|
|
|
Sound Issues Revisited (Op-Ed) |
|
posted on October 25, 2009 22:49 
The issue of sound and IMAC planes will probably not go away until we are all flying electrics. With the introduction of new, more powerful engines, sound once again is becoming a hot button issue for most flying sites across the country. Unfortunately it doesn’t take a critical ear to note that, on average, IMAC planes are getting louder compared to just 3 or 4 years ago. There are many factors contributing to this including the aforementioned new engines but also we see our higher profile pilots spurning 3 blade props and canisters/pipes for 2 blade props and straight mufflers in never ending search for competitive advantage. The purpose of this article is to once again bring the sound issue to the forefront.
We can start the process by revisiting some of the work of the original IMAC Sound Task Force from several years back . In particular, the posting by Dave Von Linsowe1 reminds us the sound issue has been around for a long time and not just in IMAC. Take a look at the Prop Tip Speed Chart2 which shows the relationship between prop diameter, rpm, and calculated tip speed. Once the tip speed approaches .7 Mach, we have a problem! Lastly, for those of the engineering/scientific bend, this definitive article by George Hicks sets the standard for sound testing IMAC planes. It may be viewed by clicking here (PDF).
As some of you may know, the issue of sound has been a thoroughly discussed topic on the IMAC Forums. Everything from equipment mandates to changing the sound rules have been discussed in great detail. It has been accurately stated that in many cases, highly skilled pilots on many airframe designs can reduce the sound generated by their planes with careful throttle management regardless of the type of prop or exhaust. However, it is also very clear that even with careful throttle management, many of these planes are louder than they could or should be.
Let’s ask ourselves a couple of critical questions:
Is it enough to “fly just inside a ZERO”?
Our current sound rules give us little wiggle room in dealing with planes that are right on the borderline. Rest assured that the flying site’s neighbors don’t really care about your “sound score” as they start complaining.
Is it time to consider a different approach for sound control?
Our current rules put the issue of controlling sound in the hands of the judges. It obvious from even a casual examination of the score sheets that judges are reluctant to ZERO any plane for sound because of the relatively stiff penalty for getting two such scores and the peer judging process. Taking the judges out of the sound judging process using other approaches has also been a topic of discussion on the forums.
Our rules also call for a sound ground test…is it time to bring it back (enforce the current rule)?
The ground test using inexpensive sound meters is easily “manipulated” using throttle curves (or not going to full throttle) or skewed by different surface types. In the past, as pilots embraced sound reduction equipment (3 blades/cans) and the focus shifted to in-flight sound and the ground test was largely abandoned as unreliable and unnecessary. While it remains a rule, it is the single most unenforced rule in the scale aerobatics rule book.
Given the variety of flying venues, is a national sound standard appropriate?
It has also been noted that different areas of the country have little in common when it comes to sound issues. In the Southwest region for example, many flying fields are located in wide open spaces with few neighbors while in other areas, housing developments are springing up next door to our flying sites. You can be assured you will get different answers depending on where a pilot flies.
If you were flying IMAC at the beginning of this decade, you can recall the near panic generated by submission of a Rule Change Proposal on sound to the AMA Contest Board by a group that attempted to hold our larger planes to the same sound rules as the much smaller Pattern planes. At that time, the same Contest Board controlled both Pattern and Scale aerobatics. In effect, IMAC’s hand was forced to rush through their own counter Rule Change Proposal based on the preliminary work of the Sound Task Force.
It would not seem to be in IMAC’s best interest to wait much longer before taking a critical look at our current sound issues… history has a way of repeating itself.
1
| Written By: |
Dave Von Linsowe |
| Category: |
Sound |
| Date Posted: |
2/7/2004 11:26 PM |
|
Back in the eighties, F3A pattern went through many of the same sound issues that IMAC is facing. There are many similarities and differences that we can learn from. I personally would rather learn from someone else’s trials and tribulations than devoting a lot of time to reinventing the wheel. So lets look at what happened with pattern, the how’s, whys and what works to get quiet.
I first started flying pattern at the national level back in ’72. At that time we had to have a “muffler”. The muffler of choice was the flow through type, not very effective at getting an engine quiet! By the end of the ‘70’s most of us were using tuned pipes. Not to get quiet, but to develop more power. The style of flying was similar to what I refer to as the Blue Angle/Thunder Bird style. High speed passes with a maneuver in the center. It was possible to unload to 18,000 rpm in the air! My airplane was 112 dB at 3 meters! We were definitely the bad boys of R/C.
