My 2009 Muffler Design Mods

[Cincinnati Joe]

In addition to all the great friendships, fun, competition, and burning events, I also like to mess with Muffler design. This will be my 5th design change in 4 years. Last season I got 10's for sound at EVERY event, but lacked power on up lines during the hot humid July/August timeframe. I was using .75 OD aluminum tube for headers and muffler inlet. I thought this was enough, but have never been able to duplicate my 04 design that seemed to provide a "boost" (it was in "Plum Crazy" Staudacher). I went back to that design and realized it had a 7/8 ID inlet tube. Since I was unable to find pre-formed 90 degree radius bends (for my exhaust headers) I went with 1 inch OD X .060 wall 6061 aircraft aluminum. This is SURE to let the engine breath better!! I also had an opportunity to examine the inside of one of Brian Sanick's mufflers when I had the good fortune to help him with a repair - the "diffuser" disc was VERY close to the front end of the stinger chamber and did not touch it at all - it had an .060 gap between a solid disc and the outer muffler tube. I know that weapon silencers use SLOTS for most effective sound abatement, so this time around I'm trying SLOTS around the periphery of the diffuser plate (see picture). The net area of the slots is about 20% less than the 1 inch tubing, but still AS LARGE as the exhaust port cross section on the DA100 heads. All that's left is to try to TIG it all together without blowing any holes in the parts! Can't wait for Spring to try it out! (the dark furry creature is my muffler design advisor, "Binky") The main tube is a "recycle" of the "ring-ding-ding" muffler design flown in 05. No wasted parts in this man's shop! Going to stay with the Aeroworks YAK again this season. I've almost got it trimmed now...

[Yakov]

Joe,

The design looks interresting.

I've subscribed to the thread to see what your results are.

What are the dimensions of the main can?

Of course you should stick with your Yak... You know.... Once You've flown a Yak...... you NEVER go back!

[Cincinnati Joe]

Overall dimensions are 12" L X 2" OD. Tube is .035 wall 6061. Back chamber 10 inches, Stinger chamber 2 inches. End pieces are machined cones with 20 Degree angle. Inlet is 1 inch OD .060 wall, and stingers are 3 inch X 5/8" OD .042 wall.

[Cincinnati Joe]

Yesterday I had the parts all finished up. I put the diffuser disk in the body tube and blew through the center hole, and it had some "backpressure" (as compared to blowing through a "Grieves") so I added the two round holes, which brought things where I thought they should be. I figure maybe the two round holes will make some extra turbulence and mix things better in the stinger chamber anyway... It was about 40 today, so I raised the garage door about 6 inches for ventilation and went at it. TIG welding is truly an art, and I've trashed a lot of thinwall aluminum tube to get to where I'm at... I'm a BSEE by training, and TIG welding is kinda like riding a bike - I can explain all day about how to do it, but until you figure it out by doing it....

Anyway, the welds are definitely a bit on the ugly side, but they hold the stuff together well, with no leaks. The two mufflers are only 4 ounces heavier than my set of stock BME pieces (I don't have a set of stock DA mufflers...) so I figure I did OK. Now I've got to get started on the aluminum headers to match up with the mufflers!

[Imac Kiwi]

Very interested in your results.

[flying skunks]

[Cincinnati Joe]

The 1 inch OD "L"s are from Woolf aircraft products (full scale stuff) and run 20 bucks a pop. After forming, they are brought back to 6061 temper. They come with 12 inch "legs" that need to be cut down. Got that done. All work here is done with hacksaw, file and "Unibit" from harbor freight. This is what I accomplished today after work. I'll have to "build up" (with the TIG welder) a bit on the inside of the Header plate on either side of the .88" tube ID to properly seal along the edge of the more or less square exhaust port - but it was easier to drill and fill, then try to form a square out of the round pipe and screw with the wierd hole in the plate. In the other direction, a diamond burr will let me "blend" the exhaust into the tubing. Really no better or worse than the do-it-yourself stuff from KS, and probably a lot stronger. I drilled all the holes in the plate before cutting apart with my hacksaw so it would be easier to handle. No machine tools in my shop!!

