Why aren't there quieter IC engines? - RC Groups
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Oct 12, 2001, 08:13 AM
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chlee's Avatar

Why aren't there quieter IC engines?

Hi all,

I was wondering, with all the pressures on glow flying fields and the high cost of electrics, why aren't there more super-quiet engines out there? If you could quiet down a glow engine to the 70 dB range, that would solve a lot of problems.

The first obvious problem has to do with the bulkiness of mufflers. But you could increase the weight of mufflers quite a bit and still have a higher thrust to weight ratio than most electrics. The problem may lie in the fact that a muffler can't be easily hidden away inside the fuse; with its exhaust and all, placement of a very large muffler would have to be an integral part of the plane's design.

I've a Norvel .061, and just for kicks, I'm thinking about constructing a huge muffler out of 3 coke can halves nested inside each other. (I've done this for a .40 engine, and it reduces the noise to something comparable to a blender or garbage disposal. It did not overheat the engine.) Then I'll have to design an entire plane to go around this ridiculously bulky contraption.

Anyway, it will be interesting to see whether one could really quiet down a glow engine and still retain a performance advantage (thrust/weight) at the end of the day.

Tell me what y'all think,
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Oct 12, 2001, 09:06 AM
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dunno.. sounds like a good question for RCGroups.com
Oct 12, 2001, 09:09 AM
AMA 697691 / FAA 13675
Try a 4-stroke. They are very quiet and oh so powerful!
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Oct 12, 2001, 09:33 AM
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Bill Glover's Avatar
70 dB is incredibly quiet, I suspect many electrics would be over that. My club had a glider & electric site where ICs below 78 dB (at 7 metres) could also fly, 2-strokes up to about .35-.40 size could achieve this with careful silencing & prop selection.

I have some very quiet IC models, one has an OS 10FSR with a baffled .40 size extension silencer - that is probably quieter than my Pico Jet!

The problem with noise is that it's subjective, my Webra T4-80 4 stroke is actually over my club's 82 dB limit ... but nobody has ever queried it because it doesn't sound loud. At the other end of the scale, I was asked to stop flying TD 010 and 020 powered r/c models (which barely registered on the DB meter)!

Engine manufacturers are slowly responding to the demand to produce quieter 2-strokes, standard silencers are much better than they used to be and motors like the 'Q' series from Irvine are pretty good (very good if you add the optional 'mouse' extension silencer).

Back to your specific project, a few years back a number of people in the UK were using 'beer can' silencers built in to the fus. - with motors up to about .10 size the majority of the noise left was from the prop! Induction noise also starts to become significant, if you look at current 2-stroke IC pattern planes most of them try to mask the air intake (and of course use rubber mounts to stop vibration being transmitted through the airframe).

Even with rubber mounts, the type of covering you use affects how noisy the model is if it's an 'open frame' type. I have a fun-fly (piped Irvine 36, 11x4, Parc-Amber resilient mounts) that resonates quite badly due to the Fibafilm covering.
Oct 12, 2001, 10:36 AM
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Don Sims's Avatar
Are they running an "Exhaust pipe" from the engine into the fuse to the muffler built inside the fuse? How would this effect the CG?
Oct 12, 2001, 10:57 AM
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Don, You've got it just right - the simplest form of fus silencer would have a pipe leading into a balsa box coated with epoxy.

I have to agree with Bill on everything that he says - I was just thinking that I have a Precedent Fun Fly that takes off at a little over 4.5lb, and the performance is good with it's OS FP40, 11x6 APC, and OS silencer extension kit (with only the rear baffle). I stopped flying it because with ANY other IC model flying I couldn't hear the engine.

Regards, John
Oct 12, 2001, 11:02 AM
Build'em and Crash'em
Ken Lapointe's Avatar
There are very quiet IC sytsems out there. One of the guys in my club has a 4 stroke pattern plane that is just as quiet as my electric.

