Mailing List Message #65382
From: Charlie England <>
Subject: Re: [FlyRotary] Re: Mufflers
Date: Wed, 20 Nov 2019 12:24:59 -0600
To: Rotary motors in aircraft <>
On 11/20/2019 10:22 AM, David Leonard wrote:
I am really glad you brought up the Mistral incident, as I have been meaning to mention it too.  For what it's worth, my experience with mufflers confirms what many other have said.  The exhaust environment in rotary aircraft is very extreme and component  failure can be catastrophic.  I have tried several types of high end packing, and nothing survives more than a few hours.  300 series stainless tolerates the heat, but any welds on thin stainless have limited life.  I would be very suspicious of anything with complex innards like the Aero Turbine 2525.  Doing what Jeff Whaley did by adding perforations should be a must-do in my opinion.

Dave Leonard

On Wed, Nov 20, 2019 at 5:59 AM Marcus Wiese <> wrote:
Just remember the Mistral muffler event. The muffler caused the Piper Arrow  (?) with their rotary to crash after the internals blocked the outlet and led to power loss. It may have partially led to their withdrawal from the engine/PSRU market. To all our loss.

Sent from my iPad

On Nov 20, 2019, at 12:28 AM, Matt Boiteau <> wrote:

This is the Aero Exhaust 2525XL diagram. I have one, but left it in Canada. Will bring it back with me in Jan to try at taming the exhaust again.

- Matt Boiteau

On 2019-11-19 3:23:50 PM, Charlie England <> wrote:

On Mon, Nov 18, 2019 at 11:57 PM Andrew Martin <> wrote:

Kelly, I would if I had some, really did not expect it to work as I deviated from the design a bit. Will be back at airport on weekend to take photo, too late for construction photo. But nothing to it.

I read about the idea by Gary Schwarz in this thread, post #7 , post #58 for his testing and post #142 sums up his findings.
Someone on here may know him as he was doing it for a rotary. Mine is much shorter than his drawing below due to space constraints but the theory works.
edit: Ahh!!! deleted his picture as too big to post. it is in his post #7 mentioned above though.

That looks a lot like a simplified version (one less turn) of a standard automotive muffler.
The Aeroturbine tries to achieve similar effect (without the flow reversals) by using venturi effect to suck part of the exhaust around and then back into the central tube.


Archive and UnSub:
The caution about potential blockage is warranted on any engine, but obviously a greater danger with the rotary's powerful pulses.

It's worth mentioning that the Renesis' exhaust should be significantly less 'violent' than a 13B, for a couple of reasons. The exhaust has to take a 'sharp right' as it exits the combustion chamber, which helps break up the shock wave a bit, but even more importantly, the exhaust port, instead of 'snapping open' like a piston ported two stroke, opens more gradually, more like a conventional poppet valve in a piston engine.

As a FWIW on the Aeroturbine: I don't have a 2525XL to examine, but the regular 2525 (minus the 1st chamber of the XL) is a 'straight through' design. That cone on the input end is open. Drawing of the guts is on the Aeroturbine web site.

IIRC, Tracy's been flying one on the 20B powered RV-8 for a number of years. That's what motivated me to purchase one, but it hasn't seen any exhaust gas yet.

Subscribe (FEED) Subscribe (DIGEST) Subscribe (INDEX) Unsubscribe Mail to Listmaster