Hi all,

this post really is most applicable here in the UK where space is at a premium so that many flying sites have noise sensitive neighbours quite close by.

However, I am sure that the expertise is here to solve my problem!

The DoE (department of environment) here in the UK has a noise limit for model planes of 82dB(a) at 7m measured over graass. This is what we need to work towards at our regular flying clubs to maximise our "legitimacy" in the event of a noise complaint. However, this works out at quite a bit below the FAI limit of 92dB(a) over grass at 3m.

I am struggling to get my Alliance through the 82dB test as although it "sounds" quiet in the air it is testing out as quite noisy.

The model has the following setup:

YS 140DZ
Hyde mount
16x12 prop at about 8500rpm
Hatori manifold
Hatori 698 pipe soft mounted.

This is all fairly standard stuff and it does pass the FAI limit for being legal to compete with. However, it there anything I can do to reduce the noise further without compromising the performance?

For instance, has anyone tried an air filter type arrangement on the carb intake? Does it make much difference to the noise and would it have much effect on performance?

Would a different header be any quieter? Or would an additional add-on muffler on the end of the exhaust affect the noise or power?

Any thoughts and suggestions will be gratefully received.

thanks in anticipation,

James

James,
I've been doing some experimenting with different props on my Excelleron and found
the 3 and 4 blades are much quieter than the 2 blades. It might take some trial and
error to find the right size for your plane and keep acceptable performance but the
noise difference is very apparent. It surprising how much engine noise comes from the
prop.
Don Szczur , who won our national championship in FAI a couple of years ago , used an
ES Composites carbon fiber pipe on a YS 140DZ that was made for a 140 2-stroke. He
said the performance was as good as the 4-stroke pipe but it was the quietest pipe he
had ever used . The only issue might be fitting it on the airplane as it is somewhat
longer than the 4-stroke pipe.

Good luck,
tommy s

Hi,

living in a small and highly "regulated" country like Switzerland, we have gone great lenghts in optimizing our engines and planes with respect to noise. Laws in Switzerland are quite strict (and what isn't?)

What I found out, in random order (might not apply to you James or all others):
*) The engine ist not the cause #1 for noise problem: check for noise emission on retractable landing gears, control surfaces, canopies, etc. On a "sloppy" plane this can make out as much as 4 dBA, that's quite a lot! Of course this could not be an issue with most of the better built planes. Eliminate all noises not coming from the engine or exhaust - this is very important! Watch for any type of vibration (also from the inside)
*) Try using 3- or 4-blade props, this really helps. Again I can't say how much in dBA, but it's sensible. Bigger props help, too, and don't cost you as much power as you might think. The idea is to lower RPMs but maintain prop efficiency.
*) Props must be balanced, no matter what.
*) Engine noise can't be better dealt with than with a Hyde-type soft mount or silent-blocks (4 rubber grommets, 15x15mm). Always soft mount and don't listen to those who tell you that "you lose 10 to 20% of the power". This might be true (while I personally don't think so, but have no means to prove or refute the claim), but the available power ought to be enough for most of us. Hyde-type or other soft mounts make out as much as 3-4 dBA on most airframes.
*) On the pipe exhaust, a small piece (about 10 cm) of silicon tube helps to lower noise emission by approx 1-2 dBA

With my OS 140RX I read 89 dBA in 3m at my last contest in 2004. I believe 82 dBA in 7m should not be an issue.

Please note that no expensive measure was taken, what I described can be achieved with less than 30 Euros...

Regards,
-Fabrizio

James

A filter / silencer on the air inlet will help muffle inlet noise. Carbon / aluminum spinners "ring" when the engine fires and can be quieted by filling with expanding polyurethane foam. Both will be more noticeable to a meter than the ear. Lining the interior of the cowl with sound reducing rubber (available for instrument consoles) also helps.

Lowering prop tip speed will lower noise, lowering rpm and / or prop diameter will accomplish this. Prop material is another item to investigate.

James,

I am currently flying the Alliance with exactly the same equipment as you. I found a lot of noise is coming from my pipe coupler which is slightly loose. I am looking at other options at the moment. When I apply a little teflon tape around these fittings to make things tight again the model suddenly goes silent again . A flight or 2 later as the tape wears away the noise comes back.


