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Thread: 70cc twin exhaust

  1. #121
    Senior Member JDaly's Avatar
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    Re: 70cc twin exhaust

    Congrats Rick!

    So do you have access to a DB Meter to put some numbers where you say very quiet?
    Because everyone has their own opinion of what quiet is but Db’s don’t open it to interpretation!
    Windy You Ask? Well I have White Caps on my coffee, you be the Judge!

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    Re: 70cc twin exhaust

    Yes Jim, I have a DB meter. How do you want me to read it? How far away etc. I fly from a grass field and no way will this plane fit on a stand. Let me know how...

  3. #123
    Senior Member -Rick-'s Avatar
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    Re: 70cc twin exhaust

    101 bd about 7 feet away wide open throttle on grass.

  4. #124
    Senior Member JDaly's Avatar
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    Re: 70cc twin exhaust

    Quote Originally Posted by -Rick- View Post
    Yes Jim, I have a DB meter. How do you want me to read it? How far away etc. I fly from a grass field and no way will this plane fit on a stand. Let me know how...
    Quote Originally Posted by -Rick- View Post
    101 bd about 7 feet away wide open throttle on grass.
    Hi Rick,

    Sorry for not getting back to you before you were able to make test.


    At my club, the Oakville Milton Flying Club the standard there is 98db @ 3m. dB meter is 90 degrees to prop and meter is 12" off the ground.

  5. #125
    Senior Member -Rick-'s Avatar
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    Re: 70cc twin exhaust

    Quote Originally Posted by JDaly View Post
    Hi Rick,

    Sorry for not getting back to you before you were able to make test.


    At my club, the Oakville Milton Flying Club the standard there is 98db @ 3m. dB meter is 90 degrees to prop and meter is 12" off the ground.
    Okay I will do that when I get my new landing gear later this week. Had a dead stick 4 feet off the ground while dragging the plane in. Some how got crap in the carb.

  6. #126
    Senior Member -Rick-'s Avatar
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    Re: 70cc twin exhaust

    Jim, 93 db at WOT. 7300 rpm with a 24x10 wood.

  7. #127
    Senior Member rpm's Avatar
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    Re: 70cc twin exhaust

    Quote Originally Posted by -Rick- View Post
    Jim, 93 db at WOT. 7300 rpm with a 24x10 wood.
    Hey Rick, was that measured with the meter positioned as Jim described - @ 3m. dB meter is 90 degrees to prop and meter is 12" off the ground.

    I'm curious because I have some experience with sound testing at Humber Valley club and we did it at 25'. Knowing your meter position helps me compare. I forget what my DA70 measured at 25' but I'll look for it. I know it passed so less than 88 db at 25'.
    Humber Valley RC Flyers

  8. #128
    Senior Member -Rick-'s Avatar
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    Re: 70cc twin exhaust

    Quote Originally Posted by rpm View Post
    Hey Rick, was that measured with the meter positioned as Jim described - @ 3m. dB meter is 90 degrees to prop and meter is 12" off the ground.

    I'm curious because I have some experience with sound testing at Humber Valley club and we did it at 25'. Knowing your meter position helps me compare. I forget what my DA70 measured at 25' but I'll look for it. I know it passed so less than 88 db at 25'.
    I did by guessing at the distances of what Jim was asking for. Going out today and will take a tape measure with me. Three meters is just under ten feet so will try again. I will try it at twenty five feet as well. I don't know if I am getting some prop ripping as well, I do not know what prop ripping sound like. Never heard a plane ripping a prop. Will a wood 24x10 rip on the ground at 7300 rpm?

  9. #129
    Senior Member rpm's Avatar
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    Re: 70cc twin exhaust

    When we tested we did it 25’ off each wingtip and 25’ from behind and in front. I was surprised to learn the measurement from the front was always the loudest. The someone decided that was unsafe so I think now only the other 3 positions checked.

    I doubt your your prop will “rip” on the ground but really couldn’t say. I passed with a two blade but then sometimes flew s 3 blade and it was quieter.

  10. #130
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    Re: 70cc twin exhaust

    Okay. I will try in all four positions.

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