What noise annoys an oyster?

I was flying my Nobler yesterday, Brodak 40 + muffler that comes with it. Without a doubt it is NOISY. Now, why should our tiny little motors be more noisy than a motor car of hugely greater engine capacity and power output? Answer - the silencing system.

It is possible to dramatically reduce the noise output of our IC engines - why don't we do it? Weight? Yes that can be a factor. Power loss? That too can be a worry. But a properly designed system can be light and need not compromise power severely.

What I intend to do is use two home-made mufflers in series. I make them out of thin-walled scent spray cans and the weight is minimal. My guess is that with two in series the noise output should be pretty low. A bit finicky to sort it out initially, but I am sure it will work.

This is extremely relevant to the future of our hobby. I remember the furore when silencers first became mandatory - but we have now not moved forward in over 20 years - but the world has. IF our motors were really quiet we would not have noise issues, and noise seems to be one of, if not the most inhibiting factor.

I believe that we can make IC engines almost as quiet as electric - if we put our minds to it. Then we could fly on football fields etc. and apart from keeping idiots out of the circle I think there would be no problems. Of course this "silent treatment" can apply to Combat also.

Charles

I've made several mufflers over the years. The best I came up with was a simple Aluminium Tube. I covered up the front end, and cover up the back end, and drilled enough 1/8" dia holes in the back end to equal the engine exhaust area. Not very scientific, but cheap, effective and light, about 1.5 oz. I used a steel strap to hold it on, and tapped 4-40 threads in the strap. The total weight about 1.75 oz. Scott Dingers mufflers are slightly lighter, but the same principle.
The problem is alway going to be the frequency of the sound. Our engines "stand out" from background noise because of frequency. I have tried adjusting the exhaust timing to lower the rpm where good power is attained. This helps, but you can't beat a 4 cycle for lower frequency.
All this being said, the local field has a "no liquid fuel" restriction. Electrics and gliders only. Doesn't matter how quiet your gas plane is. I think we are going to find that the city fathers will always take the easy way out and ban gas engines, or just ban model airplanes entirely. They have little sympathy for oldsters playing with toys. And they don't even much care about youngsters who don't vote.

You will soon get to the point whewre the prop noise is greater than the engine noise. This is the current problem (no pun) with electrics.

Curt

Hi

That was part of the aim of my title - the noise of our motors can be "annoying" To me the most horrible noise is the tinny two-stroke motorcycle of about 50cc capacity.

What I do not know is whether it helps to wrap the muffler in some sort of sound-absorbent material, say about 1/8" thick. If I'm not rushing all around the world this summer I'd like to have a go at producing a really quiet system. Does anyone have any theory or physics on this? Mine is just High School physics from about 50 years ago.

On larger systems I know that feeding the exhaust of a diesel generator into a drum buried in the ground made them very quiet indeed.

Charles

Curt-

The last time the Canadian contingent came down to Cleveland for our Stunt Championships, they had two really quiet set-ups. Do you know anything about their techniques?

Konstantin's I.C. setup was so quiet that the prop noise seemed to be the greatest contribution, and we could easily hear the flight lines' whine as they whipped through maneuvers downwind. I believe these sound levels were near those of electric units - pretty impressive!

SK

No I don't Serge.

I recall Konstantine was using his own mfg engine--but I'm sure it was a 2 stroke.

Peter Hansn has been here and his 4 stroke is very quite.

In 4 s it can depend alot upon the valve timing overlap.

The two strokes must also depend upon the port timing to some degree I would think. The discovery retro's are very quiet.

Props vary all over the place and can depend upon diameter, RPM, tip shape, etc.

So...no I don't know.

Curt

I think you will also get to the point where you will find some people have nothing better to do than complain about anything. I was talking to a park ranger about complaints he had received from residents living near a park where RC is flown. He said one time he received several noise complaints in an afternoon regarding RC fliers. When he investigated, the RCers were flying gliders. NOT power assist gliders, hand (discus?) launched gliders. I think the noise issue is a lot of times just an excuse. Some people just can't stand to see other people enjoying themselves.

cheers,
Ken

Charles,
I fly a Brodak 40 in a Jamison for Old Time Stunt and am surprised to hear that you seem to think it's noisy. Mine seems to be quieter than most engines at our flying field. In fact quieter than just about anything else except the electrics.
My setup uses the stock muffler with a rubber extension tube (which does seem to dampen the resonance from the outside of the muffler) and a 10.5 X 5 APC prop.

