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Does your club noise test turbine jets?

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Old 01-15-2013, 12:00 AM
  #1
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Default Does your club noise test turbine jets?

Hi guys,

Our club has recently decided to tighten up on noise testing of all models. Until now our turbine models have pretty much been left alone, but now the club management is looking to introduce a noise test for turbine models too.

It will be appreciated if you guys - whom already practice responsible turbine noise testing procedures - could share your experiences, limits and methods of testing.

Thank you for your input.

Cheers,

Jan
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Old 01-15-2013, 12:38 AM
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Default RE: Does your club noise test turbine jets?

Jan

The problem with turbines is that they will fail the 'normal' noise tests for prop driven models.

However the perceived noise being a a higher frequency is less and is less irritating to people than a chain saw noise at lower frequency. The noise level will be very different when taken from the rear compared to the front of the engine. The tests will also be affected by the height that the test is taken, the distance from the engine, the wind speed and direction. There is no 'standard' test that I am aware of. As you know turbines are often inaudible when a prop driven IC plane is in the air.

In Europe the noise issue is more of a problem with the strong green agenda.

There are inevitably people that love to complain. In the UK we have people complaining about church bell-ringing being too noisy or in the country cockerels making a noise. I have been involved with setting up a new club and found that much the best way to deal with it is to personally see all the nearby neighbours, and give them your telephone number so they can contact you directly. One of the closest to our club we expected to be a problem was the opposite and said she loved to watch the planes. The last thing you want is a complaint made directly to the owner of the land the club uses or worse the local council.

John

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Old 01-15-2013, 12:43 AM
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Default RE: Does your club noise test turbine jets?

A club of which I'm still (barely) a member of had an attack on jets.

The secretary (who doesn't fly jets) didn't get his way on an unrelated issue so he attempted
to stir up anti jet sentiment to hassle the other committee members who did fly jets.

The usual things, noise, fire risk, etc.

The fire risk issue was defeated by crash statistics we obtained from the American JPO website.

The noise issue was defeated by a sound report comparing a Boomerang Intro fitted with a P-70
vs a prop driven model of a similar size with a 160 four stroke twin. Both noise checks around the
models & on the residential boundaries of the field with the models in flight were used which showed
that the noise of jets was not significantly different to conventional models.

The secretary flys scale models so he agreed that the testing of jets should follow F4C scale model rules
for turbine jets. He didn't find out until later that jets competing in F4C scale events are exempt from
noise tests!

John.
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Old 01-15-2013, 01:27 AM
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Default RE: Does your club noise test turbine jets?

I'll be very keen to follow the responses to this thread Jan. Hopefully with some of the input here we can formulate a recommendation to the committee for noise monitoring which keeps everyone happy, and reflects the fact that jets are very different beasts noise wise.
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Old 01-15-2013, 02:16 AM
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Default RE: Does your club noise test turbine jets?

Guys,
Good questions

There is a formal UK process for noise testing for all model aircraft in the BMFA book, its really about prop planes but all local authorities will use the agreed Department of Environment noise test limits of a decibel count of 82(d)BA at 7 metres distance. My book is dated 2010 and makes the point that Gas Turbine noise dissipates faster than prop noise, so it was a work in progress with the JMA for a GT noise test then and I can't see any changes to that in the 2010 book update on the BMFA website today. Most jets seem much quieter than props unless there is a bifurcated pipe whining away.

In the absence of a recognised test I guess if a member of the public objected about noise the local authority could have a field day if they wished by using the prop standard.

Any JMA committee comments would be useful.

David
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Old 01-15-2013, 02:38 AM
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Default RE: Does your club noise test turbine jets?

We use the BMFA handbook recommendations for our noise tests, but increase the distance to 12M at the rear and include a variable for the size of the turbine, one thing I have experimented with is different efflux nozzles, they can make quite a difference to the noise output, but also thrust output as well, one other way is to overpower your jet, a 120 at half throttle makes less noise than an 80 at full chat.

Mike
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Old 01-15-2013, 03:44 AM
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Default RE: Does your club noise test turbine jets?

Hi guys>>


Our club is in a country town of 15,000 people and we are walking distance to the town centre. We are surrounded by houses where our downwind leg is halfway between the flight line and the nearest house. You can actually walk down the main street and occasionally spot our aircraft in the distance.


We had a round of internal stirrings about 2 years ago and what I found when we tested was that turbines would produce a greater sound pressure on a dB meter than your average 50cc gasser, however, as mentioned by Dave this is not a true representation.>>

>>

The doomsday crew cried that we would lose our field because of the noise and that the neighbours would complain to the EPA (Environmental Protection Authority) so I started to take measurements at different locations around the field. This is the same style of test the EPA would conduct as a Decibel Meter is the only true way to measure Sound.>>

>>

What I found was that the sound pressure produced by our aircraft – prop or turbine only made a small amount of difference on the meter above ambient at the boundary of our field and by the time you got near the houses the variations in the normal background noise was far greater than that produced by any of the aircraft.>>

>>

This being the case, the EPA (who have measured us) agrees that there is no real case for a “noise” complaint, however we/you can still be tagged as a nuisance much like the guy mowing the lawn next to you twice a day and pressure from the local council (government) can push you out.>>

>>

To help tackle this we put on a public display twice a year with free entry (but make a very good income from food sales) to get the locals involved which seems to work very well.>>

>>

In your case Jan, I would go to a Dick Smith store a buy a basic dB meter and start looking at just how much noise can be measured near those that could complain.>>

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Old 01-15-2013, 04:04 AM
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Default RE: Does your club noise test turbine jets?

