The Gas Engine Decibel Thread
 

With more and more fields having Db restrictions, I thought it would be great to start a thread with this data, especially since gassers are getting more and more prevalent, and they tend to push or exceed AMA guidelines.

Please list:

Motor
Muffler
Prop
RPM
Surface
Decibel reading (3 meters)

Thanks!

RE: The Gas Engine Decibel Thread
 

Great Idea...[sm=thumbup.gif]

RCIginitions G26
Slimline Smoke W/A Pitts
Belia 18X6
7700 RPM
Grass
90Db

Brison3.2
Bison Smoke
MSC22X8
7000 RPM
Grass
92Db

Roto35
Supersonic Pitts
Bambula 20X8
6600 Rpm
Grass
88Db

RE: The Gas Engine Decibel Thread
 

Bad idea. Ground testing of sound has no correlation to the sound a plane makes in flight. If airplanes were only allowed to taxi, then your test program would have some merit.

RE: The Gas Engine Decibel Thread
 

Diablo,

While you are esentially correct every field I have been at measures sound at 9 - 10 feet to one side of the aircraft on the runway surface so in my eyes this thread has some definite merits. I fly at 3 of those types of fields so I am always looking for someone who has these measurements.

I feel it will help those who are concerned about sound at their field but that's just my opinion.

RE: The Gas Engine Decibel Thread
 

These are AMA testing guidelines. In any case you wouldn't be louder unless you got the prop barking. ;)

So I think it is very good information for everyone so they will know that if they buy a certain gasser, whether or not they will be able to even fire it up in the pits at the local club.

We've had to turn away quite a few lately, and I am sure many are left on their own with expensive experimentation to try and get the decibels down.

RE: The Gas Engine Decibel Thread
 

I totally agree with you this subject needs to see the light of day. The field I fly at has the same rule 98DB's at 3 meters (9ft.) and it was a hassle in the beginnig when I wanted to fly gaint scale.

Soon as I bought a large gas Engine the noise police came out of the woodwork, not knowing much at that time I thought they were picking on my type of flying, now I sure they are. i would grade myself a "5" out of ten for skills but I try to fly 3D and that's where the problem is.

3D is not something that my field likes or promotes, so you come under a different microscope than some body else without a muffler and waking up the dead flying a cub. [sm=punching.gif]

These are tests that I was a part of and can verify.
3w 100 (old style) with pitts type muffler it was about 3 years ago but I remember it being 104 or 105 db's[sm=thumbdown.gif]
ZDZ-80 my first one, with a pitts style muffler 104DB's[sm=thumbdown.gif]
Same Engine with a KS header and KS-89VS4 canister externlly mounted on a hanger 9 sukhoi 99 to 100 db's[sm=confused.gif]
ZDZ-80 blue head mounted on a hanger 9 Edge with KS header and KS-90VS4 mounted internally 97 to 98 DB's[sm=thumbup.gif]:D
Soon will be testing BME 105 with MTW 75 cans and in a couple months my new DA 100 with cans will post data on my web site.
Hope this helps
Thanks

RE: The Gas Engine Decibel Thread
 

Since the problem is caused by the noise of "flying" airplanes, why don't you start aiming your sound meters at the flying planes and figure out which ones are the noisy ones.

This thread sounds like the story of the drunk looking for his lost keys under the streetlamp. Did he drop his keys there? No, but he's going to keeping looking there because the light is better....:D

RE: The Gas Engine Decibel Thread
 

Because when I go to other clubs, and flying events (Pattern and IMAC), this is how I am measured before I can fly. It is the most consistent and standardized measurement that is recommended by the AMA and I believe IMAC as well. Sound readings in the air are too variable and inconsistent.

Maybe I'm just special... [8D]

RE: The Gas Engine Decibel Thread
 

Can't measure them in the air subjectly so measuring on the ground will have to do.

RE: The Gas Engine Decibel Thread
 

This reply is for bubbagates. Looks like you have some very low readings. Did you do anything special to get there? I did some preliminary measurements on my Zenoah G62 last summer and this what I got. Unfortunately noise measurements are becoming required by most clubs in the New England area. The measurement method previously mentioned is typically how it is being done.

Zenoah G62
Slimline smoke/Pitts style
6800 RPM
Mejlik 22x10
Grass
100 dB

RE: The Gas Engine Decibel Thread
 

Both the muffler and prop are working against you on this one. I've found the Slimline Pitts mufflers to be a bit louder than the Bisson with the tips opened up, and the Mejzlik is a lot louder than the MSC. A lot louder!

RE: The Gas Engine Decibel Thread
 

Roto 25V
stock muffler
7250 rpm
JAS 18x8
snow
84 dB @ 10 m
89 dB @ 3 m

RE: The Gas Engine Decibel Thread
 

Those cheap short stack exhaust with wood props are like old Huey helicopters, and train horns. You tend to hear them before you see them. In the politics of noise, big gas engines always loose.

RE: The Gas Engine Decibel Thread
 

Allot of my readings have to do with the prop being used. My G26 with a Mezjlik was tons louder (did not measure it) that with the Belia. The Belia prop is allot wider hence it turns allot slower. My Mezjlik turned 8300 and the Belia at 7700.

Supersonic mufflers are very quiet but they do rob a bit of power. Bambula props are very quiet and not too bad performers.

The Brison is fairly quiet and that surprised me to a degree. It seemed louder until we measured it and we did that from the front and both sides of the plane.

