I have a newly built float plane which I installed an OS 91 FS motor. I fly the plane at my lake and I am a little bit concerned about the noise it makes when flying - I don't want the neighbours to get annoyed.

Is there any other muffler/silencer solutions for 4 stroke engines that can make them run more quietly? If so how might I get one and will they sacrifice engine performance?

I have a Seamaster which has an OS 46 FX and I put a super silencer exhaust on it which makes it a lot quieter.

I know this is not exactly a seaplane related question, but I would suspect that others flying on water would have had this issue as well.

Thanks.

WOW it must be really quiet where you fly. OS 91FS engines are pretty quiet.

I found a noticeable difference in perceived noise when I switched to an APC prop. Also, a 3-blade of slightly smaller diameter would be quieter because of lower tip speeds.

I have see guys who ran a rubber tube from the exhaust to keep the slime off the plane..but that would damp out the exhaust noise, too.

Thanks.
Yes you are right - it is very quiet where I fly.

The lake is in Northern Montana and is small and there are no power boats allowed on it. Perfect for swimming, canoeing and fishing.
Due to the location of my cabin and the sun in the day, the best time for me to fly is in the evening or at dinner time - just when everyone else is sitting on their deck eating. So its not like I get drowned out by boats or jet skis - I'm the only one making noise!

I'm just trying to make sure that I do not cause undo attention or annoyance.

I would have thought OS would have made a silencer, seeing as they've done if for the 2 strokes.

As Jim said 3 blade prop and prop brand will make a big difference...you can also try and run as much pitch as you can... on your 91FS a 13x10 would probably be about as much as it will turn without hurting over all performance. You could also try one of these http://www.davisdieseldevelopment.co...er/4stroke.htm problem here is the size... their not exactly small... they really don't reduce over all DB that much BUT the tone is more pleasing to the ear so it seems quieter... kinda like comparing a Saito 91 to an O.S.91... the Saito is probably just as loud... is just doesn't have the same tone/roar the O.S has given the same prop RPM range.


John

As others have said, look for a quiet prop. This needs to be emphasized; the prop makes at least as much noise as the exhaust. And the noise from both goes up exponentially with RPM. If you use an APC prop in a size that will keep your full throttle rpm down to 9000 or so, you will be amazed at the difference.

Jim

Noise is directly proportional to how much you lean on the throttle. Throttling back once airborne makes a big difference in the noise footprint. Next you can load the engine with a larger prop. The 4 strokes dont mind lugging a bit (doesn't work to well if you are doing aerobatics, but it you are just shooting circuits or flying around, it will help ease the noise). An after muffler will help...some 4 strokes have quite a bark to them which can be annoying to non-flyers. You are pretty much on your own here, but I have seen guys use that Aerotrend blue silicone pipe and strap on a lawnmower muffler behind the stock muffler. Another idea is to take an ordinary 2 stroke muffler, turn the baffle around and used that same silicone pipe to join the outlet of your 4 stroke to the outlet of the 2 stroke muffler. The exhaust travels backwards through the 2 stroke muffler and exits out of what normally be the manifold end. Beauty with this is that it can be mounted on the belly and the "outlet" rotated to point straight down....which keeps tthe gunk off your model... Dubro use to market the ARISE muffler (DUB707), but it has been discontinued, but still may be found in some hobby shops...it was a bolt on quiet muffler for 4 strokes.

One other tip...make sure that everything is tight on the model so there are no rattles, and balance the prop to minimize airframe vibration...if the model is ultra- or mono-cote covered, it can act like a drum if there is any resonance......

rossdre
I have a 1/4 scale Cub with the same engine, 14-6 APC prop, small lake, lots of people. My situation isn't as severe as yours but the FS exhaust is still too loud for my liking. A super muffler is on my wish list too. In the meantime, I never fly in the morning for obvious reasons and rarely in the evening when there is no power boat activity to mask the exhaust sound. If there's no wind and the air is damp, the noise footprint is much larger than usual. In that scenario, I'll take off at minimal power, fly over the bush and climb to a high altitude. Over water flying is at a high idle until it's time to climb out over the forest again. When it's time to land I like to kill the engine with the airplane as high as I dare. The glide takes a couple of minutes and the last thing my neighbours see... and remember...is a silent Piper Cub splashing down in front of my dock. Interestingly, the only time I've ever had a complaint about my floatplanes was while flying a 48" span electric with an Astro 035. An elderly neighbour said I was scaring the loons. Meanwhile her 3 stupid Boxers are barking their heads off all day long on the end of her dock!