Nick Holmes 2 Posted January 3, 2009 Share Posted January 3, 2009 Hi, have an OS91 FS fitted to Showtime 90 4d, using a 14x7 APC prop too much noise creates 86db's over the 80db limited, fitted a 14 x 8 and the noise level reduced slightly to 84db's, has any one had experience as to how to reduce the noise to the 80 db requirement? Thanks Nick Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted January 3, 2009 Share Posted January 3, 2009 go electricAfter silencer? or lower max revs? Quote Link to comment Share on other sites More sharing options...
Graham King Posted January 3, 2009 Share Posted January 3, 2009 Mick Reeves quiet mount works well to reduce noise. And seating tape on the wing to fuselage join also helps. I used both of these on a noisy Mini Hype 3D with Western's superb but noisy West 36 engine. Got it down to 80Db from around 86. Quote Link to comment Share on other sites More sharing options...
Broken Prop Posted January 4, 2009 Share Posted January 4, 2009 OS do a silencer extension (well, it fits in the middle but you know what I mean ) for some of their engines. Not sure whether there is one available for the OS91 but the one for my 46LA worked brilliantly!Also, are the wheels a bit loose on the axles? If so, fitting soft nylon washers on each side will help to damp down the vibrations and consequent noise. Quote Link to comment Share on other sites More sharing options...
winchweight Posted January 4, 2009 Share Posted January 4, 2009 Bigger prop perhaps? IIRC my son had a 16" prop on his Funatana which had an OS91FS up front. It wasn't particularly noisy. Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted January 4, 2009 Share Posted January 4, 2009 Have just changed a 12 X 6 Master series K on my SC 91a 2 st for a 14 X 7 Graupner .Much quieter and I suspect enough power for my needs albeit it at higher airspeed although I've not flown it yet Too cold !I also have a couple of "extension" silencers made of the small gas lighter refill canisters modified with perforated ali tube 1/8 inch holes -about 20 through each end held with Araldite -( yes it holds ) with stainless steel scrubber washing up pad shoved loosely in between the canister and the tubing of course No baffles needed .I did try glass fibre originally but it gets all "gooed up "-don't see silicone tube advertised any more -Just expensive bent exhaust extensions for blowing goo onto one's underbelly., Not very scientific but VERY effective . You can treat 'er indoors to a pair of scrubbers & nick one -called killing two birds with one stone Biggest problem is getting hold of silicone tubing up here not scrubbers Quote Link to comment Share on other sites More sharing options...
Mike Hawkins Posted January 4, 2009 Share Posted January 4, 2009 Reading a mag article from a while ago, the hotter the exhaust the louder it is. The greater the surface area of the muffler the more heat is taken away. It depends on the space you have but from what I understand the expansion chamber as close to the engine as possible and a long tailpipe, or if restricted room, a smooth curved header pipe from engine to expansion chamber.Th article finishes with a suggestion to try Stainless Steel or Copper scouring pads in the canister (as Myron suggested) and the motto of the article is to expiriment and see what happens.The club I am in I think has a limit of 98dB, so in a way we are lucky, but we still try to be as quiet as possible because the land we use is virtually free due to a generous farmer. Quote Link to comment Share on other sites More sharing options...
Jimbo565 Posted January 9, 2009 Share Posted January 9, 2009 Just engines do a Super Quiet silencer for all 4st engines,pricey I think at around £40. Quote Link to comment Share on other sites More sharing options...
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