We use a cheapy Radio Shack meter and maybe it's not as accurate as most but I can tell you this, the Roto was definitely quieter than most of the glow engines and the Brison was flown with a few glow engines up there with it and was consistent.

I do have the Aerotrend blue exhaust tubes on ithe Brison and G26 to redirect the exhaust. That may be where the difference is.

Maybe it's a different kind of grass ;)

RE: The Gas Engine Decibel Thread
 

What's a good source to buy the MSC, Belia, and Bambula props? I was also using the cheapy Radio Shack meter.
I've noticed a difference in the noise output of a Bisson vs. Bennet muffler on a Zenoah G45, but I never actually measured the difference.

RE: The Gas Engine Decibel Thread
 

I think this thread is a great idea. I am measured at my field per AMA recomendations and at least at the other fields I have visited, the same rules have applied. It may or may not be the best way but it is A WAY to document sound level readings that people can relate to. It will also help me decide between brands of mufflers and props if a certain combination rountinely measures a few dbs lower. I know fields are lost because of sound complaints so if I can purchase a prop that is somewhat quieter, I will. I need a place to fly my expensive "toys"!;)

RE: The Gas Engine Decibel Thread
 

MVVS 58 With Mtw TD75k Canister Muffler:
94-96 Db @ 9 feet swinging a 24x10 mejzlik prop @ 6780 RPM

RE: The Gas Engine Decibel Thread
 

so I take it that the measurements are taken with the plane sitting on the ground at wide open throttle?

-Ed

RE: The Gas Engine Decibel Thread
 

IMAC gave up on ground sound tests. Most folks finally realized that ground tests don't correspond to the sound levels while flying - that's why they quit measuring at contests. Yes, ground sound tests are standardized. That doesn't mean they are beneficial to figuring out which setup is noisy in the air. Rippy props make the biggest difference and most folks don't have a plane that will rip on the ground. However, in the air, when the prop can unload 1000 rpm, some props get mighty rippy and noisy. Pattern planes don't have the power to rip props, so ground testing is OK for them. But this thread started talking about GAS engines....the prop ripping kind.

RE: The Gas Engine Decibel Thread
 

Correct.

RE: The Gas Engine Decibel Thread
 

I just got measured in Tucson last month... ;)

RE: The Gas Engine Decibel Thread
 

Flyfast1 wrote: That's correct with the plane on the ground, grass or ash fault 3 meters from the center of the spinner an even with the prop, on the down wind side, the meter held 24" off the ground at full throttle the reading is taken. I can tell you that a lot of larger glow powered planes will fail this test.

Diablo-RCU
We all know you are right, however we are not the powers to be and we have nothing to say about how the test is performed.[:o]
All of us only want to fly our planes not fight [sm=punching.gif]with other club members so we have to abide by there rules like it or not.

RE: The Gas Engine Decibel Thread
 

Don't fight with club memebers....educate them.
Show them how quiet a DA-150 is on in-fuselage cans when measured on the ground with an NX 32x10 prop. Then fly it at full throttle on a level pass........;)

RE: The Gas Engine Decibel Thread
 

If you want to get a good reading on the ground try this.

aircraft elevated at least 2-3 feet above a hard surface, plywood,asphalt,concrete whatever.
meter set at same level and at the 3 meters or 10 feet. this gives a little better reading.
as for a prop ripping just proves the pilot has no knowedge of proper prop selection to utilize the power of the engine.

RE: The Gas Engine Decibel Thread
 

Hi, I'm from Belgium and here sound requirements are very severe. I am experimenting for some 12 or so years now with all kinds of gear to soften the noise.
Noise is a very complex thing, for example there is a difference in the measured loudness and the degree of irritation it has on humans. So one can read equal amounts of db's but the one kind of sound will irritate people tremendously while the other does so very much less.
I think this has to do with what Diablo states.
This is one thing.
Another thing is indeed standardised measurement. Ofcourse when one has to meet some requirements one has to apply standardised measurements. They give no indication in how much the noise is going to be irritating people, it just is a way of comparing things.
What kind of noise is irritating, it is meanly .60 engines at 13000 + rpm or with other words high monotone frequenties. Even loudnesses of under 30 dba are quite nerve scattering.
4strokes are as loud as 2 strokes but they don't do so much damage because of the lower frequentie.The larger the engine the lower the rpm hence less enerving.
How to keep noise down? 3 things
a) keep rpm down
b) elastic engine mounts
c) last but not least a good muffler.....so NO slimline pitts and co. but canisters.
I know they are difficult to get rid of under the canopy but they are absolute must in this 3-points scheme.
Maybe you will say, I had a canister and I had only so much db's less than whith my "one volume straight out" muffler. That may be the case. It's a 3 points thing !!! take one away and it won't work.
Some practical things. Comparing the noise of props is only useful at equal rpm. My experiance is that some props are definitely quiter than others but that is mostly expressed in the higher rpm's... whitch we try to avoid.
RPM we avoid also in fly-style, so throttle down in dives.
Speed maniaks will have a hard time to keep the sound down....RPM.
Some planes will make more noise than others with the same engine set-up due to all kinds of amplification . Vibration will make everything sing that has play. Work away play in weels and controls and it will be that much quiter again......
So it's a matter of many things at the same time but don't worry.. it will still make noise and hopefully not enough to make your neighbours nervous.

At the end Je fais du bruit..donc je suis (freely translated" I make noise so I exist")