Also remember that props contribute significantly to the noise level. Some are more noisy than others.

Mufflers can certainly make the exhaust note quieter but won't do anything for airframe resonances etc.

Randy - I'm using the same prop as you. I've got some 3/8" ID silicone tubing that I'll try on the outlet

Charles

Charles,
Yes, wrapping the muffler can reduce resonances and therefore reduce noise. However wrapping the muffler will also create more heat in the exhaust system. This could have good or bad effects on the way the engine runs but most likely will effect it's run qualities.
As far as physics are concerned this is a very complex problem involving resonances of the airframe (motor mounts, wing, and fuselage), which can easily amplify the sound (noise), Propellor, etc.

The FAI Pattern guys use special props, rubber mounts, and very careful construction to aid in reducing noise to meet the sound level requirements. Of course they use much larger engines and props than we do.

Make your mufflers and let us know how it works out, however I would strongly suggest trying some simple damping measures with foam rubber in the tank compartment, and a rubber extension on the muffler before proceeding.

Not to really get into that discussion, but noise is usually an excuse for closing down CL flying fields not a reason.

I tried building a muffler a few years ago. A really quite one. Actually worked pretty well. I got a chunk of thin walled, 1" aluminum tubing and a second piece that was about 13/16" diameter. I drilled about 50 5/32" holes all along the length of the smaller diameter tube. The I wraped it with "0000" steel wool and inserted that into the larger tube. Then I machined an end plug with inlet to fit a rear exhaust engine I was working with (a Stalker). I used a silicon coupler to attach the thing. The other end got another machined plug with a hole in the middle. An exhaust stinger that ran the length of the muffler, running through the hole in the end plug, had a bunch of holes punched in it all along the length and was capped on the forward end. The stinger had a bend in it to dump out the bottom of the plane.

It was unbeliveable how quite the system was and I didn't detect much in the way of power loss. The whole thing weighed about 1.75oz and seemed to work really well overall. But the big difference was the "pitch" of the exhaust note. It really took away that piercing sound. It sounded more like a two stroke lawn mower.

Ah! Now that sounds like a great idea.

Do you a photo or drawing? I'd be really interested to see it.

Charles

Ok, could someone please explain to me what an 'exhaust stinger' is?

Sounds like some sort of inner tube which runs from the outlet of the muffler, towards the front?

Colin,
Looks like your question has been ignored. Sorry.
The "Stinger" we're talking about is a molded silicon rubber fitting that goes on the end of a muffler or tuned pipe. It's primary purpose is to deflect the exhaust gases down away from the wing or actually out of the fuselage and down in the case of a tuned pipe. They are available is several sizes, since they are rubber they can add some accoustic damping effect to the muffler or pipe. They are fastened to the muffler or pipe with a simple tie wrap. They should be available from any descent hobby shop or certainly from Aero Products, RSM, Tower, Etc.

Charles,

Sorry, I don't have it any more...or the engine. Sigh... I had two Stalker 61RE engines. Sold one and splatted the other.

K&B built some very effective mufflers for their Sportster series of engines. These were true multi chambered mufflers with internal baffles much the same as car mufflers. The loss of power on the .28 was substantial, but it did silence the engine down to very effectively.

The R/C pattern guys did a lot of research in this field because of the very strong rules noise rules in Europe. It lead to two major developments, one the 4-cycle model airplane engine. Second the development of very effective muffled tuned pipe exhaust systems for 2-cycle engines.

One thing about engine noise is the confusion between sound pressure levels that are measured with db meters and the perceived noise levels that often lead to complaints. My Zenoah 62cc gas engine produces far greater sound pressure level measurements than my old K&B 6.6cc (40) engine using a stinger pipe (non-muffled). But the Zenoah ran in the area of 8K RPB on a 22x10 prop. Where as, the K&B 6.6cc engine unloaded with a 9x5 prop turned in area of 20K+ RPM (on the ground it was set to 18.5K). The rather low frequency of the exhaust note and the low frequency prop noise gave the Zenoah a low frequency Omni directional noise signature that most people do not find offensive. Much the same as a gas powered weed eater, noisy if you are next to it but not really noticeable if you are a couple of blocks away. Where as, the 20K frequency of the 6.5cc engine was very directional and very irritable at quite a distance if the noise was coming in your directions. Which also produces a second side effect the noise comes in and out depending on the direction of the plane is pointed. Kind of like a siren wailing, it gets peoples attention.

