IMAC Noise level?

[mark786]

I just got an old Carden 30% without engine.
I am wanting to fly IMAC but am worried about noise limits as this plane will not accept a canister.
Is there an engine muffler combo that I can use and not have the sound problem?
Is the noise limit in Basic also?
What can I do to get this thing quiet?
Does it matter or can I fly with a Pitts muffler?
I have not chosen an engine yet so I am still flexible there.
Thanks,
Mark

[TheTank]

An ZDZ 80 single with a wrap-around muffler is relatively quiet when you run the right prop, like a mejzlik 26x10 or so. The newer higher power 80s would be around the same, but you would running a little bit larger prop. A very quiet option in that range is the ZDZ80-twin cylinder. A buddy of mine runs that motor on a H9 extra with mufflers and it is nice and quiet, so much so that it suprises me everytime I hear it run.

[mark786]

John,
Are you suggesting the the ZDZ80 with wrap around Pitts would be quiet enough to compete in IMAC?
I also just checked the link you have for jtec radiowave and they have a custom muffler with a muffler on it that would probably fit. Thanks for the link. I just don't know how strict IMAC is.
Mark

[RustyTumbles]

Without a canister or pipe your best bet would be to find a prop that works well but is quiet. It really depends on what motor you chose but generally the mejzliks or PT's are the quiet props, you just need to find the right size for your motor.

[Dangerous Dan]

you will be fine unless you rip the snott out of the prop, very few contests do a DB check, and if they do you will know ahead of time, if you are too loud you just adjust your atv until you pass. You get an in flight sound score if you don't rip the prop you will get 5's

Actually I have never seen anybody get a sero on sound. So to answer your question IMAC is not that strict, but when you start moving up you will want cans and a quiet prop so you can get 10's instead of 5's on sound.

[TheTank]

	Quote: Originally Posted by mark786
	John, Are you suggesting the the ZDZ80 with wrap around Pitts would be quiet enough to compete in IMAC? I also just checked the link you have for jtec radiowave and they have a custom muffler with a muffler on it that would probably fit. Thanks for the link. I just don't know how strict IMAC is. Mark

Yeah, an 80 on a wrap around muffler isnt too bad at all, and I am honestly a stickler about noise. Al at JTec had made me a custom muffler for my ZDZ 80 that I had side mounted instead of mounting inverted. It worked out great and was almost as quiet as the pipe i had in the airframe.

To go along with the other guys points, I have seen very few contests that have noise restrictions. One being a contest that I am hosting this weekend, but that is honestly a rareity unfortunately. Prop choice has a ton to do with noise, and event at my contest with a can-restriction or db limit if you dont run cans, we are getting 150s down to 97-98 dbs on mufflers, while using the ama testing method and 3 blade props. While most contests dont have a restriction, you will be given a sound score when you fly your sequence. The score given is either a 0, 5, or 10 based on your airplanes noise level, but this is scored very little in the overall scheme of things, but could become a factor if the scores between two pilots are very close.

Also, if you think you might be looking for a ZDZ 80, shoot me a PM, I have an 80 I havent been using on an comp arf 2.6 extra that i might be interested in parting with, but hadnt really though about it.

[mark786]

Thanks guys,
I assumed they were more strict than that and that they just would not let you fly. Sounds like I will be OK if I pick the right prop. I could also have jetec make a quieter muffler if needed.
What matters on prop selection? Quality or sixe? Do you go smaller and steeper to keep tip speed down?

John,
Thanks for the thought on the used motor. This is my first gas so I am looking around for used. I was considering a ZDZ but just got a lead on a 3W70 that I may try. If that doesn't work out I may contact you.

Thanks,
Mark

[Stainless Skills]

Do they inforce noise restrictions at competitions?

I have a DA 50 with a stock muffler and a 22X8 and it sounds pretty loud to me, would that not fly in IMAC or does it depend upon where you are? is there a standard?

[Dangerous Dan]

that would be fine

[sweetpea]

	Quote: Originally Posted by mark786
	Thanks guys, I assumed they were more strict than that and that they just would not let you fly. Sounds like I will be OK if I pick the right prop. I could also have jetec make a quieter muffler if needed. What matters on prop selection? Quality or sixe? Do you go smaller and steeper to keep tip speed down? John, Thanks for the thought on the used motor. This is my first gas so I am looking around for used. I was considering a ZDZ but just got a lead on a 3W70 that I may try. If that doesn't work out I may contact you. Thanks, Mark

	Quote: Originally Posted by Stainless Skills
	Do they inforce noise restrictions at competitions? I have a DA 50 with a stock muffler and a 22X8 and it sounds pretty loud to me, would that not fly in IMAC or does it depend upon where you are? is there a standard?

