Author Topic: Tuned muffler (Read 2029 times)

Gary Dowler · « **on:** August 21, 2018, 03:10:17 PM »

So typically how much benefit is there to having a tuned muffler as opposed to a factory expansion muffler?
I'm referring mainly to my OS 20FP at the moment.

Gary

Steve Helmick · « **Reply #1 on:** August 23, 2018, 09:21:25 AM »

Quote from: Gary Dowler on August 21, 2018, 03:10:17 PM

So typically how much benefit is there to having a tuned muffler as opposed to a factory expansion muffler?
I'm referring mainly to my OS 20FP at the moment.

Gary

I suspect that folks are wondering what you mean by a "tuned muffler". And maybe that the last .20FP "factory expansion muffler" (same as the one with the .25LA) is apparently a tuned muffler. The one thing that puzzles me about that muffler is that it doesn't seem to do anything good for a .25FP, which always seems to suffer the runaways.

By "tuned muffler", I have to guess that you mean "tuned pipe", like most (not all) folks run on the .40-.46VF, RO-Jett and PA engines. The reason is to regulate the power through the maneuvers, adding here and reducing there, usually referred to as "boost" and "braking". Dirty Dan (last we saw him around here) was flying a .25FP with a muffled tuned pipe selected from the MACS catalog, but since they went away, that's not very useful info. I believe Randy Aero sells a small CF pipe that might work, in the Benjamin price range. Meanwhile, the *good* .20FP muffler does that well enough.

Steve

Lauri Malila · « **Reply #2 on:** August 23, 2018, 09:54:35 AM »

Gary,

My muffler is tuned. Powerwise it's about neutral, but chambers (2 normal expansion and 1 side resonance chamber) are tuned to filter away the most annoying frequencies.
Finding the right combination of chamber volumes is easier said than done, first because the formulaes are based on static gas, and secondly because the spectrum coming out from a typical stunt engines exhaust is difficult to handle.
Steve, If an engine suffers from runaways, my first suspect is not the muffler. It's a power management issue.

Lauri

Gary Dowler · « **Reply #3 on:** August 23, 2018, 10:56:31 AM »

https://m.ebay.com/itm/MAC-Tuned-Muffler-for-OS-20-25-FP-LA-Magnum-21-28-TT-GP-25-Rare/142907082965?hash=item2145ed08d5:g:hUcAAOSwftZbdOiy
Here is what I was looking at. The muffler I have now is the stock one ZoS shipped them all with.

Gary

Fredvon4 · « **Reply #4 on:** August 23, 2018, 12:39:01 PM »

Gary the answer to you question has a lot to do with how you want to run the OS FP 20...

For stunt I think the BBTU using a stock unmolested engine with the supplied E-2030 muffler acts like a tuned pipe but only on that engine..on a LA or FP 25 it does not do the same regulation

Any True Tuned pipe optimized for the FP 20 would usually be configured as a Power adder for speed, racing, combat, cars, or boats

That fixed length "tuned" pipe on E-bay may or may not be set to "Just the right length" because it is from MACs we can assume it is a good pipe...but for what application ...I don't know

That said if you have the FP 20 and the E-2030 muff and intend to set up on a 35 sized stunt plane you probably gain nothing with the MACs black pipe...IMO

Gary Dowler · « **Reply #5 on:** August 23, 2018, 01:01:40 PM »

Good enough, that's what I was trying to figure out.

Thanks

Gary

Brett Buck · « **Reply #6 on:** August 23, 2018, 01:13:14 PM »

Quote from: Gary Dowler on August 21, 2018, 03:10:17 PM

So typically how much benefit is there to having a tuned muffler as opposed to a factory expansion muffler?
I'm referring mainly to my OS 20FP at the moment.

I haven't tried the particular muffler to which you refer, so only one way to find out. My strong suspicion is that this one is probably intended to operate at a higher RPM than you want.

It's entirely luck that the E2030 works the way it does for us, as far as I can tell. It works better on the 20 than the 25, because the 25 has enough power that even though the (weak) regulating effect at the desired RPM still happens, it has enough to push past the "valley", at which point it speeds up to the next "hill".

The 20 will easily "run away" with a tongue muffler or open exhaust. "Run away" is a misnomer, of course, it's running as it is intended to run. The fact that we want it to run far less power than it is capable to get the speed right is an oddity, as is the fact that the tuning happens to hold it at a desirable RPM for our purposes with a 4" pitch prop.

Brett

Gary Dowler · « **Reply #7 on:** August 23, 2018, 03:49:41 PM »

Thanks Brett. I had seen mentions at times about tuned pipes, etc, then the other day on eBay I saw that "tuned muffler" and was curious about it.
I was beginning to think I wasn't going to hear from anyone.
Sounds like the 2030 muffler is all that's needed.

