[Guest]

What dB level do most of these jet engines operate at? There are many clubs that have restrictions. MAAC does not have a limit nor does the Jet Committee. RC Scale Competition has an upper limit restriction and I am trying to find out just what the average level of these models I can expect. This may be something the RC Scale Committee needs to address.

Dennis

[Mike Emilio]

Originally Posted by Propworn

What dB level do most of these jet engines operate at? There are many clubs that have restrictions. MAAC does not have a limit nor does the Jet Committee. RC Scale Competition has an upper limit restriction and I am trying to find out just what the average level of these models I can expect. This may be something the RC Scale Committee needs to address.

Dennis

Just a thought, , ,

Would it not be better to get the manufacturers specs for the various engines?
Otherwise you might be risking knocking out a bunch of guys, if only based on opinion/speculation.

Also, take consideration for twins, or other multi installations like airliners etc.

[Guest]

As scale chairman it was pointed out to me that there is a dB level in the rule book of 96 dB (A) for all models. I am trying to find where and why this is in the rule book. I need to know the expected levels of the jet models so I can address this at the committee level. I have asked several sources including a manufacture or two and received no usable response. Manufacturers have said there are too many variables such as installation and model type and speed. In the interest of fairness to all I am trying my best to investigate this but have not had much co-operation at this point. I emailed the Jet Committee Chair through the MAAC web site and never even received a response. Not very encouraging. Before amendments are made to any rule book there has to be a reason and some supporting data. I am working on what I can control which is researching where this level originated and the reason behind it. Without something from either the manufacturers or the Jet Committee how am I to recommend amendments to the allowed dB level?

Dennis

[KAPTAN KAOS]

The IMAC or Scale competition rules say 96db on soft surfaces and 98db on hard surfaces. Turbines run in the 110db when measured on the gorund but have a different wave length and are usually exempt from the noise limits for this reason. The sound of a turbine does not travel the same as a gasoline powered enginge. FIA rules exempt turbines and a few clubs in Canada have also exempted turbines. My club is going through the motions of fine tuning the rules in regards to noise. MAAC does not have guidelines for tubines in regards to db's.

With gasoline engines there are things that can be done to quiet them down, such as pipes, different prop's etc. You cant put a tuned pipe on turbine.

Here is an extract from the Strathcona R C Fliers noise report.


Turbines are exempt from the noise restrictions
however may only be flown or operated during
the “normal flying” hours.

[Angus]

Something that is worth thinking about is how the sound dissipates. Db is a logarithmic value and it’s dissipation is different based on environment and frequency of each sound source

Are the db rules for the start-up pits? Or while the aircraft is in flight?

I believe there is some interesting data that needs to be collected and I agree with you there is limited out there.

An interesting note though; I would rather not fly my jets when there is a Gasser in the air at the same time as the Gasser tends to drown out the noise from the turbine.

AM

[Kelly W]

The way I see it, the current noise rule has only 1 purpose, and that is to gage / maintain limits on the amount of noise pollution created by a piston powered model aircraft in the air. This ignores what the engine actually sounds like (ie. a 2 stroke’s buzzzz, 4-stroke’s hummm, or a turbine’s whistle) This is currently done by equating the noise footprint to a sound measurement taken up close, where we can achieve good data since a piston engine will easily blank out the majority of any surrounding sound (as will a turbine).

Following that… We all have a good perception of the piston powered noise pollution at a distance, which we choose to extrapolate a pass / fail based on measured levels up close. From our history at the field, we all tend to understand the attenuation characteristics of this frequency spectrum, although this does not come as a result of any scientific analysis for the clear majority of those discussing it. As Angus just pointed out, it’s very non-linear so almost everyone relies on a gut feel for the conversion. That is where the fundamental disconnection exists which can easily lead to unrealistic expectations and political decisions; particularly if it happens that none of the people involved understand the science behind it. Thankfully, the few situations I'm aware of where this could have happened did not follow through to any sort of turbine ban.

