Mailing List Message #65325
From: Finn Lassen <>
Subject: Re: [FlyRotary] Re: Exhaust setups
Date: Mon, 11 Nov 2019 14:33:16 -0500
To: Rotary motors in aircraft <>
No, it's simply a 2.5" tube welded onto the outlet of the Hushpower "muffler".

If I remember correctly, the innards of the Hushpower muffler were all blown out when I did this. But the key to noise reduction in the cockpit seems to be to get the exhaust pointed away from the cockpit. Granted, probably doesn't do much for people on or near the airport :)

Yes, it may increase drag to have the plume(s) pointed down instead of aft. I didn't try to measure that.


On 11/11/2019 12:40 PM, Matt Boiteau wrote:
It's behind the rear bulkhead by a ft or so. The perforated store bought sheet is extremely holey, found in typical mufflers. I do have a 4ft 2.5" solid tube I bought just incase i drill my own holes.

Is your exhaust tube inside a surrounding tube? Or you just extended the current exhaust (2.5" or 3"?) 3 ft more, capped off the end of it?

- Matt Boiteau

On Mon, Nov 11, 2019, 11:20 Finn Lassen <> wrote:
On?? my RV-3B I added a 3' long pipe with 1/8" holes drilled in the bottom of it (faced down). Tube closed at the end. Area of the 1/8" holes add up to the cross section are of the tube.
That did reduce the noise in the cockpit noticeably.

Is your final exit well behind the cockpit? If so, the sound must be transmitted through the surrounding (outer) pipe.


On 11/11/2019 10:29 AM, Matt Boiteau wrote:
Yes more or less like the coax muffler. Instead of drilling a few holes here and there, I bought a perforated sheet and welded it into a tube. I wanted to have it open on both ends, to create a vacuum and help suck the air out of the cowl. But right now to make flights enjoyable, I might close up the ends and see how that works.

Is anyone running a coax muffler ? Because it's extremely loud in my case.

I did buy the??Aero Exhaust AT2525XL and it worked great while doing all my ground testing, but the 6" outer shell was just to big to fit under the plane. Sadly I brought it back home to Canada and haven't flown with it yet here in FL. I'll pack it in my suitcase next trip down.

The racing beat presilencer is suppose to be good. I believe it has stainless steel wool inside and maybe ceramic mat over that. For fun I stuffed ceramic mat into the 4" pipe and it did quite things down. Except with the 4" tube being open at both ends, it sucked it out. Right now I'm trying to source some high temp ss fiber mat to first wrap the pipe, then wrap the ceramic over that, then close up both ends.

1.5minutes into the take off the EGT probe right before the 4" pipe is 1700F. ?? (EGT1 = 1768F, EGT2= 1819F)

- Matt Boiteau

On 2019-11-11 5:19:37 AM, Le Roux Breytenbach <> wrote:

Matt: So the setup for your exhaust, is more or less the one that Paul
Lamar suggest in his forum, 2 years or so ago.?
The coax muffler ?
Le Roux Breytenbach

On Mon, Nov 11, 2019 at 5:38 AM Matt Boiteau
> What are you guys running for exhaust? The thing is stupid loud and can barely talk on radio. Headset is LightSpeed wireless Tango's. Their ANR does not work well with the pitch of the rotary. Will try a Bose headset tomorrow.
> I have 2.5" exhaust leaving the cowl. (ex1.jpg) It comes down and centers the bottom of the plane into a 4" outer pipe. (ex2.jpg) The 4" outer pipe (5ft long) is open to the free air and exits behind the rear bulkhead. The 2.5" converts to a 3ft long perforated pipe (ex3.jpg) and exits inside the 4" outer pipe. For fun, I filled it full of ceramic fiber insulation mat, which did help a little until it blew all out.
> - Matt Boiteau
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