Noise.

[George J]

That's a very bad day out for Andrew.
For anyone thinking electric is louder than nitro, my Trex 550 came in at 76db and my Srimok Faifa was 79db. As Dentman has said most of the 50 size intros were 82db and as discussed some of the 90 nitros failed. (apart from Dentman's lovely Srimok N)
I really hope we at the club get this noise issue sorted out so we can get back to normal and just enjoy flying and watching others fly. It's such an lovely place to spend time and enjoy our hobby so hopefully it'll get sorted soon.

[Steve]

Steve and GravutyKills now you see the reason now you see why just making it look good for the club sound meter is no answer.

Exactly.

[trillian]

When they do the test, do they subtract the background noise level to get an actual reading of the noise level from the heli?

It's not as simple as subtracting one value from the other - you need a modicum of mathematical knowhow and a scientific calculator to work it out....

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This helps as well....

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That's a really good point that I never thought about. We did some sound level checks at our club last year but I don't remember the results now or if the meter was calibrated somehow to compensate for the background noise of the motorway.

The reality is that pure DB is also not an indicator of the perceived loudness because higher frequencies don't produce as much sound pressure but they can be more 'offensive' and thus seem louder.

I have not had my helis tested but subjectively my .50 nitros sound louder to me than the .90s. (the Predator gasser I suspect may actually be the loudest).

I'm not saying we shouldn't be considerate and keep noise levels down but it does annoy me somewhat that all it takes is one moaner out there to complain because their little world isn't just exactly how they want it 24/7. It's like the complainers seem to have a disperportionate amount of power, just one word and all the might of the law comes to their aid. But this wouldn't be the case if the noise was 'politically correct', such as a football stadium, a cricket match, the motorway, a military aircraft overhead etc. But it just seems like the 'powers that be' are all too keen to come running when it comes to shutting down model flying.

[Steve]

The point about an arbitrary (or recommended) dB level at a given distance is that in the absence of any other terms and conditions, the result can be fixed quite easily. Furthermore, if you know how to use a sound meter properly (and most people don't) and do the associated sums, then you can further increase your chances of making the model legitimately pass the test.

Simply holding a meter in front of a heli at 7m and getting a fail result of 83dB isn't the whole picture. A good portion of that noise will be background noise, and come from the wind, the EasyJet 737 taking off 2 miles away at Gatwick airport bound for Alicante, a sparrow farting in the hedgrow, the traffic pounding along the A99 500 yards away etc etc etc. You have to deduct the background level from the measured level to get a benchmark, and the background level will be different every time you use the meter. Different day, different wind etc.

The 90s will nearly always be louder on a meter than a 50. The sound meter is measuring sound pressure levels, and a bigger heli swinging larger blades is going to move more air, which equals higher pressure levels. It may not sound louder, but as been said already, it just sounds less piercing, more comfortable on the ear.

On the speakers on your hifi at home, the woofer is always bigger than the tweeter, because to generate lower frequencies at an audible range, you have to move much more air. It's the lower frequencies from the 90 that pushes the dB reading up.

[GravityKills]

>> Steve and GravutyKills now you see the reason now you see why just making it look good for the club sound meter is no answer.

I didn't mean that. With lowering headspeed via the governor (permanently, not only for the test), I was simply proposing a solution to get the heli's noise level down to the allowed limit that is cheaper than buying an F3C muffler.

BTW, I'm very well aware of the noise problem as I fly my 90 electric in a residential area and don't want to upset the neighbors. Keeping head speed low makes a huge difference in actual noise (from blade flutter, you wouldn't notice that in a hover test).

[trillian]

The 90s will nearly always be louder on a meter than a 50. The sound meter is measuring sound pressure levels, and a bigger heli swinging larger blades is going to move more air, which equals higher pressure levels. It may not sound louder, but as been said already, it just sounds less piercing, more comfortable on the ear.

Right. The point being though, if the issue is people complaining then what ultimately counts is what prompts them to complain. It would be more informative to hear different helis being flown as heard from the area where the complaints have come from to see what sounds are really carrying and noticeable.

I don't see where it's that helpful to have a situation where the sounds that people are complaining about are actually the ones that will pass the 82db 7 meter test where the ones that no one complains about fail. This would mean you could keep flying the ones that are actually the problem but assume that you could just tell them where to go next time they complain :-)

(And this may not be the case at all, it may well be that the .90 nitros are indeed the ones causing the complaint, I'm just saying the db meter isn't always the last word).

[Steve]

Exactly.

Find a new field would be my advice, one in the middle of nowhere where you can make as much noise as you like.

It's a slippery downward slope from here on in as Andy has testament to.

[pchristy]

When I started modelling many years ago, nobody used any kind of silencer at all! Believe me, an unsilenced Webra 61 at full chat is quite awesome! Not surprisingly, neighbours used to complain about the noise, and we lost an awful lot of flying sites. As a result, the BMFA in conjunction with the DoE (or whatever it was called then) drew up guidelines to be used when noise complaints were received. Note that these are GUIDELINES only and CAN (and have been!) ignored by Councils!

Having said that, most Councils do accept the guidelines as a reasonable code of practice. They are there for OUR protection, as well as neighbouring residents!

The BMFA guidelines are based on FAI competiton rules. For helicopters, these are as follows (paraphrased for clarity!):

The F3C rules specify that the noise measurement shall be made at a distance of 3M, with the model at an altitude of 2M.

The headspeed shall be hovering speed (ie NOT idle-up!), and the peak noise when the model is slowly pirouetted through 360 degrees shall not exceed 87dBA over grass or 89dBA over tarmac.

Now noise - like any radiated energy - follows an inverse square law, so if you double the distance you quarter the noise.

Moving from 3M to 7M - represents an increase of just over double, ie 2.333. So the decrease in noise will be 1/(2.333 squared) or 0.18 of the original level.

BUT dBA is a logarithmic scale, so a decrease by 0.18 represents a change in dB level of Log(10*(1/0.18)) - or -7dB (approx), so you are looking at figures of 80 and 82 dB respectively at 7M.

(Edit: Sorry! That should have read 10*log(1/0.18) - trying to do math formula in ascii text! Ugh!)

(The 0.18 is reciprocated when working out the log, because its a decrease in level)

Hope this helps reduce some of the confusion!

At recent World and European Championships, it has been unusual for any models to fail the noise test. However, experience indicates that electric models are just as likely to fail as IC powered models!

[dentman]

Pete, many thanks for your PM and your post, I believe we should all recognise what we see as an enjoyable hobby some will see as an annoyance and can't tolerate the noise ,with that in mind please be good neighbours , respecful and considerate to those around that don't fully understand why we fly toy helis/ planes in all conditions from the middle of a field!

[squeaky pete]

50 quieter?? bahahaha my old ely q comp, os55, ep energy exhuast spinning at 2200rpm hit 86db lol that was hovering at 2200rpm lol idle 2 lol