[sTACYLLOYD]

one of thees times when i come down to your contest i will walk you through how to tig weld it looks like your spending to much time in one spot getting it to hot. looks good though

[Cincinnati Joe]

Had one helluva crappy time at work today, so coming home to this project was the best therapy I could find. Finished cutting the 1/4" thick flange plates for the headers, lined them up on the airplane and "tacked" the pipes at the perfect angle for a dead-straight shot into the mufflers. Then removed them, welded the top side, and flipped them over and "filled" the two sides of the circle on the face. Used a diamond coated ceramic tile cutter bit in my Dremel to carve out the "blend" between the port outline and the ID of the tube. Then did some hand filing and finished up with some 320 wet/dry sandpaper on the blend and then "plate-sanded" the face to true it all up. Welding was maybe a 20 minute job, including fitting and doing the fill-ins. Shaping that cylinder port shape to match the DA was about an hour job by hand. Yeah, lots of work, but I enjoy this kind of stuff - it's a change from gluing balsa together or monokoting a big bird. I'll tackle the other side tomorrow...

[Cincinnati Joe]

Started work on this project last Saturday. A couple hours every day since, and the mufflers and headers are now done. I discovered I could remove material and get a better blend using a small, fairly rough round file. All that's left to do for this season now is install a lighter tank - 1 litre rectangular vegetable oil bottle - saves 4 ounces over stock heavy wall nylon tank - and replace the wheelpants (3 times repaired and repainted) with balsa/ply "spats" - another 6 to 8 ounces (or more) weight savings. Less weight, more power. Wooo Hooo!

Anyway, this is pretty much the end of this project - testing will have to wait till Spring, or an unusually warm day with dry conditions on our postage stamp sized field in Newtown, Ohio.

Here are "before" and "after" shots. All the stuff in the first picture is my effort too - but I had some professional help on the muffler welding (it's pretty obvious...).

Just remember, you can do prettymuch anything if you put your mind to it! I can't wait to see the improvement in the uplines!!

See you at the flying field!

[Cincinnati Joe]

I mentioned another design earlier... I had the chance to have a few more "washers" machined, and cut the front off last season's mufflers to recycle them. I fabbed the new inlet assembly shown below. It should accomplish 2 things: 1) it make the construction much easier - just three "washers" now - inlet, diffuser and back plate. 2) it might increase the efficiency, since instead of "slits, slots, or holes" in the diffuser, there is just one uniform "slit" formed by the gap between the OD of the diffuser plate and the ID of the main body tube.

This might increase the efficiency, since after expanding and cooling in the expansion chamber, the gases will flow symmetrically around the diffuser plate into the stinger chamber. This will undoubtedly present a smoother flow profile than the slits, slots and holes in the other diffuser design.

I'll test both designs this Spring, monitoring static RPM, head and exhaust gas temps, and noise level DB, as well as subjective "tone". I prefer the old "thrush" sound from the 60's

I realize that there could possibly be some advantage to "tuning" the length of the header, but I'm not willing to put in the time in that area. Perhaps if someone has the time and resources to do some header length testing, I could provide a set of mufflers in exchange for the time and test data you would generate...

[sideways312]

Im glad to see that NC has people who love to experiment

[Cincinnati Joe]

My friend Toby asked about getting a couple of this design, but "a little longer". I also increased the outlet stinger to 7/8" OD, since he plans on using these on the 85CC single cylinder motors. Can't wait to see the results. The design is a little different, in that the stinger "chamber" is at the back, and the front inlet opens directly into the main chamber. Curiously, with the stinger plugged with a finger, and blowing over the inlet port, the longer design with the stinger chamber at the rear, resonates at a HIGHER pitch!! Any physicists out there care to postulate a theory of why this happens?

[Cincinnati Joe]

The answers are all in. I've flown both designs. The last one I talked about, using a solid diffuser disk, is just a tiny bit louder (barely 1 db) but flows much freeer (is that a word??) i.e. it has significantly less restriction. Not enough RPM difference to notice with an analog (needle) tach.

[Cincinnati Joe]

Still making changes. I extended the stinger chamber by 2 inches and increased the stinger OD by 1/8 inch to 5/8. It's hard to hear the mufflers above the ripping of the prop! My welding skills are improving as well!! Beads are getting smaller!