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Engine basics => Engine set up tips => Topic started by: Tim Wescott on September 13, 2013, 11:04:16 AM
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I know I've seen bits and pieces of this information come up before (it may even have been me asking), but I can't seem to find it in a search.
What's a reasonable figure to expect for the temperature of a glow engine muffler? Or is this one of those "it depends" sorts of thing?
I've had occasion to want to make custom mufflers, and I'm wondering what materials I should be limiting myself to. CF-epoxy would be kewl, but not if it burns off the engine. Making up aluminum bits on my lathe and sticking them together is attractive, too, but I have no facilities for TIG welding. I've tried oxy-acetylene welding aluminum with little success -- I'm wondering if aluminum solder that's good up to 390F is going to hold together.
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Hi Tim,
I have seen tongue mufflers that were pinned and JB "Welded" which have held up quite well.
BIG Bear
RNMM/AMM
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I'm too lazy to try it, but how about an entire muffler molded of the vinyl or rubber compound used to make the DuBro exhaust extensions? If you make an aluminum barrel muffler really light, the sides get thin enough to transmit engine noise. I got as far as trying the commercial handle dip compound on a foam mold. It will take 4 or 5 applications, and it delaminates when you treat it with acetone to melt the foam pattern. So the next step is to make a mold, coat it with release, and make a soft muffler. Then devise a clamping setup to hold it either to the exhaust stack or an extension bolted in place. I have had no problems with JB Weld used on an aluminum muffler so long as it is 2 inches or so away from the exhaust outlet. Never had the urge to try it any closer.
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So -- try it and see what falls off?
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Silicone rubber is good to some 500F. It can be had in caulking tubes (make sure it is 100% silicone). If you make a "paper" mold for it, and then let it cure for a few days. The mold should dissolve in water. I would use soft tissue (toilet) paper with some harder paper (tape? gift wrap tissue?) over it and keep the material thicknesses below 1/4 inch.
You can use white glue to join "cores" and components together.
Using some release agent (wax) on metal cores that are small enough to flex out with the assistance of air or water pressure would offer better dimensional tolerances.
No I haven't tried this for making a hollow component. I probably should.
Sugru
http://sugru.com/
and reading about "cloning" the material by mixing corn starch and 100% silicone is what I have tried with mixed results (long cure time)
I wouldn't want filler material in the mix exposed to high heat.
Phil
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I'm too lazy to try it, but how about an entire muffler molded of the vinyl or rubber compound used to make the DuBro exhaust extensions?
We have one plane flying control line at my field with one of those extensions. It flaps in the breeze, and makes it sound like the plane is blowing a five minute raspberry.
That would certainly add an interesting dimension to the whole tongue muffler experience.
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It might be interesting to make a soft muffler for profiles which aims straight down, with a stinger that terminates say about 3" below the exhaust stack, to help reduce oil accumulation on the plane. A soft muffler could probably withstand nose-overs on a 2-wheel plane better than a metal one.
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The two things that made me curious about it are that the soft material can be sound deadening instead of transmitting, and much more crashworthy than a rigid muffler. Or combine it with a surgical tubing venturi extension to keep dirt out of both the intake and exhaust when terra firma contact occurs.
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If terra is firma enough, dirt intrusion is the least of your worries.
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Long rough grass gives us the hardest time keeping the nose up where it should be on takeoff and landing. As for crashes, I saw a friend slice an engine in half on the pavement at VSC.
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I've been hoarding the large aluminum Sharpie marker tubes for a muffler experiment, just don't have the resources to weld ? some kind of attachment point for the engine. Tim I'll send you a couple if your interested.
Steve
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Thanks Steve. That's not what's on my mind at the moment, but I may get back to you.
Those markers are small enough that you may not be able to weld 'em.
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Hello.
I have tested quite many aluminium brazing products and without doubt the best is Castolin Eutectic #190. It can be both brazed with a gas flame (or owen) or TIG welded. I use a normal butane (?) camping gas blow torch for perfect results every time.
I use brazing to assemble the end caps, the back end is turned to 1/64" wall thickness and the front part has a bit more, maybe 1/32" wall thickness.
For joining the end caps to center tube I use JB weld. No problems after hundreds of flights. The center tube is dural tube with 1/64" wall thickness.
Lauri
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I tried my silicone caulk idea and made a stretch on bee muffler for a cox .049. It works OK but looks like a glue turd. (am I allowed to say that here?)
I used a 7/16 bolt, wrapped a layer of gift wrap tissue paper over it and taped the ends. I then wrapped a thin strip of the same tissue (ok, about 10 strips stacked up) so I had a rib 1/4 inch wide and the total diameter was 3/4 inch (so it would easily stretch over the engine head) I then wrapped some of the same gift wrap tissue around a pin till it was 3/16 inch diameter, and pinned it into the buildup ring on the bolt. I moistened with water to hold everything in place.
Next I applied 100% silicone caulk to the paper form. I clamped the bolt in a vise and left it. The caulk surface cures in about an hour, and is actually solid through much of the thickness. Being wrapped on moist paper helps cure the inside, and also allows for easy release at this point. Pull the pin, pull the paper out, slide the whole assemblage off the end of the bolt, and unwrap the paper from inside. I then let it sit for a couple days to finish curing.
I was generous, although if I do this again I am using paper disks and tubes to control the caulk.
Trim the excess, and pop it on. It works well...even though it is ugly. I was concerned about how much heat the caulk was retaining as the engine seems to run hotter than normal, and the muffler became too hot to touch very quickly. The crankcase seemed to be "normal" temperature but it acted like fuel was boiling in the 8cc bee tank near the end of the run.
I have pictures but the computer isn't cooperating right now.
Phil
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(http://i76.servimg.com/u/f76/17/84/87/39/th/img_2041.jpg) (http://www.servimg.com/image_preview.php?i=74&u=17848739)
(http://i76.servimg.com/u/f76/17/84/87/39/th/img_2040.jpg) (http://www.servimg.com/image_preview.php?i=73&u=17848739)
Heh, more than one way to skin a cat, so to speak...
Phil
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Phil -- that's a neat idea.
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Yes, but it looks obscene. LL~ LL~ LL~ LL~ LL~ LL~ LL~Hey, what ever works.
Best part is I can pop it on when needed and hide it in the box when not.
Yes, it looks horrible looking, n~ but it is also an experiment to prove it works. :!
Phil
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You can get two-part silicone casting resin, so you don't have to wait a long time for stuff to set up. It has two interesting properties: 1) it has a super high coefficient of thermal expansion, and 2) if it's confined and heated, it's gonna expand regardless of what's in the way. You could use it to make a better-looking muffler than Phil's (although his looks pretty cool), but it would probably fall off when it got hot.
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I had some retained paper char during my run, but the silicone is still in perfect shape. (yes, only 1 run) If a metal attachment is used to the engine, which will allow slight cooling of exhaust gasses, I expect there will be no long term problems.
I looked up 2-part products and I seem to only find kits in the $100 and up range (Fine, I didn't look too hard). For FREE (I used an open tube leftover from the new bathroom sinks) I think my results are pretty meaningful.
Red or "copper" high temperature automotive RTV gasket maker can be substituted at low effective cost for a small number of parts (less than $10 per tube, any auto parts store).
Phil