Hi... we definitely have DB meters and are doing different types of measurements. The committee is generally supportive of jet operations, and have asked Jan and me to come up with a recommendation for noise testing procedures for jets. As with any club dealing with noise issues, there is a segment of mainly old timers who fly little planes who knee jerk cry "ban jets" at the first sign of noise issues. Fortunately (thus far) they have got nowhere with that. 

Nonetheless we want to be armed with knowledge of best practices throughout the world. There have been a lot of great contributions already to this thread. Your experiences at Sale are good for us to hear. 

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Old 01-15-2013, 05:05 AM
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Default RE: Does your club noise test turbine jets?

I was told not to fly a Wren SUpersport at one club because it was perceived to be noisier than other types of turbine.
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Old 01-15-2013, 12:09 PM
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Default RE: Does your club noise test turbine jets?

Ha, we cant hear our turbines because the field next to ours is crowded by control line combat crew. And they are loud...
My M90 is noisier than a P80, for what it is worth..
TP.
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Old 01-15-2013, 12:57 PM
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Default RE: Does your club noise test turbine jets?

Hi guys,

Thanks for all the input BUT please may I ask that you give us information to use in formulating a proper test regime.

Cheers,

Jan
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Old 01-15-2013, 01:45 PM
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Default RE: Does your club noise test turbine jets?

Well with respect I suggest coming up with a test you know you can pass :-)

What I mean is, you will have to get someone to agree that a particular jet is "OK" from an operational standpoint, and then perform measurements that establish that particular jet as a baseline in terms of distance and sound pressure level.

Because as other have said, if you run the normal prop type tests you will fail.
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Old 01-15-2013, 02:04 PM
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Default RE: Does your club noise test turbine jets?

if you can do the test with the wind blowing away your test position, it helps reduce noise signatures
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Old 01-15-2013, 02:18 PM
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Default RE: Does your club noise test turbine jets?

We use a distance of 7M in front, starboard and port and 12M behind, the sound level needed to pass is variable on the thrust size of the turbine, Wrens have trouble passing size for size as the whistle they have penetrates and puts the Db up quite considerably, the quietest on test has been a JetCat P80, we put this down to the size of the unit compared to thrust, a particular 90 I have did not pass until I put a different efflux nozzle on it, then it was down to the P80 level.

Hope that is what you want.
Mike
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Old 01-15-2013, 04:39 PM
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Default RE: Does your club noise test turbine jets?

The two clubs I'm member at are in isolated areas, no noise ordinance for any type of planes
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Old 01-15-2013, 09:09 PM
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Default RE: Does your club noise test turbine jets?

Noise problems are only a problem if someone complains and that usually would be a neighbor to the flying site. In our case we have NEVER had a complaint about noise from our jets, but several complaints with the very large 3D type gas burners doing 3D type flying without proper mufflers or prop size. In fact during one of the complaints face to face with a neighbor who was speaking on behalf of several other neighbors they had no problems or complaints about the jets in the air. Sure they are loud in the pits and on the ground but once in flight they are actually pretty quite compared to the 40%+ size birds.
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Old 01-15-2013, 10:17 PM
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Default RE: Does your club noise test turbine jets?

I was wanting to fly turbines at our our local club, but to do that we would need to extend the runway. I was lucky enough to have three friends with turbines to bring them out and put on a demonstration for the club. All the officers were there to see how loud they would be as we have neighbors half a mile away. What they found was that although turbines were significantly louder (as measured in db) on the ground, their sound would dissipate quickly whilst (thats for you guys) airborne and were actually much less intrusive than gasoline engines. It was decided that our sound level, 92db at 3 meters would not apply to turbines as the nature of the sound was so different that the existing test was not valid.

Maybe a demonstration including some people from the general public may help your cause. Good luck!
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Old 01-16-2013, 03:08 AM
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Default RE: Does your club noise test turbine jets?

Guys,

Please see below. This is all current BMFA policy but is seriously pre Gas Turbine. But its the NSP and POL that determines whether a noise complaint is valid.

