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O.S 91 FS Muffler Question

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Old 04-29-2007, 05:46 AM
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cathurga
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Default O.S 91 FS Muffler Question

Hi All,

I had asked a similar question a few months ago and have not really received a conclusive answer (I know you are all smarter than me, so I am hoping one of you has the key :-0)

I want to remove the muffler from my OS91FS, I am not in the least concerned about any noise problem, but I obviously need to have a pressure line to the tank. I was considering fashioning an extension to the header and routing it to some semi-scale positions on the plane, and then just tapping in a valve to attache the pressure line. Given the shape of the muffler, I am convinced that the design helps to up the pressure to sufficiently pressure in the tank....am I reading this right?

On the topic, is the engine a lot louder with no muffler? I have not tried it, but I am not convinced it is going to be toomuch louder..

Thanks all for any input you can offer..\regards
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Old 04-29-2007, 07:25 AM
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w8ye
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Default RE: O.S 91 FS Muffler Question

The engine is not much louder without a muffler.

Yes, you will need a slight restriction in your pipe's outlet to create pressure for your tank.
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Old 04-29-2007, 08:12 AM
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Flyboy Dave
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Default RE: O.S 91 FS Muffler Question

I lost the back half of the muffler on my Magnum 1.20 a couple years back. The
engine was so loud it caused pain in the ears. I fly out in the desert where there
is no noise restriction what-so-ever....I had to put the plane away and fly something
else....I didn't have any hearing protection, and trying to tune the engine was too hard
on the ears. Of course when the muffler lost the back half it threw the tuning of the
engine off because of the loss of fuel tank pressure and the back prssure to the engine
it had with the muffler in proper operating shape.

FBD.
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Old 04-29-2007, 11:10 AM
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w8ye
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Default RE: O.S 91 FS Muffler Question

When you loose the back half of a muffler, what you have left is a "Megaphone". It amplifies the sound of the engine. This does make the engine noticeably louder.

I have several Saito engines with no muffler. Just a straight pipe. They do not sound any louder than the engines with mufflers.
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Old 04-29-2007, 12:39 PM
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blw
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Default RE: O.S 91 FS Muffler Question

I've seen an OS Surpass run a straight pipe and it didn't sound any louder.
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Old 04-29-2007, 04:42 PM
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Harry Lagman
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Default RE: O.S 91 FS Muffler Question

I run my OS .91 Surpass without a muffler. It's still quieter than a muffled OS 1.20 Surpass. When flying at less than full throttle, I struggle to hear my unmuffled .91's engine at all if someone is flying a standard .46 two-stroke at the same time.

One of our club members has a scale model with an unpumped OS .91 Surpass, fitted with a straight pipe. He does not run tank pressure at all, instead hanging the tank vent line overboard. It runs fine without tank pressure.
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Old 05-06-2007, 03:06 PM
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Default RE: O.S 91 FS Muffler Question

Thanks for all the answers guys.

Harry? When you say he is flying a scale airplane and does not use the tank pressure, thne how has he connected the tank? Inlet to carb from clunk, filler pipe into tank and then the pipe normally used for t pressure is hung out? I am assuming here that at it is a scale plane, he is not doing stunts, so he doesn't need the constant delivery of a stunt flyer?

I have put a header on mine, with the flex-pipe running down through the fuse, to where the scale exhaust come out (corsair warbird) I have drilled and tapped a nipple into the header, and as I am not flying stunts, I might be able to get away with it. I am not sure whether the fuel tuping will survive being on that nipple, got a feeling it is going to burn off, think the temp might be a bit high there....whaddya all think?
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