Peter

I like what Fabrizio said: *) The engine ist not the cause #1 for noise problem: check for noise emission on retractable landing gears, control surfaces, canopies, etc. On a "sloppy" plane this can make out as much as 4 dBA, that's quite a lot! Of course this could not be an issue with most of the better built planes. Eliminate all noises not coming from the engine or exhaust - this is very important! Watch for any type of vibration (also from the inside)
This is what most people over look. I have used carb filters (little metal ones with mesh) on my OS's without compromising power. Not sure if it makes a big difference in noise though, but every little bit. I also used to put a bicycle inner tube over my hatori pipes to eliminate the metal *ting* from it.
One thing I did see most of the Japanese and a few Europeans doing was taking some foam (like the YS gray foam) and slicing it to about 4mm thick and gluing it over the plug and header holes on the fuse and then slicing it like a pizza (plug hole) so the igniter goes in. Also might want to put some foam on the belly pan surface where it goes over the wing.


Jason

You might also consider if you haven't already, isolating the wings, stabs and any other parts that are fesable from the fuse with a small bead of silicone.

Russell Honea
www.patternproz.com

You need to have a high sitting landing gear and calm weather. You can try by raising the model slowly from the ground and see the result in the noise meter. I think the noise measurement is quite stupid in the present FAI rules. I don't say it isn't needed, I think it should be made some other way. We are now measuring the wrong thing, not the real noise which is IMHO when the plane is in the air. Even electric planes fail the noise check on bad weather when strong wind comes from side. You can get terrible sounds from the propeller.

You might want to try some foam in your belly pan. A friend of mine has been working with acoustics and he told me you should use melamine sheet or similar open cell foam, that is the most efficent way to absorb noise. Glue some foam all over the bellypan, it weights nothing. I will try that trick next season.

Make a tunnel from foam in belly pan your cooling air intake so that the air flows directly to the engine. This helps little with the noise also and you will gain a bit more power for this as the engine runs cooler. Avoid openings around the engine if you can.

The smaller hole you have in the exhaust extension tube the quieter it gets. If you have a short 15mm extension try a long 10mm one and you will see the difference in the noise meter. There are commerically available external silencers you might want to try.

Try foam filter on the intake. It protects your engine against dirt, absorbs noise, has very little effect on the power, but is hard to get to stay on.

You might check that you have soft enough rubber isolators on pipe and header mounts. Put some foam tape between the belly and the fuse and make sure they aren't hitting each other or touchning anything else that moves like the header.

16x12 might be a bit light for the engine, if you get the RPM close to 9000 you will get some noise as the tip speed raises. Try 16,5X12W I like it a lot on 140DZ, another one might be 17x12N, I havent tried that one yet. Remember that with a four blader you loose some efficency and you double the tips (noise sources). This gives you an increase in the noise in that means, but you gain some as the tip speed goes down with the RPM. Different blade shapes have different noise levels... I think you should fly the prop you like best in the air and try everything else first.


Don't hit the 'secret weapon' and use a noise kill switch. I know many people do this in competitions but it is cheating and therefore stupid, isn't it? There is a more simple way: Warm up the engine a bit hotter than usually before the sound check and you will pass. When the engine gets hot it looses some power and you are ready for the measurement.

Overheating your engine on the ground prior to the noise check isn't cheating, Tuomas? Explain to us how that is different than some form of throttle limiting. They both cause no change to, in your words, "the real noise."

_Hopefully_ my days of thinking about what I have to do to pass the noise check are over.

So true. But the rules...

If you limit the throttle from opening during the noise check and after that release the switch and fly with full power you didn't have full power on the measurement. There has been at least one disquilifying I have heard, not sure when that was. If you heat the engine just a bit more and then go to the check as routine you loose 15s of time but you clearly have full power as the rules say you must have. I heard the guy who got disqualified was seen to use switch or was it so that they saw his throttle servo travel went bigger after the measurement. Anyway a noise kill switch is prohibited in competitions.

It is a trick you can use if you have to, othewise I wouldn't do it. My plane is just under 94dB anyway, I personally hate all kinds of tricks and worrying about the noise.

A well prepared plane will pass, no doubt about that, is there? Let's concentrate on that.

Guys,

thanks for all of these suggestions. There's some great ideas here, I will have a go at some and see what difference they make. Although it may be for a while, if the current crappy weather continues. OK (just) for flying, but no good for noise testing!

I should point out that it currently meets the FAI limits, it is the UK's DoE limits, which are stricter, that I am trying to meet. I am not expecting any one change to make a huge difference, rather a few small changes that hopefully will add up to a reasonable reduction in noise.

Thanks again to you all,

James

Thanks Jason,

I thought I put that one on top because I have experienced it more than once (loose canopy), and what a difference it made! Also what Russell Honea writes applies in most cases, I insulated my plane with a small plastic-like material called "Crepla" found in most hobbyshops and do-it-yourself type of stores, very light, comes in different thickness (1 to 5mm, maybe more) and glues to most materials with a small drop of CA. Carb filters are a good way, even better it is to look for carb air *behind* the firewall (inside the fuselage) using for instance a pre-bent fiberglass tube as air intake. (candles are btw a very good way for doing your own).
A good 4 blade prop, efficiently swung, generates less noise than a 2 blade prop, not balanced. Other sources that come to my mind: spinner caps, belly pans, canopies, servo hatches, bowden-tubes, tank and fuel line inside the fuse, antenna... In other words, pretty much anything!

