Re: a cheap sport muffler

roddie Thu May 04, 2017 10:19 pm

fit90 wrote:Roddie,

I definitely get the experimenting and learning part of playing with our little engines. I think that is where most of the fun lies. We are constantly coming up with new and unique ways to accomplish the same tasks. I look for ward to following your post and seeing how it goes.

Bob

Thanks Bob, I'd really like to "prove" this muffler design.. which is why I posted this pressure-tap note here. The muffler itself needs more testing. My design provides a huge variety of variables to be explored. Even in the full-flow configuration.. it offers slight noise-reduction.. with the benefit of routing the exhaust-wastes directionally (preferably downward..) to help keep the airframe from getting covered with oil-spray. I hope to prove other advantages.. such as the aforementioned tapping for fuel-pressure feed.. and possibly the scavenging of exhaust, through the use of dual-headers having differing-size openings in the pipes. Maybe other benefits can be realized as well. Who knows. Muffler technology hasn't really been explored with the Cox .049 engine. I'll try to document my findings this season.

roddie Fri Jun 30, 2017 12:17 pm

Most of us know that running our Cox engines and other IC engines (especially 2-strokes..) poses noise that's likely to be objectionable in a residential setting. One of my personal conquests is to reduce this noise.. with a minimal performance penalty.

Landscaping-companies typically run noisy 30cc 2-stroke weed-whackers/edgers/leaf-blowers when doing somebody's lawn.. and the neighbors don't complain.. because the end-result is the beautification of the neighborhood. (just thought I'd mention that..) Laughing

Many of us are C/L fliers using Cox engines. We didn't used to have to fly at a secluded/remote location.. although "now"; we've been conditioned to the fact, that this is the only acceptable way to do it.. without disturbing people.

I'll be testing my muffler-design hopefully over the next week.. but I don't really have a method (other than my own ears..) to accurately measure noise-reduction. Performance on the other hand, can be checked by using a tachometer.

My muffler has the means of running a single minimally-restrictive header-pipe out of a chamber that encloses the exhaust-ports on the Cox engine cylinders. It's therefor possible to connect an extension-pipe routed to a small canister packed with steel-wool. Something like a plastic eye-drops bottle that can be mounted to the underside of the wing, to further reduce noise with less restriction to flow. The whole system can be surprisingly lightweight.. depending on the materials used. The idea is to deflect the sound-wave. Running any engine "open-face" will send the sound-wave out in a wide-spread pattern with zero augmentation. Deflecting the sound-wave will re-direct it.. but not necessarily augment it. It needs to be contained like any muffler functions. Tuned-pipes have no packing/inner restriction.. yet they do a good job with noise-reduction by enclosing/containing the sound-wave.. as well as "increasing" exhaust-velocity for more power.

I don't know if running an extension-pipe to a steel-wool/glass-packed chamber will offer any noise-reduction.. but it's worth giving a try.

KariFS Fri Jun 30, 2017 4:21 pm

Roddie, if you or your wife have a smartphone, there are noise meter apps available. I have one on my iPhone, it is not a precision instrument (can't do "certified" tests with it) but it is helpful.

roddie Fri Jun 30, 2017 6:08 pm

KariFS wrote:Roddie, if you or your wife have a smartphone, there are noise meter apps available. I have one on my iPhone, it is not a precision instrument (can't do "certified" tests with it) but it is helpful.

Thanks Kari.. that's a good suggestion! It would be interesting to know just how much quieter I can make the engine run.. by having some sort of meter. I used one of my mufflers on my Ace throttle vid.. and when the engine was puttering at 3K.. it was pretty quiet. The muffler had dual full-flow pipes on it though. When throttled-up, it was noticeably louder.. but a little bit less noisy than if I was running open-face exhaust.