Gary

Brett Buck · « **Reply #8 on:** August 23, 2018, 04:24:32 PM »

Quote from: Gary Dowler on August 23, 2018, 03:49:41 PM

Thanks Brett. I had seen mentions at times about tuned pipes, etc, then the other day on eBay I saw that "tuned muffler" and was curious about it.
I was beginning to think I wasn't going to hear from anyone.
Sounds like the 2030 muffler is all that's needed.

It ran a hell of a lot better with that one, than anything else I tried. And, it's pretty quiet, much less noise than a typical 4-stroke, for instance.

Brett

Steve Helmick · « **Reply #9 on:** August 23, 2018, 05:27:28 PM »

Well now. It happens that there has been some R&D done with the MACS Muffler for stunt use here in the PNW, by Scott Riese, in PDX. Also flown a bunch by Nils Norling over in the Madras area, on a Profile Oriental. By all accounts, it works really well on a STOCK .40FP. I ran it myself on a stock .46LA, but it did require a different propeller. I liked the run, the fuel economy, and that muffler makes a wonderful handle for carrying your plane to/from the circle. Well, you do want to let it cool off a bit after a flight. It's a bit ugly to some. I had it on a Humongus, which isn't beautiful.

The only bad thing about it is that you have to search for THE propeller that gives you a launch rpm right about 10.2k for the .40/.46 size MACS Muffler. And of course, makes your airplane "happy". Basically, fiddling with props, line length and therefore tip weight to find joy. The engine still needs to be rich enough that it doesn't sag lean in the later (higher) part of the pattern. The bad thing is that the tuned length is fixed, so you're tied to that rpm. With the CF stunt pipes being adjustable, I think that actually would make things easier or at least way better when you eventually get it sorted.

It happens that I have a NIP MACS Muffler for a Magnum XL .25/.28, and I think it might also bolt onto an XLS .36. I'm not at all confident that it would bolt to a .20/.25FP or LA .25. I can tell you that they typically interfere with the LG leg on a side-mounted engine on a typical tail-dragger LG. Great on a trike or monowheel! On an upright or inverted engine, they usually interfere with that wing thing. I have always wondered if the .25 sized MACS Muffler would require a higher launch rpm, or if ol' Mac always made all of his mufflers to launch at 10.2k (or real close, maybe +/- 200 r's).

I've never owned an OS .20FP or .25FP, but I have seen a lot of folks have "run away" problems with the .25FP, and some were Expert class fliers. Not having ever had one or messed with somebody else's, I always figured that there should be a fuel/prop combination that would make the .25FP run steady...more oil, less pitch, maybe.

Some have said the .25FP cylinder liner is too thin and makes them unstable. Yet, the .46LA cylinder is very thin, and they're very nice. Not to mention the Fox .35 Stunt, which also has very thin cylinder walls, and...well, never mind. Maybe somebody would take apart their .25FP and .25LA and tell us what is different?

Steve

Brett Buck · « **Reply #10 on:** August 23, 2018, 05:38:06 PM »

Quote from: Steve Helmick on August 23, 2018, 05:27:28 PM

I've never owned an OS .20FP or .25FP, but I have seen a lot of folks have "run away" problems with the .25FP, and some were Expert class fliers. Not having ever had one or messed with somebody else's, I always figured that there should be a fuel/prop combination that would make the .25FP run steady...more oil, less pitch, maybe.

Some have said the .25FP cylinder liner is too thin and makes them unstable. Yet, the .46LA cylinder is very thin, and they're very nice. Not to mention the Fox .35 Stunt, which also has very thin cylinder walls, and...well, never mind. Maybe somebody would take apart their .25FP and .25LA and tell us what is different?

I think we explained it about 30 years ago, it's the tuning working against you rather than for you like it does on the 20. Same thing happens if you put your pipe too short, it can jump to the next node, if you have enough power in the "valley" to get past it.

The liner has nothing to do with it, but I would note that the Fox liner is thin, but it's steel, rather than aluminum, and so much more rigid for a given thickness

We know the difference between the 25FP and 25LA - the FP has a boost port and the LA does not - neatly solving the high-speed breathing issue for us, and adding a bit of slope to the HP curve at the RPM the muffler tuning works, preventing it from jumping beyond the "valley".

Brett

Author Topic: Tuned muffler (Read 2029 times)

Gary Dowler

Tuned muffler

Steve Helmick

Re: Tuned muffler

Lauri Malila

Re: Tuned muffler

Gary Dowler

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Fredvon4

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Gary Dowler

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Brett Buck

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Gary Dowler

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Brett Buck

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Steve Helmick

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Brett Buck

Re: Tuned muffler