Hi i am new to this well new compared to all you
i have been flying for under a year and learnt on my
irvine tutor 40 with an irvine 46 abc up front
now that i have passed my bronze test and can fly solo
i bought the thunder tiger 50 and put in an irvine 53
which by the way was no mean feet as the 53 comes with a
super quiet silencer that the IMAGINE dose not like so a bit of moding
on my part and a little squeez and hey presto its in just but its in
now the problem i have is that the plane faild its sound test and we have a limit
at our field of 82 Db
mine regesterd 85 Db
now i need to know how to quieten it down a bit
engine is in cowl
muffler is half in half out of cowl
Muffler is touching fuse at the end
props used for test were
10X9 11X7 12X6

Hi!
Do you use a APC prop?
JK

tried an apc 12X6
and groupner 11X7

Hi!
And you failed using those props..??
Jan K

Yes both failed on 85Db
i have been told that the APC are the best for sound reduction
is this true?

Thats odd..... ITs a really low Db setting 85. Almost any glow engine will trip that. How were the measurments taken? Truth be known the right way to test Db is from 8 ft away and 6ft up, or vise versa I forget but its either one of those. I bet you make it in if you test like that.

One thing you can try is a silicone exost extention. And if that fails reduce your throttle end point at WOT.

Peter:

Two things. You say the muffler is touching, this will cause the entire plane to resonate and raise the noise level. I'm sure you've been in an auto when the exhaust hit the body, remember how loud it was?

The other is going to a three blade prop. This allows a smaller diameter at the same pitch, lowers the prop tip speed, and thereby lowers the propellor noise.

Concerning he APC props. it's subjective and not supported by any measured tests, but to me the Master Airscrew props are quieter than APC of a similar size.

Bill.

They have an 89db limit at one field I fly at. My Magnum 52 with a Master Airscrew 11x6 was several db too loud. Just switiching to an APC of the same size brought it down to exactly 89 db. An 11x7 would have been even quieter. The club members told me that a switch to APC brings most of the violators within limits.

Ernie

As others have mentioned, 82 db is really low, although of course it depends on how far away and where it is being measured from.

At our field 95 db is the limit and lots of stock engines don't make it. I think they meaure it about 10 feet away, and they measure the sound from all directions. Most of the large motors, particularily the gas motors don't meet the limit, some guys have spent hundreds of dollars trying different mufflers & props to get to the 95 db limit.

I have had my OS 46 FX and OS 61 FX measured for sound, they registered a peak of around 89 db. They use the stock mufflers (i.e. with baffle), and are very quiet. I have found that the large diameter, low pitch APC props are pretty quiet.

Malcolm

As many have said 82Db is low but we have a professional complainer that
lives near our site and he got the council out to sound test and they came up with
the 82Db
i placed some wing tape around the inside of my cowl as there is a 3mm space
all around and i re cut the holes for the needle valve and such as to increase
the clearance
i have also re-cut a new scoop for the muffler but there is still some contact
and i don't think i can cut anymore out
the muffler sits at a strange angle and there is no way that i can see to
straighten it up
what i would like to do is get an extension for between
the engine and the muffler that would push the muffler out just enough
to clear the fuse but i cant find any where on-line that does them
and my local model shop has no idea what i am talking about
this is a pain as i have only flew it once and loved it

HEEEEEEEEEEEEEEELLLLLLLLLLLLLLLLP................. ...........

Hi!
Getting the silencer more outward is simple! Just fit a spacer ...let´s say 8mm thick of aluminum between the silencer and the engine.
Make it yourself by sawing, drilling and filing...have done this myself on several engines...works fine. Just get longer Allen bolts for the silencer!
As for props try a 11x8 or a 11x9 APC I would not try a 3-blade prop as most of the time they are inferior to 2-blade props performance-wise and as loud or louder.
APC props is regarded amongst fliers around the world to be the most silent prop available on the market. MA props are about the lousiest, loudest, with worst performance props you can get your hands on... Why do you think competitors mostly use APC?!

As for silencer Is it a doubble chamber silencer you have ?

Regards!
Jan K
Sweden

Are you sure you understand the council's 82 DB rule? Most sound ordinance laws are the maximum DB at the edge of your property, not right next to the sound source. Often 65 DBA is used and is easily met with a plane set up at 94 DBA.

OS, Du Bro, and Magnum all make those spacers for around five bucks.

Ernie

I that you carb sticking out of the cowl? I read an article a while ago, so I don't remember it clearly, but I thought I remembered something about a bit of noise coming from the carb. Since it doesn't fit in the cowl, you might try puting an air filter on it. I have never tired this, so I have no idea if it will reduce the db, or if it does by how much. Maybe someone else has more info on this.

82dB(A) is the National UK limit for noise from an R/C aircraft. Measurements are taken at all 4 sides of the model, at a distance of 7m (22' roughly) from the model. so at 10' that's about 88dB roughly that has to be met.

People in my club with an Irvine 53 have had success using the standard silencer in its full form (not sure if you modified the silencer or the model to make it fit) and a 12x7 or 11x8 APC prop, but you can also get through with a 12x7 Graupner. FWIW our club imposes an 80dB/7m noise limit on all models <1cu.in, and in general the main solution is to run at less than 10k rpm, which obviously makes 4-stroke engines our preference!

Regards

Chris

Bill, my experience has been that the MA props are nice and quiet, maybe even quieter than the APC, when used on lower rpm 4 strokes. Put one on a screamer though, and it's a whole different ball game!

Ernie

Ernie,


Master Airscrew regular props (black) may be quiet, but this may be a result of the blade 'flattening' as RPM rises, reducing its pitch.
This also allows the engine to gain RPM.

Anyway, changing to a prop with similar diameter and pitch, form APC, Bolly, or the MA Scimitar series; although RPM is reduced somewhat, invariably results in the model flying visibly better; faster and with a much better vertical performance.

I use my remaining remaining black MA props (11x6) in trainers and in slower flying models.

Thanks for the info i have just mailed Just Engines
and i take it form most of the posts that APC are
the best so will go out and get a selection to try
hopefully this will get me passed and flying again

Mort.........................

Actually it is quite because of its square tip. The TF Power Point props are also noisy because of the sharp tip. The flatening --Manually flattening out would actually increase noise as the engine picks up RPM. IMO the Zingers and MA wood props are the quietest .

the MAS will usually run faster AND quieter than the same size APC....performance is a different story


dave

HI!
Strange......APC is regarded as a very quiet prop...more so than MA because it has more modern tips and shape than most other props (MA). Square tips produce more sound than pointed tips.
Running two-strokes under 10000rpm is no problem....

Jan K

how they compare at 10K RPM i don't know. i'm talking about 15K+ with 7"-10" diameter props. only noticed it because i was bench running a couple of engines with a very quiet multiple muffler setup. the fact that they run a bit faster despite the much wider tip must mean that they're flattening out...this could be the reason that they're quieter.

but then what happens when they unload in the air? don't know as the after muffler stays on the bench and the exhaust is all i hear. either way they don't perform as well as the APC.


dave

This was put to me by a friend i have the super quiet silencer
the one with the extension and it has only one baffle in it
now if i use a second baffle will this reduce the noise and
will it add to back pressure?
if so what effect will this have on the engine life and running?

Mort...................