle Hyde will make mounts here in the US for big gassers and Also Toni Clark in the UK may have something.

  3. #3
    MTK's Avatar
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    Brian,

    Look at my Derivative thread in regular Pattern, Originally the model was set-up on a piped and soft mounted DLE55. It turned a Mej 20x12 3 blader and had terrific manners and sound. Didn't measure it actually but I would guess noise to be around 95dB at 3 meters. That's pretty quiet as gassies go but it also on the bottom of your displacement spec

    The fuse was all composite with balsa sheeted foam wing/stab and that may have been a contributor to some noise. All balsa fuse with appropriate soft mount such as that shown in those photos would deaden noise even more. I'd stay away from built up wings and stabs with plastic coverings. I make soft mounts for all my gassies but have not made anything for an engine larger than 60cc. Good luck and if you need more specifics, contact me directly at my email....
    Regards,
    MattK
    (Rcmaster199@aol.com)

  4. #4

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    Hi Matt,
    Thank you - I will direct the guy's there.
    I am just helping them in general / trying to get good guidance for them.

    To that end any and all examples of specific installs and results attained would be appreciated.

    I was in F3A/pattern when the rles came into force for turnaround.
    Then, for a while, some guys insisted on dealing with it using props, build methods and silencers.
    These all helped but engine mounts, soft isolating types, proved to be the real answer.
    I think it is fair to say that there is not a single soft mounted engine in an IMAC model in Ireland at this time.
    We need to reinvent the wheel - again !!

    Brian

  5. #5
    MTK's Avatar
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    Quote Originally Posted by serious power View Post
    Hi Matt,
    Thank you - I will direct the guy's there.
    I am just helping them in general / trying to get good guidance for them.

    To that end any and all examples of specific installs and results attained would be appreciated.

    I was in F3A/pattern when the rles came into force for turnaround.
    Then, for a while, some guys insisted on dealing with it using props, build methods and silencers.
    These all helped but engine mounts, soft isolating types, proved to be the real answer.
    I think it is fair to say that there is not a single soft mounted engine in an IMAC model in Ireland at this time.
    We need to reinvent the wheel - again !!

    Brian
    Yes, true enuff! I think most F3A'rs have forgotten more than the rest of the aerobatics pilots out there have never learned. Until I actually went ahead and did mine, I didn't expect it would have been possible to do with off the shelf components. That is, to have a 40 sized glow engine on its regular muffler actually drown out a 55cc gassie.

    The whole package that has worked so well is as follows:

    DA return to center flex header, flex section treated with my flex ceramic fix. The teflon tape (original) just doesn't last well
    ES Composites 55G gas pipe, set to 29" to baffle, following the exhaust path. It is also soft mounted by a single lord mount. And BTW, there are no straps or other paraphernalia holding the pipe. The lightest and most secure way to mount the pipe to the soft mount takes a bit of prep but is worth it. I apply some carbon directly onto the pipe and securing nut. the Lord mount screws into the nut and is then secured to the fuse. Simple....
    Coupler, my own ceramic flex. Only needs plastic tie wraps top hold
    Mezjlik 20x12 3 blader carbon hollow prop
    My own soft mount, which, BTW, only weighs about 3 1/2 ounces

    Long time followers of my scribble may remember these developments.

    Brian, BTW, I have a new-old innovation regarding wing, stab, rudder builds that may be interesting to you. I will discuss it on the Classic Pattern Forum. Those guys are still building their crates and benefiit the most from these innovations/techniques.
    Regards,
    MattK
    (Rcmaster199@aol.com)

  6. #6

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    Matt,
    Look forward to that.

    Brian


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