I don't really know yet; how much sound-insulation that the muffler actually provides. There may be some "blow-by" through the rubber body.. which could increase when running smaller-diameter pipes. We'll have to see what happens there. I haven't run any smaller-diameter pipes yet.. and neither have my two buddies whom I sent muffler-kits to...

roddie Thu Jan 03, 2019 6:35 pm

A recent thread; "SPI or Free Porting" revived a thought that I've had for my muffler design. We know that SPI doesn't work well with conventional mufflers.. because spent gasses get sucked back into the crankcase.. rather than the fresh air from running the engine without a muffler (open-face).

One of the features of my muffler design is an optional expansion-chamber having dual-outlets spaced 180 degrees from one another. The pipe-inserts which fit into these outlets can have different size orifices.. which could result in a cross-flow (scavenging) which could (in theory..) pull fresh air into the muffler through the smaller-orifice pipe. That's a lot of "coulds"... Laughing

roddie Wed Jun 23, 2021 8:24 pm

I'm going to resume engineering-work on my design.. with an emphasis on muffler-pressure-assisted fuel-delivery.. or "MPAFD". Smile

This might be of some use to those running external fuel-cells. The Cox .049 "Postage-Stamp" backplated product-engine's used external tanks. The later "horseshoe" backplated product-engines used external fuel-tanks. Your "Killer-Bee" uses one. Your hot-rodded carb.....

roddie Wed Jun 23, 2021 9:32 pm

Lynne and I will be on holiday/vacation early July. We're headed for Sturbridge, MA to visit Brimfield, MA.. home to the Northeast USA antique/flea-market scene. I'll take photos.. and will be on the look-out for 1/2A stuff.

Hog Heaven Hobbies is in the "Fiskdale" village of Sturbridge. Our last trip there was December 2017 on our 10th wedding anniversary. I asked about Cox/consignment sales-items and was shown two lots. I purchased the larger lot for the tagged/sticker-price of $50. In that bag were a Cox Tee Dee .09, a Tee Dee .049, a Medallion .049, two (X2) Golden Bee's.. two postie-product engines (complete w/fine-thread NVA's) and a couple of WenMac/Testors FRV .049's.

I'm going to ask about the other (smaller) lot.. to see it it's still there.. Twas a couple of Cox .049 engines.. but @ considerably more $.

Yabby Mon Jul 05, 2021 4:12 pm

Hi Roddie,

You are probably still traveling and hunting for bargains! I wish we had huge flea markets like you guys and they do in the UK also I believe. We have them, but not the sort you fellas describe. Anyway, have you tried your muffler with a Tee Dee cylinder? I guess I should make one and try for myself. lol!

I like the idea of the pressure line going to the bottom outlet of the wedge tank and blocking the top one. I tried using pressure via an extra hole and a pop rivet in a standard Cox muffler and found it introduced bubbles in a wedge tank on a standard horseshoe Surestart engine. I will try reversing the pressure connection and see how it goes. I also found the engine tended to have a resonating sort of high/lower frequency when running with the pressure from the muffler. It didnt just rev smoothly. The revs up the top would like flutter maybe just a couple of 100 rpm, and I wondered if it was caused by the pressure wave of the single cylinder.

Great thread Roddie, I must get a good muffler working with my TD cylinders, The noise sadly is now unacceptable. I am thinking of shimming the base of the TD cylinders to remove the SPI. I hand made a shim for the base of one and found the Tee Dee ran really well with a muffler, when the SPI was shimmed out. It ran much better than a TD with SPI and the muffler anyway. The problem for me with base shimms is they are (for me anyway) really hard to make. I havent tried drilling the between clamped metal sheets yet. Maybe that will work. And I havent seen any for sale.

Its middle of winter here! not great for flying, but good for these types of experiments before flying weather comes up.

Thanks for your work Roddie and for the effort to publish it so well.

Yabby

getback Wed Jul 07, 2021 6:56 am

Yabby here is a good read on timing shimming and performance >> https://www.coxengineforum.com/t11626-cylinder-shimming?highlight=Shimming++049+cyclinders /// https://www.coxengineforum.com/t13945-shimming-cox-cylinder-for-transfer-and-exhaust-timing?highlight=Shimming++049+cyclinders Seems like someone said you could use .09 head gaskets to shim .049 cylinder , But who is selling those now ?