Over in Europe things were different. All the open areas were being built up. Noise became critical. The noise rules for F3A were established. Because of the international basis of the rules we didn’t have much to say about it. When they first started, the noise was measured from the four sides of the airplane and the airplane was on a platform off the ground to reduce reflectivity. That didn’t last long, as it was too difficult to conduct. That’s when the 3-meter, on the right side, down wind measurement rule was instituted. We also went to turnaround sequences to reduce our noise footprint. No one had ever done noise reduction like we were trying to accomplish. Everything was an experiment. The manufactures picked up on the things that worked and came out with more products for everyone.
The big problem was getting enough power and still getting quiet. It’s easy to be quiet; you just won’t have enough power to get off the ground! About this time it became obvious that some guys were getting louder in the air after passing the dB test. They had learned how to cheat! Because in-flight noise is what is really important something had to be done. That’s when in-flight noise judging was instituted. It was very controversial. We were there to be judged on our flying, not some completely subjective noise scoring. The noise of the flight was judged on whether it was “too loud”, “average” or “very quiet” and it was stressed that it was not to be relative to anything! Because the top scores were so close, the noise score became very important. The noise scoring really worked! It made all the difference in the world! Instead of just trying to meet the dB test, everyone was really trying to get quiet! We have to remember, and this is very important, the neighbors who complain and shut down a flying site, will be very subjective. They won’t care about dB testing. All they’ll care about is how noisy it sounds to them. This is why the IMAC In-Flight Sound judging Criteria is so important, and one of the main reasons we are doing it.
It was the addition of the in-flight noise judging that got pattern to the noise levels it is at today. If you haven’t heard a recent generation pattern airplane fly, it’s really amazing! The atmosphere at a contest is more like at a golf tournament. The airplanes are so quiet that you have to be careful in the pits of how loud you talk because the judges will hear it!
Pattern didn’t get really quiet over night and neither will IMAC. The equipment we’ll use in 5 years from now to get quiet doesn’t exist today! It’s an evolution. We’ll try things, some will work and some won’t. The manufactures will improve on the things that work and everyone will benefit.
We’ve started with some very realistic goals. Some will say it’s too stringent and others will say it’s not enough. Depending on the circumstance, both are correct. Local conditions will dictate what needs to happen in your area. On the national level we are committing to reducing the noise we generate to acceptable levels. If you are fortunate enough to live an area where you are not infringing on someone else’s right to peace and quiet (that usually means no neighbors within 4 miles of your flying site), no one is going to force you to make your airplane quieter. If you travel to attend a contest in another area be prepared to abide by their noise standards. On the other hand, if your area is noise sensitive, there may be noise limits stricter than what we’ve come up with. The information and methods that are coming from this initiative will help you meet your local noise requirements.
What we can learn from pattern and what we know will work.
In pattern, we didn’t have the luxury of another group coming before us; we started from scratch. Many of the same facts that existed in Pattern (as we started reducing sound levels) exist today with our IMAC airplanes. The number one noise source is the exhaust. We are all running some type of muffler/exhaust diverter so in some cases the next noise source that can be heard is the prop. After these two biggies comes intake noise and airframe noise. For a two-cycle engine, we learned in pattern that a tuned pipe became a must. Don’t get all excited that you can’t do it. We couldn’t do it at first in pattern. It’s part of the evolution. It’s factored into the evolution of the lowering of the dB limits with time.
Pattern didn’t have the excess of power that we typically have with an IMAC airplane, we can use that to our benefit. 3 and 4 blade props typically lost too much performance to be of much use with a pattern airplane, but we can use them to our advantage in IMAC.
With a pattern airplane, the next big noise source was airframe noise. One year I was getting the noise penalty, I only added the Vibra Damp soft mount and got the noise bonus the next year. With IMAC airplanes, intake noise maybe the next big noise source before airframe. Only testing and time will tell.
For now we’ve got the two biggest noise sources covered, exhaust and prop. With time these will be improved upon. As we progress to get really quiet we’ll have to also tackle intake and airframe. Those who take the time and make the effort will be rewarded and we will all benefit from it.
Dave von Linsowe Member,
IMAC STF
|
2
Wednesday, October 28, 2009 2:00 PM
I don't think a rocket scientist could under stand all of that stuff !!!!!
Thursday, October 29, 2009 9:57 AM
A "National" sound standard should begin with the requirements of the "National" flying site. What sound rule is going to be in place for the Muncie flying site? That standard would seem appropriate to be a stringent one. There may be other regions or venues that do not have this same standard though. Thanks Jim
Thursday, October 29, 2009 11:15 AM
It also doesn't help that the new engines are designed to produce more rpms. The engines are getting larger but to run well they are swinging the same props. 96db at 25 feet is also a very low reading. Even my quietest setup would have never been close to that number at my field. Carden with DA150, KS 1080, Mej 28.5-12 3 blade was 102 db.