One last thing, as I said above what we call mufflers are in reality an expansion chamber designed to build a small amount of back pressure to tone down the engines noise level without taking away too much power. One answer is to use larger displacement engines with real effective mufflers, using large props running lower RPM range. Which I might add is kind of the engine we in control line are looking for. Unfortunately that is not the kind of power the R/C guys are looking for and they are the 800 pound gorilla.

That Stalker sounded like a Harley.

Howard Rush

Howard,

That was with the stock muffler with the baffles pulled. Even at that it wasn't all that loud or irritating. Unlike piped engines that sound like a high pitched, angry beehive.

edit for typo

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Ah, the old reliable steel wool trick! VERY effective. When just a lad, I had a '48 Cad with very loud dual exhaust, and was cited by a city policeman. I stuffed some steel wool up the tailpipes, drilled some holes, and held the steel wool in there with nails. When I took the car to the station, that policeman stood behind the Caddy and had me rev it up. When I let 'er rip, the steel wool blew out, fragments of it ricocheting off his shiny black boots. He was less-than-amused, and the Caddy got a new set of Glasspacks!

The OS LA mufflers are very effective. Combine the baffle with Randy's ideas for a double wall sound chamber and it could get a lot better.

Last year at Brodak's somebody put an electric setup in a Brodak P-40. He used the AXI2810 motor and a stock wooden prop(not sure which one). The plane flew fine, but it was at least as noisy as all the LA's using stock mufflers. All prop noise.

As pointed out by others, RPM is a big factor. Anything over about 9000 starts to get irritating. I was flying with the Piston Poppers in Minneapolis one summer, when they had the field with the sound demon neighbor. An LA 25 on an 8/4 APC prop turning about 16,000 rpm measured well within their range, something like 90 db at 9 ft and 74 db max in the air. But it was definitely a "noisier" sound, even though the measurements showed it to be adequately quiet. So if you are really trying to be quiet you need both rpm and tip speed limits.

Charles,

A couple years ago I made a rear exhaust muffler using a mouse can and some thin wall aluminum tubing. I posted the construction on the Barton site:

http://controlline.org.uk/phpBB2/viewtopic.php?t=380&highlight=

Sorry, I haven't done a sound level check.

Fred

You should check with the Yatsenko borthers before you even start. They have the lead on quiet technology with IC engines. Getting any info from them should be helpful and save time and help in your direction.

Fred,

That's looking good. Your can is about the same as my scent (or soldering iron gas) container. I use the same sort of system but with a straight-through pipe blocked in the middle, so the exhaust goes into the can, then from the can out the tailpipe. The one I use on my TT-42 and the RC Nobler seems to work well.

I am sure with proper design (and maybe the right porting on the motor) we can have quietness and power. Most car and motorcycle motors lose a huge amount of power if run with an open pipe type exhaust system I think.

I am DETERMINED to get a QUIET and powerful motor run, if humanly possible

Charles

Charles,

I suspect that not everyone noticed that you are in the UK... Sound standards on the Isles and the Continent are much more stringent than here. Another annoyance is the Doppler effect on the sound, mentioned in regard to a 20kRPM K&B in the thread. The rising and falling sound can annoy the uninformed.

In the USA, tolerance of sound varies with different regions. Here in southern Arizona we are fortunate in that we have a fine site far enough from neighbors that mufflers are optional. In fact, a gent from the UK (Tom Jolley?) had a large 'double Monitor' at a VSC several years ago. The engine was a large sparker, Atwood Triumph or Anderson Spitfire.

It was loud.

I was on the other circle at the time, trying to hear my PAW 19BR (in a Sterling Rngmaster.)

On the other hand, Rene' Berger, occasional Swiss F2B Champion, spends part of winters here with us. His VECO Squaw is nearly silent - at least by comparison. The stock OS LA series mufflers are quite good, by colonial standards. The Brodak 40 stock muffler does not seem excessively loud, by our standards, but you face a different problem.

The steel wool packed tube muffler may damp the loudness enough, but keep in mind necessary maintenance! The mesh can load up with exhaust oils and 1) grow in weight in a short time, and 2) the oil loading up in the mesh may restrict flow, increasing heat and costing power.

Luck!