Yabby Thu Jul 08, 2021 7:30 pm

Hi Getback,

Thanks for the response and links! Thumbs Up

The information was very helpful and confirms my technical understanding and some experiments I did with some very poorly made homemade shims I knocked up at home. I run both Reedys and TDs all 049. And always have to run a muffler other than when Im up at the shack out bush a bit. cheers

I have found the original slitted cylinders tend to perform quite well for my purposes with a muffler, but the TD cylinders on a Reedy or TD with a muffler really not so well. Im ok with the muffled performance with a shim as the choice is no performance cos I cant fly. I have several different head types I can use on my engines also to experiment with in combination with the shims, cox heads/plugs, standard glo plugs, and turbo plugs, so I reckon once shimmed I will find a combination most likely that works for me with TD cylinders for my flying needs. Beer Cheers

Yabby

roddie Thu Jul 08, 2021 8:10 pm

Yabby wrote:Hi Roddie,

You are probably still traveling and hunting for bargains! I wish we had huge flea markets like you guys and they do in the UK also I believe. We have them, but not the sort you fellas describe. Anyway, have you tried your muffler with a Tee Dee cylinder? I guess I should make one and try for myself.

I like the idea of the pressure line going to the bottom outlet of the wedge tank and blocking the top one. I tried using pressure via an extra hole and a pop rivet in a standard Cox muffler and found it introduced bubbles in a wedge tank on a standard horseshoe Surestart engine. I will try reversing the pressure connection and see how it goes. I also found the engine tended to have a resonating sort of high/lower frequency when running with the pressure from the muffler. It didnt just rev smoothly. The revs up the top would like flutter maybe just a couple of 100 rpm, and I wondered if it was caused by the pressure wave of the single cylinder.

Great thread Roddie, I must get a good muffler working with my TD cylinders, The noise sadly is now unacceptable. I am thinking of shimming the base of the TD cylinders to remove the SPI. I hand made a shim for the base of one and found the Tee Dee ran really well with a muffler, when the SPI was shimmed out. It ran much better than a TD with SPI and the muffler anyway. The problem for me with base shimms is they are (for me anyway) really hard to make. I havent tried drilling the between clamped metal sheets yet. Maybe that will work. And I havent seen any for sale.

Its middle of winter here! not great for flying, but good for these types of experiments before flying weather comes up.

Thanks for your work Roddie and for the effort to publish it so well.

Yabby

Hi Yabby, Sorry to be late to reply. Thank you for your interest in this thread. I haven't tried my design on the Tee Dee or Medallion .049/.051 engines.. partly because I wasn't sure if it would fit between their FRV venturi and cylinder... and if so; whether the outer rubber part would augment the flow into the venturi. There's the possibility of it causing undesirable turbulence.. or even creating a "siphoning" effect. Shocked

The design by nature is minimally-restrictive to exhaust-flow.. unless a really small-orifice header-pipe(s) is used. Even then; there would be considerable "blow-by" where the rubber seals around the cylinder (above and below the cylinder's exhaust-ports). It's designed that way to facilitate installation and removal, by simply pushing-on or pulling-off over the top of the cylinder.

When I started work on the design; I wanted to harness the exhaust for a number of reasons. Noise-reduction yes.. but also to redirect waste-oil.. and hopefully provide a tap for pressurizing an external fuel-tank. The varying-orifice header-pipes were a means to fine-tune any of those three concerns.

I mailed Beta test-kits to a few CEF members.. but nobody got back to me with any data. I haven't done nearly enough testing myself.. and I'm the one that should be doing the most. It's good to re-visit here though. It gets me re-interested.. and my brain-wheels turning.. Laughing

Regarding cylinder-shims; I'm surprised that our two Cox parts-vendors don't list any on their respective websites. I had ordered/received .010" and .015" thickness shims (.049/.051) back in 2018 from EXModel engines.. but I don't see them listed currently. I haven't used the ones I have yet. For me; they were a "good to have if I need them" purchase.