Noise is not so much an IMAC thing as it is a way to keep the noise down at the fields when larger planes fly all day. Normally its the field that wants sound enforced so they don't lose their field to the public outcry. IMAC/AMA adopted the 0/5/10 score because the Db check is really hard to do because with 30-60 pilots you would spend half the day just checking noise and like DD told you is easy to cheat at by changing your computer radio for just the check. Its just plain easier to have the judges do it during the flight (though not as accurate). Most planes will fit in the 5 score level. I've only seen a few planes that are loud all the time and deserve zero's. Most planes will rip a prop occasionally and just some throttle management will fix it.

No full throttle straight and level and the right prop will make alll the difference in sound. Cans are not 100% needed but they do make it easier to keep the sound down.


Also if sound is scored its usually enforced in all classes. You would need to check with the CD as that person has to submit to AMA/IMAC what rules they are not enforcing and it has to be approved. The CD is also supposed to put that information out ahead of the contest so folks know.

[Dangerous Dan]

Of the 7 contests i have CD'd We do a in flight sound score. Although the K is low I have seen sound be just enough to make a difference in scores and cost somebody a place. Typically 95% of all non zero scores are 6-9, this makes for some close races this is where sound can hirt or help you.

[exeter_acres]

Straight from the rules is posted below ....
http://www.modelaircraft.org/events/...aerobatics.pdf

We have not used it last year, but the sound meter was out 3 or 4 times last season here in the NC...
Also, :

	Quote:
	All Pilots that receive a Too Noisy penalty shall be notified of the penalty by the Contest Director prior to the next round. Pilots that receive a Too Noisy penalty will be allowed to adjust the aircraft setup and fly the next round (Known Unknown). Any pilot, who receives a second Too Noisy penalty during any Known, or Unknown, will be disqualified from further competition at that contest.

Sound rules...

	Quote:
	5.1. Maximum Sound Levels. The maximum ground sound level for all classes shall be: 96dBA measured on soft surfaces and 98dBA measured on hard surfaces. Contest Directors may implement a correction factor due to unusual conditions. 5.2. Standard Method of Sound Measurement. The sound measurement shall be taken with the sound meter set to the “A” weighting, slow response with windscreen installed. The sound meter shall be placed downwind, twenty-five feet from the model centerline and positioned in line with the prop arc at twenty-four inches in height (see Fig. 1). The sound meter shall be pointed directly at the model and perpendicular to the fuselage. The model being measured shall have its engine run at full power for the sound test. No noise reflecting objects will be allowed within three feet of the sound meter. 5.3. Ground Sound Level Test. Prior to flying the first round of a contest; each competition model must pass the Ground Sound Level Test. The Ground Sound Level Test must be completed at the sanctioned contest site by the Contest Director or his/her designee. Testing shall be done in an area designated by the Contest Director and may be completed prior to or during the first round. Models successfully completing the test will not be measured again during the contest unless their sound level is deemed to have increased significantly since the initial check by the Contest Director. Any plane that fails the test will not fly, but will be moved to the back of the flight order, and allowed one more attempt to pass the test. Any model that fails the second test will zero all judged SCA-3 sequences he would have flown during the current round. Any model that fails the second test may be tested again during future rounds with the same Ground Level Sound Test criteria being applied. No model will fly any judged sequences at any Scale Aerobatics contest until it passes the Ground Sound Level Test.

[Dangerous Dan]

judges must concur on sould score!

[Fly3DWithStyle]

	Quote: Originally Posted by Dangerous Dan
	Typically 95% of all non zero scores are 6-9

There is no 6, 7, 8 or 9. There's only zero, five or 10.

[Dangerous Dan]

	Quote: Originally Posted by Fly3DWithStyle
	There is no 6, 7, 8 or 9. There's only zero, five or 10.

You are correct for sound score, but for sequence 95% of all non zero scores are 6-9, this makes the sound score which is 98% 5 or 10, worth more than it would seem in comparision to your raw score prior to normalization.


example in unlimited sound is 12k so a 5 would be 60 raw points and a 10 would be 120 raw points. loss 60 points

Now figure 6 in the unlimited known is 30k a score of 6 would be 180 points a score of 9 would be 270 points a difference of 90 points.


get a 5 instead of a 10 on every sequence flown and it could cost you the contest!!!