THE CODE OF PRACTICE ON NOISE FROM MODEL AIRCRAFT 1982
The Code of Practice on Noise from Model Aircraft 1982 (the Code) doesn’t have the force of law and creates no offences. We use it as a planning tool and so do local authorities in their dealing with model flying clubs and their members. It will sometimes seem that it is being used against you. It is therefore essential that you do your utmost to understand the Code and to ensure your flying site will comply with its requirements.
The Code is included for your information in the BMFA Member’s Handbook, 2003 Edition, on pages 47 to 51.
The clauses of the Code are not as straightforward as they appear. Because of the way many clubs apply the Code a few words on the subject are appropriate.
1 The maximum allowable noise energy output should be 82dB(A) measured at 7m from a model held 1m above the ground with noise energy output readings measured at 4 specified points 90 degrees apart. The meter shall be in accordance with BSEN 60651:1994 (which superseded BS5969:1980) using the “A” weighted response and set to “slow”. The meter should be calibrated before use. The use of cheap meters is common. Any noise figures obtained with such meters should be treated with suspicion unless they have been calibrated before use.
2 A model noise energy output of 82dB(A) at 7m is deemed to be acceptable to listeners in noise sensitive premises (NSP) 500m from a model’s point of launch (POL).
3 The definition of NSP includes surrounding gardens.
4 The aim of the Code is to make your noise energy output acceptable, not to make your models
inaudible.
5 A noise energy measurement consists of 2 parts, the noise level in dB(A) and the distance that
the noise meter is away from the noise source.
6 For flying on uncontrolled sites the POL should be at least 500m from NSP.
7 Models should never be flown within 200m of NSP.
8 At sites used by clubs the 500m radius can be reduced provided the noise energy output is
mitigated to compensate for the reduced separation distance.
9 Silent flight models are exempt from the requirements of the Code.
10 The scales used for measuring noise are logarithmic in an attempt to mimic the way our ears
hear sound.
There are some common misconceptions:
A The Code was published by the Department of the Environment and NOT the BMFA.
B The noise energy emitted shall be the maximum value and NOT the average of the 4 noise
readings. For example a model reading 87dB(a), 81dB(A), 80dB(A) and 80DB(A) fails the test because the maximum noise energy output is 87dB(A) even though the average of the 4 readings is 82dB(A).
C With NSP say 300m from your point of launch (POL) you will get complaints if you operate your aircraft at 82dB(A) measured at 7m although your models meet the Code’s maximum permissible noise output. Your model will appear louder to a listener in his house 300m from your POL than the same model will to a man in his house 500m away. Even if you never fly within 200m of the man who lives 300m from your POL your model will be too noisy for him and is therefore unacceptable to him.
The Code is designed to make the noise of model aircraft acceptable to a listener in noise sensitive premises (NSP), usually houses, 500m away from a club’s point of launch (POL). For your models to be acceptable to this person the output of your model must not exceed 82dB(A) when measured by a noise meter of a type defined in the Code held 7m from the model.
The Code allows a POL to be closer than 500m from NSP. It also specifies that at no time shall models be flown within 200m of NSP.
4
For model aircraft noise from a POL say 300m from NSP to be acceptable then the noise energy output has to be reduced.
It is therefore implicit, while not being specified in the Code, that if your POL is closer than 500m from NSP then the noise output from your models must be reduced, otherwise the listener in NSP say 300m from your POL will hear a louder noise that the person 500m away. Nobody could blame the 300m listener if he complained about the noise of your aircraft as he is just as entitled to the same acceptable noise energy output level as the man at 500m.
If you find a flying site with NSPs closer to your proposed POL than 500m you will need to know what your maximum noise energy output should be. Under these circumstances we can calculate a reduced noise energy output level for you if you would like us to do so. However a rough rule of thumb is that your model noise energy output should reduce by 1dB(A) for each 50m your POL is closer to a NSP than 500m. (e.g. for NSP at 450m from your POL the maximum noise energy output should be 81dB(A)).
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Old 01-16-2013, 03:43 AM
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Default RE: Does your club noise test turbine jets?

David

One interesting point in the above that had passed me by was in clause 1 "The maximum allowable noise energy output should be 82dB(A) measured at 7m from a model held 1m above the ground with noise energy output readings measured at 4 specified points 90 degrees apart." The sound readings therefore do not have to be at right angles to the airframe, but at right angles to each other, this means that the readings at the rear of the airframe can be at 45 degrees to the jet efflux, this would considerably reduce the Db reading at the rear, will have to try this to see what difference it makes.

Mike
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Old 01-16-2013, 03:46 AM
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Default RE: Does your club noise test turbine jets?

David

You should read the BMFA Handbook which has a special section that relates to model gas turbines.

This states:-
Although the gas turbine is in scientific terms and internal combustion engine it is the BMFA's contention that the DoE Noise Code should not apply to it. The reason for this is that the noise code was written to cover the types of model i/c engines that were known at the time. i.e. piston engines and the concept of gas turbines was not even considered.

Read the rest of the section for more information.

John
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Old 01-16-2013, 03:49 AM
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Default RE: Does your club noise test turbine jets?

John

You are right of course, but that still does not stop some people applying the noise level restrictions at a club, its as well to be forearmed with the correct information, both the above are relevant to any situation that may occur.

Mike
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Old 01-16-2013, 04:19 AM
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Default RE: Does your club noise test turbine jets?

John,
You should read my first sentence, plus what the BMFA says may be interesting, but Ive given you the rules the local authority work to when assessing a noise complaint.

David
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