I'll be sure to post any new developments "here".. should any arise.

Thanks again for your interest Yabby. Smile

aspeed Thu Jul 08, 2021 8:41 pm

I thought the .09 head shims worked for the base of the .049s as was mentioned? Haven't checked. They are likely not very thick. If you use a lot of them, then the compression will go away.

roddie Fri Jul 09, 2021 10:29 pm

(deleted by Roddie)

roddie Tue Jan 24, 2023 8:57 pm

Bumping this thread. I want to revisit the muffler design.. and get some more beta test subjects.

roddie Sat Nov 11, 2023 1:20 am

I had sourced some .045" silicone "mat" (cooking item) for cheap.. at my neighborhood Ocean State Job-Lot store. I chose the blue color mat. I made a fence for staple-depth. Consistency is key.

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This is an assembly of two 2" diameter discs.. stapled together and then center-punched .500" The standard "paper-staples" seem to work well. Two layers of this mat equals .090" which "compresses" when being stapled. It's silicone.. and could be the perfect material for this application.

I figured; why not make-up a complete muffler.. so I drilled an inner-chamber out to accept a single header-pipe.

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This header-pipe is completely open. My pipes are spent .22 cal. long-rifle casings. If the primer-end is completely drilled-out, the ID of the casing is .205".

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The aluminum inner-chamber is 1" OD thin-wall tubing; cut to lengths of approx. 5/16". Rings basically. The hole for the pipe is made with a 15/64" drill. Any "tighter".. and it's a real PIA to fit the pipe through from the inside.

I couldn't get the ring in-between the silicone discs dry.. so I used some petroleum jelly which worked really well.

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I also had to add a staple into the circumference.. to tighten the gap where the pipe exits. This was well worth doing and improved the overall sealing of the chamber.

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The silicone will resist temps as high as 450F. which makes this an attractive option for certain applications.

roddie Wed Nov 29, 2023 11:33 pm

Here's a color-change.

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I made a shoe-offset for my stapler.. for an even "band" around the perimeter.

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The punch makes a 7/16" hole in the discs. A 1/2" hole is also fine.. but the idea is to have the rubber "seal-around" the cylinder like a boot; above and below the cylinder's exhaust-ports. This "hole-size" recommendation is exclusively for the Cox .049./051 engine cylinders.

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A #5 drill (.205") will open the casing completely.. for a non-restrictive "open-header" pipe. I drill the inner-ring to accept this pipe; using a 15/64" drill. The casing has a .228" OD.. and is a tight fit. Swapping-out different pipes for altering flow could be a PIA.. but it's better to have the components fit as snug as possible.

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Getting the inner-ring to fit in-between the two silicone discs.. requires lubricant. I used petroleum jelly. It takes strong fingers.

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rsv1cox Thu Nov 30, 2023 7:13 am

So, the baking sheet is resistant to the engines heat and provides a tight fit over the cylinder while the sleeve does the job. I guess you install while the cylinder is off the engine, then screw it back down onto the case?

Why not sew the silicone instead of using staples? So......a needle pulling thread......... la..........etc. etc. Smile

rdw777 Thu Nov 30, 2023 11:34 am

The airplane colors turned out nice Roddie and now a color coordinated muffler, Now that’s pretty cool…. Your muffler design is very innovative…. Great job thinking that one through!!

roddie Fri Dec 01, 2023 12:31 pm

rsv1cox wrote:So, the baking sheet is resistant to the engines heat and provides a tight fit over the cylinder while the sleeve does the job. I guess you install while the cylinder is off the engine, then screw it back down onto the case?

Why not sew the silicone instead of using staples? So......a needle pulling thread......... la..........etc. etc.

Hi Robert, The Silicone material will withstand heat up to 450 degrees F. Punching a slightly smaller hole than the cylinder's OD creates a seal.. all the way around; above and below the exhaust-ports.

