ZDZ 210 is two noisy?

[Cracky]

Hey Mark....I got an idea......get with Bud Light and get them to open up a Bud Light Aerodome north of Lake Saint Louis.......NO Warbirds or Circle Flyers and No noise restrictions....

[dmichael]

Educating decision makers in a club, modeling organization or - worse yet- an outside group like a homeowners organization about what is an effectively muffled power system can be a tricky task - especially when it concerns large gasoline engines. For those of us who have been around planes with the "proper" prop, engine and exhaust setups designed for the lowest possible in air noise levels like the one you have, we have become aware that measurements taken on the ground can provide little or no prediction about if a plane is quiet in the air. Perceived noise levels when flying is where it actually counts, not on the ground.

I have witnessed large gasoline powered engines equipped with three bladed props and cannisters that, when held to the standard "db test at X feet on the ground" were measured to be noisier than much smaller glow powered planes. However, when in the air, the glow powered plane was easily the noisier of the two planes.....

This dynamic is why IMAC instituted an in air score. The IMAC sound committee did exhaustive work to try to find the best way to predict how to properly equip the large gas powered planes so that they put out acceptable noise levels in the air. In the end, their conclusion was that ground testing really didn't help much. The in air score was a way to judge and manage how loud a plane really was in the air where it counts. You might ask why the ground testing wasn't scrapped? IMAC cites a few different reasons- the biggest was to meet AMA expectations on their effort to reduce noise.

I believe we saw a clear reduction in noise levels at IMAC contests as a result so the IMAC noise reduction is having an effect. Even so, the work is not done. The bottom line for your particular situation, however, is that ground measurements are not going to provide an accurate reflection of how quiet your plane is in the air and you may need to help your club understand this.

I apologize for the length- for those who want to see it, here is a statement from Wally Pitts, Sound Taskforce Chairman, on this subject:






"I have often been asked why we have a ground test. The short answer is: The AMA has (to my knowledge) always measured aircraft sound on the ground.


In the past it has worked out perfectly well for the AMA (F3A and Pattern). Unfortunately for IMAC (and the STF) the ground test has become increasingly troublesome. Most problems being related to aircraft size, prop size, and of course the fact that the test is taken on the ground, which is in itself a great reflector of sound.


Looking back it seems to me that the purpose of the ground test was to predict (in a fashion) what an airplane would do in the air. The theory being that the quieter the plane was on the ground, the quieter the plane would be in the air. To date, we have found this relationship to be non-predictive. As the STF started to study Decibel theory we decided to base our enquiries on the theory that we should be able to predict (by measuring a model on the ground) what it will dB in the air. To date we have found that no relationship exists between the two values (at reasonable ground measured distances). The ground test therefore has no relationship to the sound levels a model will generate in the air. Why is this? In many ways it has to do with the inherent reflective nature of the earth’s surface itself. When a plane flies through the air, it is surrounded by an "atmosphere" if you will, of air. Put another way, there is a blanket of air surrounding the plane for 360 degrees in every direction from the plane that not only carries sound but allows it to dissipate as well. On the ground the model looses half of that atmosphere to a highly reflective hard surface.


Complicating the issue further are the measuring devices themselves. It would be unreasonable to expect IMAC (or any other SIG for that matter) to invest in expensive sound spectrum analyzers, and distribute them across the country. So what we are left with are commercially available consumer retail units from Radio Shack (RS). Initially we tested various RS units in the lab (at General Dynamics) and found them to be within one dB of each other. So we quite happily employed them in the field as Pattern has done in years past. Unfortunately, as is the case with many systems, once employed in the field the inaccuracies started cropping up. It was not uncommon to find the RS meters consistently 2dBA apart on readings, and in many cases we have found units to be as much as 3dBA apart! When one considers the fact that the intensity of sound doubles for every 3.01 dBA, the use of the RS meters can (and has) given widely varying readings during the ground test. Another persistent problem, is that we have 40% 150cc powered planes on canisters (turning 32 and 33 inch two blade props) barely making ground test levels, yet recording readings in the air less than that of planes with engines half their size. These 40% planes are recording Very Quiet Sound Scores, yet are barely making the ground test levels! Having said all this the ground test will not soon be going away and as the RS meters are the only reasonable game in town and I still recommend every IMAC member have access to one.


Naturally then, one should ask, if the ground test has no predictive value, why do we have it? The answer is multi faceted. First we have it because the competition rules say we have to. The rules are dictated by a much larger organization of which we are but a small part. To be frank, there were those in this larger organization who were (at the outset) very skeptical of our sincerity, drive and desire to reduce the sound of our planes. Fortunately, we put solid work and established theory into our Sound Plan, and as a result we have a great working relationship with the AMA. A negative was truly turned into a positive, and we have a renewed credibility with those who make decisions that affect our SIG. This relationship will (in my view) bear fruit in other areas of IMAC’s relationship with the AMA as well. So in the end we have a ground test because it is of value. While not a predictor of airborne sound, the ground test does give one a general view of what levels might be expected in the air. We know for example that if one dB’s at 98 over a hard surface, one should not be too loud in the air. Conversely, if one dB’s over that same surface at 103, then in all likelihood a noisy flight awaits. Going forward it is my goal to have everyone think of the ground test as a Gateway, not an end all test.