How to compare apples to apples as best we can…? I don’t think its really possible since every result will be very subjective based on the assumptions used. Here’s an example… If we follow with a ~96db rule, calculate what a piston engine should produce at say ~600 ft distance, then equate it to a turbine, then back calculate it to a short distance for a turbine, the dB level will be through the roof (easily higher than the levels known to cause hearing damage…). I don’t need a calculator to know the result will be VERY high, easily higher than my PST-J1300R which produced ~104-106dB close up. That's an exposed turbine, not ducted in any way. If anything, this simply proves that the turbine should be exempt from this rule, but…… It’s also clear that a secondary purpose needs to be communicated and that is for the safety of those in the pit area. By that I mean since the sound levels are higher close up, clubs and pilots should work to provide an ideal position for turbine startup and agree on a suitable offset from crowds etc for their safety (since they are probably not aware of the risk).

That said, the above example wouldn’t even work in the long term since the curves will be different for each and every turbine, and there is a huge variation based on the RPM spectrums from the smallest to largest designs available. The span of frequencies for turbines is easily an order of magnitude larger than that of the piston engine spectrum. The frequencies created are primarily a function of mechanical noise (bearings and shaft assy), and aerodynamic noise which can change significantly from minor design changes or even manufacturing repeatability… Even if a manufacturer did produce a specification here, it would likely not have enough detail or be accurate enough to design a rule around it. The above example also falls apart when we examine what the purpose is, and what the distance should be. It could be a few hundred feet, up to a few miles depending on what the target audience is that we are concerned about. A few miles away from my local club, I can hear a 2-stroke if I listen for it. In comparison, I have tried to hear a turbine that I could plainly see in the distance at the same club and it might as well have been an electric foamie…

Also of note, the amplitude of the waves is not all that comes into play, as the frequencies involved are often higher than the human hearing threshold and thus the smaller turbines seem “so quiet”! I cringe when I hear people say they prefer the smaller turbines because they are quieter, meaning the hearing protection is seen by some as less of an issue! ??? Some frequencies will have more detrimental effects than others, and the levels we are dealing with are known to cause permanent damage. This further supports the club and pilots agreeing on a startup area offset from spectators and other pilots. It also reinforces that we all really should be wearing hearing protection…

Conclusion, the existing rule for noise pollution does not apply well, and it will not apply well if we were to push ahead and just draw a new line in the sand for turbines alone. However, a new rule is potentially justified on a case by case basis, not for sound level but to account for physical separation and safety when dealing with heightened sound levels up close.

Kelly

[DPO1]

A great deal of information may be gleaned from:

http://www.nonoise.org/library/envnoise/index.htm

Particular note should be made of the section titled "Atmospheric Attenuation". This section explains how (and why) high frequency noise dissipates rapidly with increasing distance.

The entire document provides considerable insight to noise production and attenuation.

Dennis

[Rcpete]

Hi all, my BVM P80 has a reading of 95.5db, measured with my AR824 Multi Range Sound meter.
Rcpete

[Guest]

Aside from the potential noise problem for our neighbours, remember that during the starting process, your are RIGHT THERE (emphasis only) and getting the full brunt of the 96+ decibels coming out of the machine.

I sincerely hope that you are using proper hearing protection, either through the use of earphones or earplugs rated for high-frequency noise.

It's not just the loudness and the frequency of the noise that does the damage but the repetition and duration that damanges the fine hairs in the inner ear, resulting in loss of hearing and partial/full deafness.

[Wayne22]

Hi Dennis, I understand that you tried to email me through the MAAC site, but I never received it, hence the no response... I'll follow up with the webmaster to ensure that they have the correct link to my email address.

There are no db guidelines for turbine powered models in Canada, nor in several other countries that I have been benchmarking with.

As the others have mentioned above, turbines emit a barrage of various high frequencies which will register larger numbers close up. The intensity drops off very rapidly with distance. In flight, turbines for the most part will fall in the lower percentile.

I can offer my assistance in finding out how other organizations (AMA, BMFA, IJMC, TopGun, etc) deal with this, but not until after the New Year. right now, the Jet Committee is busy finishing off the revisions to the Safety Code.

Regards

Wayne Beasley
Chairman, MAAC Jet Committee