Someone mentioned "Scott Dingers mufflers". What are they and where can they be purchased?

Guy Blankinship

Look for sq8s in the Profiles listing of this forum.

Howard Rush

>Someone mentioned "Scott Dingers mufflers". What
>are they and where can they be purchased?
>
>Guy Blankinship

Check the "Links" page on the DMAA website

http://www.DMAA-1902.org/

Bill Lee

Scott Dinger
[email protected]

Greg L. Bahrman

According to RC fliers, you can actually get a performance INCREASE with mousse can mufflers:

http://webpages.charter.net/rcfu/ConstGuide/MCM.html



There are also integral ones, where you glue the mousse can to the front part of an existing muffler:

http://www.spadtothebone.com/SPAD/Mufflers/

[photo not recovered: Norvel10.jpg]

noise comes mainly from exaust, INTAKE and proptips/speed and airframes(drum tight plastic covering--hollow balsa/ridged structures

intake noise on 2 strokes is loud--ask anyone(or me) who raced mac powered go karts with out airfilters(still noisy with airfilters)expesily 91s and 101s with the huge fule injector carbs.

lots of ways on exaust and intake
one method is dead end tubes leading off of main duct/pipe
very efective

open the hood of most new cars and look at intake system piping/ducting
and you will find small chambers/pipe leading off of main duct.
this greatly reduce noise at road speed rpms.
have seen this on dirtbikes and 4wheelers also

works on exaust as well
can be tuned to deliver more power on intake and exaust also

books a million---scientific tuning of intake and exaust systems covers the subject at a very deep level--deeper than i can go!
lots of math!

prop tip shape and reducing tip speeds help.

ear plugs are the answer--they hand them out at jobsites for free
tell the complainers that they are part of wellfare program and watch how fast they go get them!--when they find out they cant hear the boom boxes as loud as before they might get depressed then they can get free mood stabilizing drug and the world will be at peace.

me-i like da noise!
forth of july has been canceled due to noise
i like da noise!

stunt is more pleasing with a purring as opposed to screamin engine

David
where engines make noise or the must be broke

I believe i've found what you are looking for:

http://www.flyquiet.com/

Interesting! Anyone here used one of these?

Hi Charles

Interesting, and pertinant, issue. Two-strokes are quite complex and if you get the nuffler right you can quieten things down and add to the power. Just Engines in the UK have several ranges of mufflers, including 'standard', 'quiet' and tuned pipes. You might visit their site: http://www.justengines.unseen.org/.

There is a municipal cricket field within walking distance of my home, which is used only occasionaly for cricket, and I flew my Nobler + Brodak 40 with muffler there once. Within about 3 miliseconds there was a group of digruntled neighbours acting in an unfriendly way. So I built a Brodak Smoothie and fitted it out with an electric set-up. It flies like a dream and I now have a bunch of kids, of all ages, building electric Flight Streaks as trainers. So far no objections to the noise. The biggest problem is the long time it takes to re-charge the LiPo batteries. I have bought a few of them, expensive, but now get in a lot of flying and save the costs of driving 20km to the regular club, which is also under threat now due to urban creep.

Richard Becker
Stunted

Maybe you should take a few flights with an unmuffled FAST Combat job, then, when they yelp, offer to downgrade to a muffled Brodak 40.

They'll go home brag about winning the confrontation. It's about "making a difference".

If you lead off with a 'lectro-toy, they'll lead off with "safety".

Thanks all, some really interesting replies.

If I could hear the noise of the lines and the prop noise I would be very happy indeed. It seems that the sort of quietness I am looking for IS available - it is now a matter of getting it going on my planes.

As I see it the object is to smooth out the sharply rising pulses (bangs) from the motor which will then lead to a far quieter system.

Back "home" in Africa there was no problem at all, but here in UK people are very sensitive to noise, and I have found that I am also becoming sensitive to annoying noises.

Charles

Hi Richard!

Good to hear from you. Could you drop me an email sometime, also with you your home and work phone numbers so we can have a chat?

I'd like to hear about your electric Smoothie too

Best regards

Charles

Basically, people don't like to have a group of men hanging around all day. There was an RC glider club that got run out of a park, bascially for that reason. The noise is the leverage, but the real reason is something else.

We've had neighbors oppose converting abandoned RR track to bicycle trails for the same reason. Ditto canoeing of rivers.

