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Date: Sun, 01 May 2005 09:18:01 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Inserts
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Ed Anderson wrote:

>
> > Not directly applicable here except in the sense that we should make no
>
>> untested assumptions, but here goes:
>>
>> Kent Paser of 'Speed with Economy' fame played with 'reversion cones' 
>> on his Lyc. They are cones smaller in diameter than the exhaust ports 
>> & mounted directly in the ports. Obviously this should interfere with 
>> exhaust flow but he found that they can improve breathing in a Lyc.
>>
>> The NA splitters look suspiciously like flattened cones....
>>
>> To invert Bob's tag line: when things change, things change.
>>
>> Charlie
>> (just stirring the pot a little)
>>
>
> Ok, "Pot Stirrer"{:>).  The reversion cones in exhaust are designed to 
> do just that as you are aware.  Prevent the reflected pressure wave in 
> the exhaust from pressurizing the cylinder while it is open for the 
> intake function and hindering intake of fresh fuel/air. However the 
> only  Mazda engineering data that I could find indicated the primary 
> purpose of the "splitters" are for noise suppression. Here are two 
> charts on the Mazda Exhaust splitters.  The technique appears to be 
> more effective at the higher rpms and as Tracy and I speculated, 
> probably has little effect on power until the higher rpms.  From the 
> chart, it looks like the technique is really effective after 4000 
> rpm.  So if it is at the same time affecting power, it may be 
> happening at lower rpms than I originally would have thought.  Here 
> are the two charts.
>
> 7-207.gif shows the splitters  and 7-208 shows the 8 db noise 
> reduction obtained by use of the splitters.  I believe the tuboblock 
> has no splitters because it has the turbo to deaden the exhaust noise 
> - if the splitter were for reversion prevention then I would think the 
> turbo blocks would have it as well.
>
> Not conclusive proof, but the only data I could find on the function 
> of the splitters.
>
> Ed A 


I love it when a plan comes together. I got Ed to show me previously 
unseen hard data on how effective the splitters are at noise reduction. 
:-) Now I need to know how much hp is really lost. In order to determine 
that, I need 1st to know how the difference *using the same exhaust 
system*. Then I need to know how much is lost in the extra 'muffling' 
needed to reduce the clean ported system by 8 dB. Then I need to know 
how much weight is added by the extra 'muffling'. Then how much drag is 
added by the extra muffling hanging out in the airstream.  I think Tracy 
said that his current belly mounted muffler is costing somewhere between 
3-5 mph. Looking at the cube function of airspeed/hp, how many hp does 
it take to recover 5 mph at 200 mph? Can I arrive at the same net 
performance with a smaller in-cowl muffler & some careful heat shielding?

BTW, Bill's right about the name & design details (expanded pipe around 
the cone) of Anti-reversion cones. Again, a plan comes together as I 
learned more new stuff. I knew the design details but wasn't aware of 
Jim Fueling. Thanks, Bill.

Sometimes dumb questions (or statements) yield some pretty intelligent 
thoughts & useful data. Onward, through the fog...

Charlie