Hi Paul,

 I hope the  Oshkosh experience was very good.  The TTC project is
 very impressive.

 I’m gradually working through my radiator and oil cooler issues, and
 also building an exhaust header / tangential muffler.  I have a
 couple of questions on the latter.

 Please see the attached, although very crude, drawing.

 I am using the Racing Beat SS header, with short 2.5”x 1.75” OD .065
 304 SS tubes welded in place.  These will slip into 0.65” 1.88”
 tubes that will in turn be welded into a 6” 304 SS .065
 cylinder/muffler. On the front, a 90 degree 1.88” tube is used to
 reduce the length of the 6” tube and significant weight.

 Due to space and other constraints, I need to bring the 3” tailpipe
 (also .065” 304 SS) out of the *rear* of the muffler and up.  This
 gives me at least 3 options: 1. A straight 3” pipe welded to the
 rear of the muffler. 2. Squeeze the 3” tailpipe into a fish mouth
 (your previous drawings showed an area about 1/2 of that of the
 tailpipe). Or weld up a larger fish mouth. 3. Or, allow a short
 section of the 3” tailpipe to remain inside of the muffler, which
 could be closed off and drilled with (e.g. 0.5”) holes to arrive at
 the same exit area as the fish mouth design.  I am wondering if this
 might be a more conventional muffler design and possibly allow better
 sound reduction?

 The prior concerns regarding the longevity of any metal living
 “inside” the muffler have been noted. However, with a Renesis engine
 having exhaust ports coming through the iron housings, as well as a
 cooling tube, both giving lower exhaust temps, do you think this is
 a concern for .065" 304?

 Thanks for your input,

 Scott Gettings

 You are on the leading edge Scott. Nothing like this has been built
 yet. The RX8 side port exhaust is  a little cooler so it should work
 all right. If it burns through opposite the exhaust ports you can
 weld on doubler patches.


 Paul Lamar


 Scott,  Suggest that you investigate 321 S/s as 304 is a very low
 grade Stainless.  Remember the exhaust temp will get up to 1800
 degrees which is rather warm.  Your design is similar to what I made
 and is still alive, but I have not the cooling tube.  Neil Unger

 Nice work Neil.

 Paul Lamar


 Typically 309 & 310 are used for high heat applications, 309 is good
 for 2000F and 310 2100F. Be sure to use the correct filler rod the
 material you are working with or you will be wasting your time using
 these more expensive grades. I would not call 304 a low grade steel,
 they all have their place in the appropriate application. Andrew
 Campbell.


 Paul, do you recommend having slip joints on the pipes just after the
 SS flange like Scott has, or is it ok to put these further
 downstream. Reason is ask is that I wanted to duct some cooling air
 around that area in flight and my concern is when going from high
 power straight  to a power off, high rate of descent leading to
 possible uneven temps around the exhaust due to cooling air
 distribution.

 I want to try and minimize the risk of possible cracking. With the
 space I have to duct cooling air I have to duct it from front to rear
 so the front (if sitting in the cockpit) exhaust header pipe gets the
 coolest shot and the rear header pipe gets the air warmed by the
 other 2 further in front.

 Any issues you can see using thick wall stainless tubing bends

 Alex Molteno

 The thicker the wall the better. There is a weight draw back of
 course, .109 wall 304 and it hardly shows any problems at all. One
 can buy 304 SS hand rails from
 http://www.wagnercompanies.com/products-services/railing-systems-and-components/railing-components/elbows-and-wall-returns/
 <http://www.wagnercompanies.com/products-services/railing-systems-and-components/railing-components/elbows-and-wall-returns/



 rfq@mailwagner.com <mailto:rfq@mailwagner.com

 You can then use the exhaust plumbing for motor mounts :-) Joking of
 course. It is only the first 18 inches of a p-port or so and by that
 time it has cooled. The slip joint can go there. Scott has a problem
 in that it is a pusher so he has way less room in the cowl to work
 with. If you can avoid it keep the muffler out of the cowl and use a
 coax muffler.

 Do you have an RX8 engine? Things are a lot easier and quieter as the
 exhaust is a couple hundred degrees F cooler with the side exhaust.

 Paul Lamar


 OK thanks Paul, good to know for the parts source to use tubing
 handrail. I've added a bit of extra weight already during the build
 so a few extra lbs of exhaust weight will be OK for extra insurance
 against cracking

 Alex Molteno



Paul,

While studying the best configuration for the tailpipe on a tangential muffler, I came across another idea that might further reduce the noise:

If the combination of the Renesis exhaust being around 1600 degrees and a cooling tube might reasonably allow 304 metal to survive, do you think it might work to place the cooling tube INSIDE the tailpipe and let the exhaust augment the cooling tube air?  This would allow a lot more area for holes to be used in the “muffler” section of the tailpipe.  The inside of  the cooling tube only gets fresh air and does not mix with the exhaust  air until after exit.

In the attached  drawing both the exhaust and cooling tube go straight back, but would ideally need to exit vertically or at least at a 45 degree upward angle.  I assume  to have any augmentation the cooling tube would  need to extend past the exhaust exit flow.

If this is not still too far on the bleeding edge to make an educated guess, any suggestions are appreciated.

Thanks

Scott Gettings


Hard to say with out spending a lot of money on instrumentation and data recording.

Paul Lamar

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