As for "cheating" with the measurement, I'm sure Tuomas acts in good spirit but I can assure you that with very modest time and money investment (while building, a couple of hours and maybe 30 Euros) you can have full power AND stay safely below 90 dBA even in wind. My plane does 89 dBA (specs above), my former plane did 88 (Supertigre 2300, Greve pipe, 15x11 4-blade, averything softmounted on rubber blocs, pipe 'floating' inside fiberglass tube and suspended with fuel line).

We had to do it because otherwise we wouldn't be able to fly at all (remember, Switzerland...), but I couldn't personally think doing it in any other way: silent and clean - i like it! Necessity for us, but also a pleasure to fly - guaranteed!

Regards,
-Fabrizio

This is all very interesting even though we don't have noise regulations at our field. Believe me, I appreciate my luck every time I fly and I never take it for granted. I used to live in Europe, so I know how much you guys love to fly and the rules you have to live with. Maybe it will lighten up one day.

The tight wing fit with a soft seal suggestion is true. I found out with a plane that I could hear in the air. Tightening down the bolts hard made a lot of noise go away.

Covering makes drumming and high pitched sounds. Shrink down your covering before testing for noise.

Control rods vibrate a lot. I had one plane that buzzed loudly at certain high RPMs. Wood dowel rods vibrate a lot. You can isolate all rods when building the plane.

I was a helicopter pilot for years and the big noise factor for them is the blade tips. They approach mach speeds. On the particular helicopter that I flew, the tail rotor was the loudest sound when heard approaching from a distance because of the RPMs. We were taught that the Blackhawk has swept tips for noise reduction. A smaller diameter prop tip will travel slower than a larger diameter, so a slower tip may help a lot. Smaller props make sense if the higher engine RPMs don't get you...unless you use 3 or 4 bladed propellors. It sounds like you need to make a study by experimenting with sharp tips, blunt tips, and maybe rounded tips. You may find the right power/noise combination for your plane.

Even if it might sound unnatural, I actually think that these rules are a blessing, as far as I'm concerned. There's no need to "lighten up" anything, believe me...

There's a lot of noise coming from other sources, the world doesn't need any more noise coming from small model airplanes. No matter if near or far from people living in the neighbourhood. And it is possible to fly quietly AND powerfully, so why don't do it? It doesn't take long or a lot of money to get there, but overall quality improves dramatically.

I found out that high-pitched noise makes me nervous, because it's another input that my mind has to elaborate (I unconsciously listen to the engine, but there's no need to - except you have an unreliable powerplant, in this case concentration's gone even before the take off ). If you have a quiet, reliable and powerful engine you don't have to concentrate on this noise and can dedicate yourself to the actual flying - that makes me nervous enough!

It's true, we love to fly. I personally love to fly "quietly", another reason that made me purchase a Plettenberg and Lipos for my next project. But even standard pattern plane can meet regulations with little to no effort and can be VERY quiet with moderate effort. Regulations made it a necessity, but as I said I couldn't imagine doing it in any other way.

Regards,
-Fabrizio

A few things that might help.

1. Try a 17 x 13 instead of a 12 pitch. Your DZ has most of its grunt in the mid range, so lower rpm's work. Try reducing teh throttle a liitle with the sound meter on and see what you get. If you get what you want then you can experiment with propping down to that rpm.

2. ES Composites make a 2-c CF pipe that is very long and thin. It was intended to be used on the OS 1.40 in narrow tunnels. Fitting that CF pipe to a DZ drops the dB over an aluminium pipe. It has much more volume and is still very light.

3. An R/C car filter does work. (The Japanese have been seen using them).

4. I do know that a solid header radiates less noise but there's not much difference there.

5 Run the motor and touch the fusealage looking for vibration zones. If you find any, put a 1/4 sq balsa bar across from teh other side of teh fuse. Stops the micro drumming...
My Hydeway was noisy until I did this.

Just suggestions, not law :-)

Regards,

Eric.

And check your wheels, yep the wheels.
If they make even a slight rattleling noise when you spin them will your fingers, once the engine starts, that vibration is picked up in the whole airframe.
I changed a set of wheels last year after one fell of and was astounded how quite the airplane instantly became. This tight fit only seems to last for so long before they become "sloopy" again and the noise returns. Just goes to show how much they're rotating in flight because simply taking off and landing wouldn't ware them down that much.

