I have the free Decibel Ultra, but it only goes to 120 db.  Not nearly high enough!

 

My plane doesn’t seem that loud inside in flight although people on the ground recognize me from afar.  You might consider some soundproofing on that aluminum skin around the exit of the exhaust.  My plane is fiberglass and inside in flight it sounds like Tracy describes it as a hum.

 

I use the Lightspeed Mach 1 headset.  It is the in the ear headset and doesn’t have noise cancelling, but seems to work as well as those that do.

 

---

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of shipchief@aol.com
Sent: Sunday, January 19, 2014 12:05 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: muffler for Renesis?

 

Charlie;

The turbo does strip off a lot of noise. I understand the unmuffled 13b will rip your ears off!  ;)

Still, at power above 5000 RPM it is too loud for me in the cockpit, and I'm wearing a Flightcom copy of a David Clark headset.

I'm planning to download a Decibel Meter app for my IPhone once I remember my password....

I'm leaning toward the SPLnFFT app, which has a good rating.

It will compare the sound volume and quality of my future muffler attempts.

 

-----Original Message-----
From: Charlie England <ceengland7@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sat, Jan 18, 2014 12:00 pm
Subject: [FlyRotary] Re: muffler for Renesis?

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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