I have a general AMA Db Testing Question:

What is the ground surface required to be for proper AMA Db Limit Testing:
Grass?
Pavement?
Concrete?
Rolled Granite?
What?

I know that a lot of the clubs in the eastern US fly off of grass. Some fly off of Concrete, and some off of Asphalt....

So what is the rule specific to?

There is a major difference in Db levels when testing off any of the above surfaces. And our club is starting to become very stringent regarding Db levels.

(My plane passed with a 98Db (on Asphalt), but I would still like to know)

Any help, or knowledge anyone can impart would be helpful

Thanks,

Dave

Without researching again, I think the AMA DOES NOT SPECIFY any specific sound limits.

Certain Competition Rules do do so, such as RC Pattern. EDITED to add: Competition Rules are established by the AMA members participating in various competition disciplines through the Contest Boards and their established procedures.
Then there are FAI rules, however your question was not aimed at FAI.

Of course individual clubs and associations are perfectly within their rights to levy specifications to suit their own particular circumstances.

Pattern and IMAC both have sound limits in their rules which apply ONLY to the planes flown in those events.

However, many clubs have adopted one or the other testing method and limits for use at their fields. Take a look at the AMA Competition Rulebook for each event to see the what and how of each testing method and limits.

Hoss, you got it right. AMA rules wouldn't count for beans in controlling community noise emissions. Local ordinances apply. In most ordinances the limits on sound emissions are specified as an averaged dBA limit (typically averaged over a one-hour integration period) at a receptor's location (e.g., his property line), often modified with time-of-day and zoning offsets. When specified (in the US), the measurement method is usually an ANSI standard that is traceable to ISO 3744:1994 Acoustics — Determination of sound power levels of noise sources using sound pressure — Engineering method in an essentially free-field condition over a reflecting plane
The title of that standard is a giveaway to OP's query - the procedural standards for environmental sound level measurement generally specify 'over a reflecting plane,' that is, a hard surface.

Abel

Dave,

It is a lot like the gas mileage stated on the window sticker of a new car. Not very meaningful in the real world, but pretty accurate for comparison. What your club needs to do is establish a specific measurement standard of its own. How high off the ground is the plane, how high is the mic, where is the mic relative to the plane and exhaust, and what surface it is measured over.

After all, these measurements are not very accurate compared to what is being produced in the air (no reflictivity, higher prop rpm, etc.).

Good luck,

Bedford

That's a good analogy. It may not be the best way technically, but it is most likely the way it is specified in the local ordinances, if allowable levels are specified objectively at all. Let's face it, if you have to answer to a noise complaint your primary objective will be to demonstrate that you are in compliance with community standards as stated in the local ordinances. No matter how technically superior an alternative way of making the sound level measurement one may devise, it is bound to be less convincing to responsible authorities hearing the matter than if done in exactly the same way a cop with a sound meter would do it.

BTW, ordinances regulating environmental noise rarely/almost never regulate source levels, but rather levels received by a receptor in a noise-sensitive location (school, library, hospital, residence, et al). For example, OP stated his club standard was 98 dB, and I'll guess it was measured at 9' per the old AMA recommendation (or 3 meters, as recommended by Steve Kaluf to be consistent with international competition rules). The received level can be estimated at receptor's location by assuming spherical spreading. By this estimation method, the spreading loss at 1/4 mile would be 20 log (1320'/9') = 43 dB. A fairly typical ordinance limit is 55 dBA during daytime hours in rural and suburban residential areas. OP's club limit on source level of 98 dBA - 43 dB spreading loss at 1/4 mile yields 55 dBA for the received level at that distance. Seems like a reasonable limit, if nobody that would potentially be annoyed lives closer than that distance from the flying field. Probably not good enough to leave it at that, though. If the need to defend against a noise complaint were to crop up, the club would be in a better position to argue they are in compliance with community standards if the levels projected by engineering calculations were backed up by actual survey data. Our club has conducted such surveys on two occasions, several years apart. We have had encounters with a chronic complainer - but have kept ourselves armed with the necessary data to defend, and have done so successfully.

Abel

OK, theres a lot of info above.

My question is this: WHAT is the AMA's standard Testing procedure?

what is the material under the aircraft supposed to be?

Example: If I test on Asphalt at 100Db, I may only be at say 91Db when tested over grass, and only 93Db when testing over dirt.

IR-regardles of what local DB Limitations are, or how THEY test, how does the AMA Enforce Sound limitations at all of their registered sites?

IS there a uniform test? and what are the guidlines to that test?

