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Just to be clear, I'm looking at the H
P resonator, not the full size muffler.
http://www.summitracing.com/parts/hsh-12412400/overview/
I would either use that, or the aeroturbine without the built-in
resonator:
http://www.aeroexhaust.com/mufflers/aero-exhaust-at2525.html
If you've never heard Dennis Havarlah's Renesis in his RV-7A, you
can barely hear the engine. Most of what you hear is prop. He uses
the stock Renesis exhaust manifold, which feeds at a tangent into
a large diameter 'swirl can', which has a tangential exit into the
H P resonator. Note that *all* of that is within the cowl. There
is a lot of empirical evidence that the extra mass and damping
material between the layers of metal in the stock manifold does a
lot to kill the offensive odd-harmonics in the exhaust tone.
Keeping everything inside the cowl seems to help a lot, as well.
My belief is that the high freq audio energy that survives &
radiates off the manifold & muffler gets damped further by the
cowl, so what's left is a much more pleasing, lower frequency
spectrum sound.
I would have expected your turbo to strip off most of the high
freq energy. Can you find a sound level meter to quantify what
you're hearing in the cockpit? (And don't forget, the prop can be
very noisy, too. If you're running a 2.1 ratio drive & turning
a fairly large diameter prop, that may be the source of some of
your noise.)
Charlie
On 1/18/2014 1:10 PM, shipchief@aol.com wrote:
I'm running a turbo, and it's still pretty loud. After I
take off and climb out, I find myself reducing power to reduce
the sound level.
It's pretty quiet at idle and during ground operations, but
above 5000 RPM which is above 34"Hg manifold pressure, it's
too loud inside the cockpit for me.
My TO4 turbine outlet faces aft into a reducer cone
transition to a 2" pipe. This pipe has two 90 degree bends and
lets out parallel to the air exit ramp on the bottom of the
fuselage of my RV-8.
I'm thinking the sound waves need to be directed away from
the fuselage skin, so I ordered a slip on exhaust turndown tip
(Walker 41420) and a lap joint band clamp.
Even with that, I would like to be a good neighbor. I'm
planning to flatten the turndown to a 1" rectangular outlet,
and drill 18 ea 3/8" holes in the down facing flat. Then use a
3/8" diameter rod to bend each hole into a slightly rear
facing shape.
I believe the term is "Piccolo Pipe".
I have a Hushpower muffler, which I bought after Tracy made
his first report on it. I just checked it out (box is pretty
dusty, time must have slipped by somehow?) That thing weighs
alot. Also, the idea that the 'innards' might break loose and
clog the outlet seems a bit scarey.
The Aeroturbine would look better hanging under the
fuselage tho- if I end up needing a real muffler. (might need
to clamp on 4 big fins at the back for aerodynamic guidance
+ asthetics?)
-----Original Message-----
From: Charlie England <ceengland7@gmail.com>
To: Rotary motors in aircraft
<flyrotary@lancaironline.net>
Sent: Sat, Jan 18, 2014 9:23 am
Subject: [FlyRotary] Re: muffler for Renesis?
Thanks, Mark. I discovered that after I sent the previous message. Their
web site seems to have a somewhat random 'organization'.
Is the non-res model only 20" overall, as they describe? That would make
it only slightly longer than the H.P. resonator that Dennis is using, &
since it appears to be only a perforated tube in the main cylinder, it
should survive much better than anything with actual baffles and/or packing.
Charlie
On 1/18/2014 9:38 AM, Mark Steitle wrote:
> Charlie,
> They stock two types, one with packing, one without. The one with packing is
their "resonator"model, and it is longer than the non-res model. I bought the
non-res model as I figured the packing was only temporary. I have not installed
it yet, so no flight report.
>
> Mark
>
> Sent from my iPad
>
>> On Jan 18, 2014, at 8:54 AM, Charlie England <ceengland7@gmail.com> wrote:
>>
>> Thanks, Tracy; it's good news that it is both quiet and survives. Didn't
realize that the aeroturbine had packing in it. If it performs as well as, or
better than the hushpower, I may give it a shot. It's actually a bit cheaper
than the h.p. resonator.
>>
>> Charlie
>>
>>> On 1/17/2014 10:53 AM, Tracy wrote:
>>> The aero turbine sounded better than the Hushpower II but both change in
tone over time, probably due to packing deteriorating. Still, the AT was the
best after they stabilized.
>>>
>>> Tracy
>>>
>>> Sent from my iPad
>>>
>>>> On Jan 17, 2014, at 11:06, Charlie England <ceengland7@gmail.com> wrote:
>>>>
>>>> Time to order a muffler. My goal is to keep it inside the cowl (RV-7). I
know, I know, but it looks better, and more important, it *sounds* better.
>>>>
>>>> I believe that Dennis H. used this:
>>>> http://www.summitracing.com/parts/hsh-12412400/overview/
>>>> I know it sounds great. Dennis, do you remember the weight of just the
resonator?
>>>>
>>>> I know that Tracy is running an Aeroturbine (weight: 6 lbs on the 20B in
the RV-8, & has talked about how good it sounds:
>>>> http://www.aeroexhaust.com/mufflers/aero-exhaust-at2525.html
>>>>
>>>> They are roughly the same size and price, so I'm wondering how the
Aeroturbine will compare in performance (meaning: killing the harsh harmonics of
the rotary).
>>>>
>>>> Tracy, you might be the only person who's heard both on a rotary. Based on
your 20B experience, is it likely to work better than the Hushpower Resonator on
a Renesis? I'll be using a manifold/transition pipe similar to Dennis' setup to
keep everything inside the cowl.
>>>>
>>>> Thanks,
>>>>
>>>> Charlie
>>>>
>>>>
>>>>
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