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Silencer for OS twins

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Old 03-24-2006, 04:00 AM
  #1  
mike@hibbins.org.uk
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Default Silencer for OS twins

Hi,
Does anyone know anything about silencing for OS twins. I have just acquired a OS Gemini 120 which I am going to build into a Great Planes Skybolt but I cant find anything about in cowl silencing!! Over here in the UK we need to get down to 82dB. I can turn, mill, weld etc so making myown won't be a problem if I can find any information.

Many Thanks

Mike
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Old 03-24-2006, 10:12 AM
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LesUyeda
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Default RE: Silencer for OS twins

Before going to any great pain, I would run the engine and see what it sounds like. I ran mine in a 1/4 scale Spacewalker with no silencers and you could not hear it idle at 25' away. Our club strongly enforced whatever our noise level requirements were, and no one even questioned mine. They are surprisingly quiet. The Magnum copy is much louder.

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Old 03-24-2006, 10:36 AM
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Default RE: Silencer for OS twins

It along with the Magnum 1.60 Twin are far quiter than a Gasser, and also appear to be quiter than most other 4 strokes. I would not say the Magnum is any louder. You are comparing a OS 120 twin to a Magnum 160 twin. I am willing to bet the magnum is no louder than an OS 160 twin. I installed a Magnum 160 in a friends cub and built a split cowl. I did all the break in and first flights, and that engine is just awesome. No on board glow with a 2,000 idle. The engine was no louder than his OS pegasus 4 cyl. It runs as the same if not better than the OS. The neat thing is, you can buy it for $450.00 or less.
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Old 03-24-2006, 10:45 AM
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Default RE: Silencer for OS twins

I hope you did not pay to much for 1.20 Twin, because they are not very powerfull. The OS 1.60 and the Magnum (exact copy) are far more powerfull for the same size and weight. I use to see a OS twin in a 1/4 scale Sig Cub, and it flew very scale like. It would not loop from level flight.
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Old 03-24-2006, 10:49 AM
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Default RE: Silencer for OS twins

There was an articles years ago on making your own silencers. The atricle showed how rifle caseing can be made into mufflers with simple brazing and silver soldering. There are countless sizes available. I caution that you must start with an empty case. nrver under any circumstance try to empy one.
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Old 03-24-2006, 12:02 PM
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Default RE: Silencer for OS twins

Whoa! [X(]

Make sure it is a primerless case as well!!!
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Old 03-27-2006, 10:37 AM
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Default RE: Silencer for OS twins

I've got a GP Skybolt also that I haven't started building yet, and I was thinking of the Gemini 120 as a potential powerplant. I haven't purchased anything yet. I'd love to learn more about your experiences - building (which from what I've read sounds pretty difficult) as well as powering it. The post saying how weak the Gemini 120 is doesn't sound promising, but so many guys overpower their planes these days that perhaps you'll be okay.

I'm sending this message privately as well as I don't reveal my email address in forums.
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