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Speed,Combat,Scale,Racing => Combat => Topic started by: kevin king on January 02, 2022, 03:27:39 AM
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Has anyone ever tried a tongue muffler on a fox 36? I really dont want people that launch the plane to go deaf myself included.
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Kevin,
A lot of the combat crowd has some level of hearing impairment . Ear plugs and muffs should be part all combat flyers and pitmens tool kit .
Mufflers are a P.I.T.A. for Fox engines unless you have landing gear . The loudest engine I ever pitted was a Cippolla .36 rear exhaust. It literally hurt .
Get over to Princess Auto and pick up some hearing protection. Even with tongue mufflers a Fox .36 will be too loud for long exposure.
Brad
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Thanks Brad.
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A while back I experimented with a Tongue muffler laid parallel with the Cylinder head using a home made 90 deg. adapter. Worked OK but did not reduce the noise to any great extent. Roy Glen saw what I was doing and sent me his version. A tube muffler with an inner drilled tube drilled with many holes and an outer tube for mounting. Much quieter than my version but much harder to fabricate.
Did not continue any further development.
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Tongue mufflers are good for compliance with muffler rules and getting the exhaust outside the cowl.
If you really want to reduce the painful jolt of energy when the exhaust port first opens, you need an expansion chamber with some amount of volume.
A contraption with a lot of holes and no volume just channels the noise straight through.
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A tube muffler with an inner drilled tube drilled with many holes and an outer tube for mounting.
That sounds like a typical motorcycle canister muffler. I wonder if the guy's muffler could have fiberglass packing for more sound suppression (think Kerker cans from the 80s-90s).
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Per a technical journal I read back when combat mufflers were is discussion, to paraphrase:
A muffler with NO back pressure allows the ear-splitting noise to go right through.
The engine only makes BAD noise about 2% of the time. The ultimate muffler opening is open 100% of the time. The expansion chamber converts the series of ear-damaging impacts into a steady flow of less harmful noise.
The ultimate muffler opening only needs to be 20-25% the size of the initial exhaust port to reduce noise without loss of power.
Noisy exhaust systems are an expression of machismo without added performance.
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It will be hard to look macho with hearing aids.😁
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Noisy exhaust systems are an expression of machismo without added performance.
So that's why Harley riders and crotch-rocket guys do that, eh? ;D
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So that's why Harley riders and crotch-rocket guys do that, eh? ;D
Only the dumb ones! . . . . . . . the smart ones fit turbo's! Best silencer that adds power too! #^
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It will be hard to look macho with hearing aids.😁
The guys with loud mufflers are already deaf. Now they're out to blow out YOUR ears.
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I try to use hearing protection as much as possible. I use either foam ear plugs 33db or Peltor earmuffs. I use earing protection for work and always look for 30plus db noise reduction.
To answer your question. We have put tongue mufflers on our 36x's with no ill effects except maybe some power loss. We only did this to comply with a muffler requirement at our R/C field. A club member made them for us. Very little noise reduction but that was more to just comply
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All the Schneurle type engines use ports, some with as many as 8 ports in the sleeve- at least two exhaust ports and anywhere from 3-6 bypass ports. All of them use various rounded and "faired" angles on the ports.
There are NO rectangular or square port shapes.
All the older engines, circa 1955- 1960's had simple rectangular ports with sharp square corners. Most had only 2-3 ports, 1 or 2 exhaust and 1 or 2 by pass ports.
I'm sure all the old timers will agree that the older engines had a lot more "bark" in the exhaust noise.
The later Schneurle style engines and much fewer sharp overtones despite putting out 2-3 times as much horsepower or more.
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Tongue mufflers are kind of useless.
A double wall tube muffler with a couple of baffles and an exhaust "pipe" can be sized to make a quite effective muffler. The most recent K&B engines, from Mecoa.com have fairly light tubular mufflers that work quite well.
The OS mufflers are similar design and weight and work just as well.
Several other companies (home jobs) make similar, lighter versions.
For most combat types the muffler should be made or modified to fit close to the engine cylinder to prevent "landing" damage.
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If you haven't used a db meter to measure, you might not realize the difference. A drop of 3 db on the meter cuts the sound pressure in half. Your ears can only detect a drop of 10db or more. Do to an issue at the park where we fly regarding birds, we were forced to do a lot of sound measurements on combat planes. A modern F2d engine turning 30K is below 86db at 10 meters and below 90 within a foot or two. The background noise from the freeway at the flying field is 86+db even with light traffic. We tried to measure the combined sound pressure from two F2D's flying a match but the sound 20 ft outside the circle was below the "background" level of 86db. A lot of the noise on our engines comes from the propeller and the intake. Ever heard a 1/2A electric pylon racer? they are almost silent without a propeller, but with a 4 1/2" prop turning 40,000 RPM they are louder than a Cyclon .049. If you're launching loud airplanes it's always a good idea to wear ear protection. A normal conversation is in the 60db range and above 85db causes hearing loss according to OSHA.
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The sound meter I use gives a graph of the whole cycle. The damaging and problem-causing part of the cycle is right when the exhaust port opens, which is only a few degrees.
A slow-reading meter will record only the average and not the harmful pulse.
An F2d expansion camber will allow this pulse to average-down before it escapes into the environment. A wide open exhaust will hurt your ears like a B-25 it's thirty-six open pipes.
Any muffler is better than nothing, unless the ultimate constriction is same size as the engine exhuast opening.