Neither the engine's cylinder or glowhead require removal for use on .049/.051 engines. The unit simply pushes-on and pulls-off.

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See below photo; of the 1" dia. aluminum tubing (inner chamber) showing how a dual-pipe set-up will fit around the .049/.051 glowhead.

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The unit will fit the Cox .09 engine cylinders.. but this requires cylinder-removal.

"Sewing" the two silicone discs together is an interesting thought... but the staples are quick and easy. What's more; there needs to be an egress-point for the pipe(s).. which is as simple as leaving a "gap" between staples. They've (staples) stood the test of time.. partly because their inherent oily environment prevents their breakdown from oxidation. Once the inner-chamber (Al. ring) is sandwiched between the silicone discs, it's not generally necessary to remove it ever..
Pipes are installed or swapped-out through either the top or bottom holes of that assembly. As previously mentioned earlier in this thread; there are differing-orifice pipes to experiment with.. as well as a pressure-tap option.

rsv1cox Fri Dec 01, 2023 12:42 pm

It's a work of art roddie, I'm serious. I like it. Got a little Star Wars in it too.

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roddie Sun Dec 03, 2023 12:30 pm

rdw777 wrote:The airplane colors turned out nice Roddie and now a color coordinated muffler, Now that’s pretty cool…. Your muffler design is very innovative…. Great job thinking that one through!!

Thanks Robert! The "red" that I used; ended-up turning-out better than the darker "maroon/burgandy" that was initially planned. The darker red would look more like black.. dk. brown or dk. grey in lower-light views. Still..... I'd like to see how the darker trim looks.

The red silicone material was sourced for exactly that; a color option to the dk. blue. They're both .045" thickness.. which seems to work well from a fabrication standpoint. Thinner material has torn.. and thicker doesn't staple well.. not to mention a LOT heavier.. where unnecessary.

There are considerations/trade-offs which are not uncommon with any innovation. There are clearance-issues with the FRV engines (venturi-restriction) and the fact that any cylinders with SPI will be negatively affected with exhaust-port restriction.

roddie Sun Dec 03, 2023 9:04 pm

rsv1cox wrote:It's a work of art roddie, I'm serious. I like it. Got a little Star Wars in it too.

Robert.. "thank you". My design hasn't had much of a following. I mailed muffler-kits out years ago to a few members here for "beta-testing".. but no one replied with any data. I would have actually appreciated negative-feedback...

I'm going to send "you" a muffler-kit to test-out...... because I know that you love me.. Laughing

and would never want to disappoint me like the others...

rsv1cox Mon Dec 04, 2023 7:05 am

I'll give it a go roddie. Hopefully I will have the parts Space Bug Jr. complete to try it on.

Bob

roddie Fri Dec 15, 2023 11:33 pm

so........ I've sourced a few things that will help with the fabrication process; none of which is mechanized.

The 1" aluminum tubing ring (inner-chamber) is cut to length from a longer tube; by using a plumbing-type pipe-cutter.; which greatly minimizes scrap. The ring needs to be "de-burred" after being cut. I bought a tool that I'm ashamed to admit not having on-hand until now.

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The tool's "hook-blade" will form a chamfer around the edges of the ring. Subsequent light sanding will provide a smooth surface for either the Butyl or Silicone outer-shell to stretch-over.. without chafing on a sharp edge.

Then there's a fractional leather-punch set that I sprung-for to punch holes in the rubber parts.

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It's a better way to do it.. and a cutting mat was included.

then.. I decided to stop in at a local gun dealer to inquire about spent .22 cal. LR casings for making the header-pipes. I'd never visited the store before.. but it turned-out that there was a shooting-range on site. The owner asked me why I wanted the non re-loadable by law casings.. to which I told him about using them for my muffler pipes. He went and brought a pail of brass casings from the range.. and asked me; "how many do you you want?" Shocked

"as many as you can spare"... I said. He put a bunch in a plastic bag for me.. and will give me more if I need them. I thanked him and took my bag of pipes home.