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"Black Lynx .049 with a Throttle, Exhaust Deflector and Nelson-Galbreath head set"



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a cheap sport muffler

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Re: a cheap sport muffler

Post  roddie on 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.
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Re: a cheap sport muffler

Post  roddie on 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.
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Re: a cheap sport muffler

Post  KariFS on 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.

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Re: a cheap sport muffler

Post  roddie on 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...

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SPI testing..

Post  roddie on 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
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Re: a cheap sport muffler

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