Hossfly & beepee this is why I am asking. So that our club meets the UNIFORM TESTING PROCEDURES for the AMA for DB LIMITATIONS @ a flying site.

example: we take off of a paved runway, and fly over open desert. Where should we conduct the Db Test?

The aircraft is only on the runway for 10-12 seconds before becoming airborne. So should we test there, or over the open desert which is our true reflecting surface?

How does the AMA Test for Db limits at the NATS? is it over grass, rock, dirt, concrete, or asphalt?

See my reasoning?

It is all covered in the AMA Competition rules:

http://www.modelaircraft.org/events/...aerobatics.pdf See section 5 starting on page 2.

And another piece of enlightenment: Re: "how does the AMA Enforce Sound limitations at all of their registered sites?"
There is only one AMA site, and that is at Muncie. Sound limitations apply only to certain rulebook events. Except for specific AMA rulebook events, sound limitations that may be in place at club flying sites are enforced in any manner deemed to meet the requirements as set by the club. The AMA has nothing to do with this on the local level.

Is there some reason people will argue a point to death rather than going to the AMA web site to find out the information?

Curious that they specify 25 feet as distance for the sound level measurement. I could understand 23 feet, as it would then effectively equal the 7 meter separation that is frequently used in Europe.
The allowable levels are surprising, too. The 98 dBA @ 25 ft limit corrects to 107 dBA @ 9 ft where we usually measure at clubs. That is painfully LOUD, and can cause permanent hearing damage in short order. I wonder if there are any clubs that allow levels that high???

Abel

I don't think that there are many clubs that have any sound level restrictions unless imposed by local conditions or ordinances. If such are in existence they usually specify how it is to be measured.

No, not by AMA which is not a controlling authority, nor by controlling authorities which in the US are usually county subdivisions or smaller.
some states (CA for example) have prepared model noise abatement ordinances, but these are recommendations to local political subdivisions, not mandates.

Abel

Some if not many do, and AMA's IAC is one site where such restrictions apply (maybe, it depends.......): The limit is 98 dBA measured at 9 ft.

OP asked "IS there a uniform test?" Obviously not as far as AMA is concerned. I presume Scale Aerobatics is flown at the IAC, and the rules for that event allow 107 dBA @ 9 ft. I don't even want to know what sound levels are allowed for Pylon racers.

Abel

That is incorrect. The Scale Aerobatics rules define the limits as 96 dBA over soft surface and 98dBA over hard surfaces measured at 25 feet. There is no measurement at 9 feet and no limits set. That is what you calculated it wold be at 9 feet. But since that is not how the measurement is defined it really is not correct to say that is the limit for Scale Aerobatics.

In fact, the SA rules also allow for in flight sound scoring and that is what most contests now use, even the IMAC NATS held in Muncie if I recall correctly.

As far as I know pylon does not have any sound rules for their events.

Can you point me to a reference for this?? I am not aware of any such guidelines or other state or municipal codes that apply specifically to model airplanes. I would very much like to see them since I live out here.

You mean like the people at my club that INSIST it is an AMA rule that you have to have a spinner on your plane?

Bill-

Seems I created some confusion - sorry about that. I was referring to a model for noise control ordinances, not ordinances that apply to model airplanes. FWIW, [link=http://home.netvista.net/hpb/calnca.html]here[/link] the CA act that authorizes the model ordinance(s), paragraph 46062 applies.

Abel

It is not incorrect unless my calculation is wrong. Possible, but this is Physics 101 stuff, and projections from measurements at one point to expected levels at another distance by the spherical spreading model are routinely used in the industry. You can't reasonably measure everywhere, so you interpolate/extrapolate as necessary to fill in the blanks. As I mentioned in an earlier post, it's a good idea to confirm such extrapolations on occasion to validate them. This has been done countless times, more than sufficient to validate that the mathematical model used to represent the physical process is reliable.

Abel

While that may be physics.... it isn't the rule....

you will never be measured at 9ft at an IMAC event........

Interesting discussion.....I took some readings for my plane in each of the quadrants and the LOUDEST was directly in front of the plane! I would assume it would have been at the rear or back of the plane.

And David, I was told 'all planes have to be sound tested'...so even before my son flew he was asked to have his measured - and of course we put on a new prop the night before but it came out to an even 100dB at the 'dotted' line (circle) that was 'expertly measured'.

I still contend the REAL measurement is the noise level measured along the 'Dam' to the south....but that doesn't count So if I see you out there on Saturday morning - be prepared to me 'measured'

Jerry