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OS 91 FS Surpass II Noise problem

Best way to reduce engine noise on OS91FSII

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Nick Holmes 203/01/2009 17:42:00
26 forum posts
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
Tim Mackey03/01/2009 19:09:00
20920 forum posts
304 photos
15 articles

go electric

After silencer?  or lower  max revs? 

Graham King03/01/2009 22:10:00
98 forum posts
20 photos
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.
Broken Prop04/01/2009 13:36:00
624 forum posts
1 photos

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.

winchweight04/01/2009 16:19:00
2516 forum posts
67 photos
Bigger prop perhaps? IIRC my son had a 16" prop on his Funatana which had an OS91FS up front. It wasn't particularly noisy.
Myron Beaumont04/01/2009 18:07:00
5797 forum posts
51 photos

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

Mike Hawkins04/01/2009 23:52:00
60 forum posts
1 photos

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. 

Jim Carss09/01/2009 10:20:00
2103 forum posts
77 photos
Just engines do a Super Quiet silencer for all 4st engines,pricey I think at around £40. 

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