BlaBla, we have been fitting axle hubs in the wheels we install in our line of custom gear we manufacture. These are nylon tubes purchased at the local ACE Hardware store, and are machined and fitted to the axles. We always try for nice snug fit. When these wear out, they are easily drilled out, and new ones re-fitted.

MattK

Wheels are a good one.

All my pattern planes have coil spings and washers that hold the wheel against the bushing of the axle. They serve two functions. First of all the wheels don't rattle. Secondly they create resistance in the stationary position before take-off. Once they over come the static friction they spin quite freely, until the plane leaves the ground and then the spring pressure stops them turning.

You set the spring pressure with the wheel collar. I usually run the motor with the plane inverted on a stand. Then just tighten the spring until the wheel stops spinning on its own. - Done!

Peter are you using a teflon coupler in the YS 4 cycle?

Matt

A bunch of years ago when we used to fly the 60 2 strokes, I used teflon couplers for a little while because they were free and easy to come by--I worked for company where I made the stuff for high pressure hose applications. The 2 strokes of the day would typically turn in the 10k-11k rpm range and my models tended to be more noisy than others. Then one day I was running the engine up and was looking at various spots in the model to see if a specific source could be isolated. Surprise surprise, I found that when I would touch the teflon coupler with a sili rubber pad, the noise would dissipate considerably and it would come back when the pad was removed.

I reasoned that the plastic is just too firm to attenuate the noise at 10K rpm, so I grudgingly went back to sili rubber and the noise was significantly reduced. It's been so long ago when I did this experiment, I had forgotten it

Matt

Neo02,

There is no way to quieten some of the bigger planes that fly at our field. We have a few of the bigger gas powered planes. One guy flies a weed wacker powered plane and it is probably the loudest. Some of the larger 4 strokes are loud.

I'm sorry but I politely disagree [8D] : there's always a way, but it won't be the easiest one...
If someone wants to quieten his plane, he can do it, preferably at building stage (it's easier), and it works for engines ranging 0,8ccm to 200ccm, 2 or 4 strokes or gas - it's all a matter of time and effort. What one needs is a soft mount designed for the engine displacement, one or more silenced muffler(s) and a couple of props to experiment with. I have seen larger gas engines (80 ccm) run almost like electric in a 3D aerobat, barely noticeable at idle and with a pleasant sound in the air, power not lacking at all.

Regards
-Fabrizio

Neo02,

Maybe some gas engines, but certainly not all or all of the noise. Weight is still an issue with some builders, so 2 mufflers aren't desirable. Soft mounts may take a little power away. Some people want the props that are the loudest or the really big engines. I respect your dislike for engine sounds, but not everyone likes the same things. A lot of members at our club enjoy the louder engines. A few run 4 strokes without mufflers. Personally, since I flew full scale for many years, I need to hear the engine to feel comfortable. It is a habit that can't be broken. I didn't even use extra hearing protection when I flew and thankfully did not suffer hearing loss of any kind. (I was tested every year) I can sense a lot from a good level of sound from my engines, and I depend upon it. We were talking the other day about having Walkmans or iPods at the field when flying, and almost everyone agreed that they would be uncomfortable not hearing their engines.

Not everyone can enjoy all things at their field. I sometimes miss the scenery of Europe and think of the beautiful fields that I visited there. Some people have noise restrictions and some don't. Some have ridiculously short fields or have hazards. We have to take what we are blessed with or without, and wish the best for all of the other r/c fliers elsewhere. If I had to fly under hardships or restrictions, I wouldn't wish that for anyone else just so we could all suffer together.

Agreed Fabrizio. The most interesting thing about generated noise is that our ears will get used to any noise level we fly at. Consider what we used to fly 20 years ago, with the piped 60's turning a toothpick at 17K rpm. Then a concentrated effort reduced noise to the relatively low and pleasant sounds that pattern planes are known for.

Now the problem for pattern people is when some other poorly muffled engine is running at the same time, and it simply overtakes the pattern plane. That used to be the case at my club because some guys insisted on 3D'ing their 35% gassie at the edge of the runway in constant hover. That and a dead engine contributed to one of my pattern models' demise a couple years ago. Never could hear the thing over all that racket, so when she quit, I found myself grasping for air and there wasn't any left.

Luckily, those models have since gone out of favor and we are back flying quietly, for the most part. Until some heli guys show up and insist on flying at 5 feet off the deck right over the middle of the runway, at full speed. That's loud too

I suppose to some, the obvious thing is to get the pattern planes louder. To me, that's the wrong approach. If most everyone flew quietly, everyone would be able to hear their model. M2cw

MattK