Oct 12, 2001, 11:13 AM
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Bill Glover's Avatar
Don, if you mean the beer-can silencers ... they weigh virtually nothing, so no real impact on the CG. Of course you need to plan the tank & r/c installation around it though!

The models I saw had fairly deep fuselages with the motors angled over so the stock silencer pointed back at the firewall. Then just a short length of pipe from the tailpipe, through the firewall, and into the beer can. The can had a short pipe at the back, exiting vertically down through the fus. floor.
Oct 12, 2001, 06:22 PM
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Don Sims's Avatar
Thanks for the info. Do you think that this may have been a fad? Also it seems to me that there is a lot of waste liquids when you fly IC planes and that would make a dangerous combination if it's flamable in a Balsa style muffler and that it would accumalate in the beer cans. Now, I'm all for emptying the cans when they build them!
Oct 14, 2001, 03:51 PM
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Bill Glover's Avatar
Yes, emptying the beer can is a vital part of the job, you certainly don't want to waste the contents!

What comes out of the exhaust port is not flammable, just castor oil (or synthetic, depending on what you use) plus water vapour. Any kind of baffled silencer can potentially get buildup of liquid, but generally there are enough routes for it to drain out. With the beer can silencers it's not a problem as they contain no baffles ... the oil etc. comes out via the downward pointing exhaust pipe.

I use 'quiet pipes' on virtually all my 2-stroke models, with these it's essential to hang the model tail down (if you hang it up for storage). Nose down and the water/oil mix in the pipe drains back into the cylinder ... not a good idea. Ordinary silencers are less prone to this as the gunk collects in the nose part of the silencer, but there are other good reasons for hanging tail down e.g. any fluid in the crankcase drains onto the backplate rather than laying on the bearings, and any fuel dregs in the tank sit at the back of the tank rather than the bung at the front (which over a long period will deteriorate).

I make a 'crud catcher' for each model .. this is a short length of silicone tube that goes onto the exhaust tailpipe, with an aerosol lid attached to catch the oil & water that drains out of the pipe while the model is hanging up.

The 'epoxy coated balsa box' style of internal silencer has never appealed to me, but do I know it's been used successfully.
Oct 14, 2001, 09:54 PM
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Don Sims's Avatar
I really don't consider electrics to be all that high a cost especially if you build your own battery packs. There is an excellent discussion of this in the open forum if you haven't read it yet:


I was into RC back in the 70's and after a 25+ year hiatis, I'm back in. Electric is the most convienyant for me and I enjoy the challenge of it. I consider myself a rookie still and have a lot to learn!! But, I'm having a blast learning!

Bill, I really appreciate your comments and ideas, If I get back into IC they will be a big help!!
Last edited by Don Sims; Oct 14, 2001 at 09:58 PM.
Oct 14, 2001, 10:39 PM
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I fly in two large clubs in the Sacramento area.

Electric flyers are very few, I'm usually the only one. I fly mainly AF cobalts, which are competetive with a lot of the IC planes ( except in duration). The big problem with noisy planes that I have seen is that the guys LIKE the noise!!

Noise somehow equates to speed and power.
Even though the pattern planes, which will out perform any sport plane and most racers, make almost to noise at all.

???????? Another facet of life I don't understand.

Oct 15, 2001, 02:58 AM
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Don Sims's Avatar
Hey Dave W. Thanks for dropping by and posting!!
Oct 31, 2001, 01:26 AM
iankraus's Avatar
there is a company called fly quiet that makes after mufflers if you feel to lazy to make your own.
I haven't tried them but the product seems cool.

I love the quiet powerful sound of my
rossi .45's mini pipe / muffler!!

My geared spd 400 models can make some noise.

Nov 26, 2001, 08:06 PM
Registered User
Hi guys
I fly only electric(and am new at rc) but I am a pretty decent two-stroke mechanic. I'm poking in to tell you guys about a book called "Two Stroke Performance Tuning" by A. Graham Bell it is about motorcyles but he has a verrry goood section on expansion chambers and how to silence them good stuff!
By the way the sound is very important and oh that smell!