On the bright side, there's the new fad of BOOM CARS. They have enough power to make other cars resonate 300 yards for the source. I can't figure which car is emitting the rap. A model engine is something of a relief.

Yea, we have cars like that here too - you can almost see the metal sides bulging in and out with the bass. Deafening in my car at the lights when they're behind or in front of me - goodness knows what the sound level is like INSIDE!

We also had someone complain about the "noise" of the RC gliders - LOL. There are some who LOVE to complain.

But seriously, I do want my motors to run VERY QUIETLY - if I can

Charles

>>Someone mentioned "Scott Dingers mufflers".
>What
>>are they and where can they be purchased?
>>
>>Guy Blankinship
>
>Check the "Links" page on the DMAA website
>
>http://www.DMAA-1902.org/
>
>Bill Lee

Whoops! Had a bad link. Fixed now.

Bill

Very soon, now, I will have my rebuilt and re-engined Bi-Slob ready to fly. The Fox hawk .60 came with a muffler and I have left it on during break-in. Since I'll be adding tail weight I'll go ahead and balance with attached muffler.

I first flew in 1946. This will be the first time I've ever flown with a muffler.

A NOISY NOSE ANNOYS AN OYSTER.

I'm not a fig plucker, nor a fig plucker's son.
But I'll pluck figs 'till the fig pluckers come.

If you say this too fast you'll really need a muffler!

I live in a small town here in Colorado and I never had a problem with my engines being too noisy untill the last couple of years. first it was a new neighbor that moved in across from me, did not like me running engines out in my front yard. Was okay for him to get out with a string trimmer all day long but for me to test run a engine for say about 3 minutes was too much for him. And I live out of city limits also and no one out here ever said anything about noise no matter what kind it was. Next was in town, okay I kind of figured it might happen sometime, but thing of it is that this whole thing about engines being to noisy is a real problem, this year I got some more modern engines with mufflers and I am going to see what happens, I might be flying in the field next to my house weeds and all if this does not work.

Like I said, I want to build some REALLY quiet mufflers this year, so that if anyone complains I can say with authority "P*** O**!"

This thread has given me lots of ideas to try - and our club chairman has a noise meter. However it's the PERCEIVED noise that matters, not so much the actual sound level.

Charles

This is really why I don't have a flying field. I have about 6.5 acres and room for a circle at my property. But I have neighbors that will complain about the direction of the wind and expect someone to fix it. They tend to be loud and quite obnoxious when prodded. The guy down the street complained to the police when I was breaking in an engine behind my house at least 500 yards from his home with 4 houses and 10 acres of trees between. This is the same guy that builds hot rod jeeps and run his almost unmuffled V8s at full throttle in his garage at 11pm. The cop showed up but basically said I was violating no ordinance (I'm in the county and don't fall under the local town's noise ordinances) and well within general noise standards.

I asked the cop about putting in a flying circle and after I explained that the plane couldn't get more than 70 feet from me and about AMA insurance, he said that he could see no legal reason why I couldn't do it. But then we talked about the vocal nature of my wonderful neighbors and I dropped the idea. While I would be within the law, I wasn't prepared to be constantly defending against complaints and law suits and whatever other BS they were likely to come up with. These nuts can't even agree on a road association. It's unlikely they would ever agree to leave me alone. Probably wouldn't matter if I flew by magic and the plane was completely silent.

What about slapping him with a few complaints about that unmuffled V8?

Followed by - "If you shut up about my model plane engines, I'll leave your hobby alone".

I really can't stand this kind of NIMBY / BANANA * rubbish. Alas, Australia is chock full of the same stuff, hence my interest in the Fly Quiet after mufflers. The good old fashioned Australian "fair go" has been replaced with "I'll see your Lawyer and raise you a Barrister".

Strangely, the chief complainers seem to be the most obnoxious when it comes to inflicting their own noises. Case in point - a work mate of mine who got dragged into court multiple times because he put in a small pond in his backyard. That was fine, until some native frogs local to his area set up shop in the pond. This particular Aussie native frog makes a 'drip' noise a bit like a dripping tap. It drove one of his neighbours nuts to the point where he was dragged into court multiple times trying to force him to remove the pond. Didn't stop the same neighbour practicing playing a bugle (badly!) and driving everyone mad 'though.

* BANANA = Build Absolutely Nothing Anywhere Near Anything, seems to be an even more virulent form of NIMBYism which is popping up everywhere.