So you ask, knowing all of this what do I as a CD do with the Ground Test at a contest? First keep in mind that we do not intend it to be the "end all test." Folks come to fly at our events, and we want to give them every reasonable opportunity to do so. After all, if someone is Too Loud, the In-Flight Judging Criteria will "catch" them. So in answering this question, we should again consider the inherent inaccuracy of the RS sound meters. Since there can be as much as a 3dBA difference in readings from meter to meter, you as a CD don’t know if your unit is on the high side or the low side. In my view, no one should be turned down from flying if they test within 3dBA of the limit. When this problem first surfaced IMAC began recommending that the use of ATV was appropriate for the ground test. Therefore use the Ground Test for it’s true purpose, giving competitors an expectation of what the plane will do in the air. Our recommendation: Never ground a competitor unless they are substantially (3dBA) over the limit."

[Chris Puckett]

It sounds like you have done what you can with that aircraft. You can test two planes side by side on the ground and the louder one on the ground might be the quieter in the air because the pilot knows throttle managment. I like the Roxana field except when people are shooting at you LOL I love the sound of the 210s.

[Cracky]

	Quote: Originally Posted by Chris Puckett
	I like the Roxana field except when people are shooting at you

yah, no joke.......

[martin18152]

Michael, I totally agree, my plane was tested on a flyby near the runway, at full throttle. The meter may have not been exactly 25 feet away; however, the db level was close to the mid 80s. I think our club needs to go back to the flyby technique. Some of those smaller plane screamers, with high frequency prop noise, around 15, 000 rpm, may not be putting out high Db sound energy, but they sure are annoying, can’t even here my engine, when those planes are flying, I wouldn’t band them, but we have to be real with our efforts. I think the club needs to reevaluate it methods, and use proven methods, the reason we use the ground test is because it’s easy, and if you’re a minority type aircraft flyer in the club, its easy to just pick something use it, as long as your not affected.

[notorious_benny]

I am really distressed to see static DB tests being imposed on 'gas' powered models.

You might increase the pitch you are running in an attempt to quieten the prop in the air. All that will do is cause the prop to cavitate on the ground and make a hell of a lot of noise. On the vice versa you can have a prop thats quiet on the ground but barks terribly in the air.

I have a 2.6 Yak that I have been flying for a year now, originally it had a da 100 with standards mufflers. In the last 2 months I have installed and been flying the model with KS 1060 pipes. WHen I first ran the motor at home on the ground I was dissapointed as I could not percieve a difference in noise output. However as soon as the model is moving its a different story! In the air I cannot hear my model above even a 4 stroke buzzing around at the same time.

I wonder if my club can appreciate that I have spent 700 bucks to try and quieten my model down.

I really believe the static ground test is meaningless, I know its nice to be able to set a number and tell everybody to stay below it, but at the end of the day its really not fair.

Put a well set up gas model in the air at the same time as a glow 2stroke or even a 4 stroke and prove which models are making the most annoying noise!

[xtreem3d]

mark,
i think i had your yak and kurt's mixed up w/ regards to the sound test...still shocked you didn't pass though.

[martin18152]

Kurt really got busted with the 3w engine. I was checking out the 3W props, and they have a 32 x 12 for $200, I wonder if any one has used a 32 x 12 three blades and zdz 210? Is the mounting hole compatible with the zdz, or is it smaller and can be drilled out? I don’t think I will buy one just to experiment, unless for some reason it gets better or equal performance. I plan on going up to the Roxana club this weekend, Saturday or Sunday, which ever is the best weather. I plan on joining, if someone is there to let me. Hope to see you up there Steve and some of the other SLRC 3D gasser guys too.

[aerojack]

Just spoke to Andy kane about the Fuchs 32x12 three blade and he says it is a good combo only if you have the KS1090 tuned silencers with it. Otherwise too much of a load. I have this setup here at home but have yet to run them together. When i do I will post the results here.

[aviti]

Mark - How far is Roxana from St Louis. I'm looking to get away from Buder Park on the weekends. I was out there yesterday and they were talking about a guy flying through the pavillion and hitting the fence behind it. Tony Vitiello

[Cracky]

I think its about 20 minutes from downtown.....take 55/70 East/North to 255 north......take the exit for 270 west and its about a mile or two is rt 111. Take 111 north (5 miles?) to a right on Wagon Wheel Road, take that to a right on Cemetery Road and that is the field....

[as722]

Talk to Andy Kane, he has the 210 on cannisters and a three bladed prop ( don't know which one) and his airplane is extremely quiet.

Albert