Thursday, October 29, 2009 12:51 PM
"There are many factors contributing to this including the aforementioned new engines but also we see our higher profile pilots spurning 3 blade props and canisters/pipes for 2 blade props and straight mufflers in never ending search for competitive advantage." This is the biggest problem I have seen over the last 2 years of my involvement with IMAC. The lower classes look to the upper class and high profile pilots and try to emulate their set-ups and flying styles because them see that as successful. There is not the same stigma attached to having a loud plane as there was just a couple of years ago. Just my observations, Kevin
Thursday, October 29, 2009 4:51 PM
To my knowledge, no one has measured dB level of their sertup since IMAc stopped requiring it back about five years ago - even though it is in the rule book. Has anyone collected more sound data using the IMAC standards that they would like to share with us? Bobby
Friday, October 30, 2009 12:40 AM
I have db-ed my equipment recently. Running DA-150, KS rear stinger cans, Fuchs 30/12 wide blade-two blade, turning 5750, db 96 over hard. Same set up running Fuchs 30/12 three blade, turning 5300, db 93 over hard. Get all 10's on the three blade all weekend long. Get 1/2 10's and 1/2 5's on my two blade set up. Last time the two blade flew it got more 10's than 5's in a three day contest with someone else flying the plane the entire time. Oh yeah, it flew in the unlimited class. Looking at the tip speed chart above it's easy to see how these props get good sound scores at these RPM's. The solid blue line is the "no fly" line. Looking at the chart, you'll see a 30" prop is not supposed to break 6,000 rpm. A 32" prop is not supposed to break 5700 rpm (per chart above). If we stick to the chart, our sound problems are over. It's that simple...... Hope this helps, Dan Baker
Saturday, October 31, 2009 9:22 AM
I'd like to see the db rules put back into effect. Have the plane checked by a meter prior to going up, and a score given accordingly based on the conditions and factored with the quietest getting the 10 and so on. With that in place, see how quickly things clean up. In flight scoring too subjective and dependent on weather conditions Last contest I was in saw a DA 100 getting 10's for sound with stock exhaust. Don't get me wrong it can be done, but not that likely especially swinging a wood 2 blade prop. Wind was blowing out, and perseption of sound was effected by this. A meter measurement is the only fair way, and consistant.
Saturday, October 31, 2009 6:17 PM
Mr. Rhixer: All/any db rules that have been input into the IMAC FJ&G in the past four years are "in" effect currently. If you are at a contest and the CD is not ground testing the pilots for sound then you should ask, "why" at your pilots meeting. Make your voice heard. Dan,
Saturday, October 31, 2009 7:57 PM
I had the chance to do some testing today. 75 degrees on the hard runway at 1600 ASL. Aeroworks 260, MTW RE 3 DA 170 14" headers Mej 32-10 103 db momentary peak, but it fixed at 100 db quiet in the air Mej 28.5-12 100db momentary peak, but it fixed at 98 db VERY quiet in the air Aeroworks 260, KS 95 V5 DA 170 14" headers Mej 28-12 3blade 101 momentary peak, but it fixed at 99 db. quiet in the air
Sunday, November 01, 2009 12:56 AM
Mr. Quist: Were you able to get any RPM numbers on the props you tested. We would all like to compare your RPM numbers with the tip speed chart above to see how accurate it is. Your 32" prop is outside the current IMAC rule for gound testing, lets see if it is also above the solid blue line on the tip speed chart. Thanks, Dan Baker
Sunday, November 01, 2009 9:49 AM
As long as we talk about Sound we will continue to have a problem. We need to do something. We will never make everybody happy; when a rule is finally put in place some will think it is too much, others will think it is not enough, and yes, there are going to be those that cheat. There will be those that leave IMAC as they think the rule is unfair, but then we have had legislation in the past just as emotional and our numbers still hover about 1000-1100 members. Jim wrote above "What sound rule is going to be in place for the Muncie flying site?" Well? When the standard is set others will follow. When the standard is set and everybody is p*&^#) off I bet the numbers at the NATs will be the same. Me personally, something needs to be done nationally - just tell me what it is so I can comply.
Sunday, November 01, 2009 9:30 PM
I am 6170 with the 32-10, the 28.5 I have not tached.
Monday, November 02, 2009 3:38 PM
Tony: That's one wopper moter. Turning 32" anything at 6170 is ton's of power. Oh, I see now, 170 with RE-3s. Well that explains the 103-100 db readings on that prop. The tip speed chart above is accurate in your case. Max recommended RPM on 32" (per solid blue line on tip speed chart) is 5700. If there's anyone confused on how to read the tip speed chart above, let us know and I'll post directions. The chart will really help us all with our next prop purchase. Hope this helps, Dan Baker
Monday, November 02, 2009 10:14 PM
I know this is a really big issue in my region. For one we hear that mostly the SE region wants to go with 3 blade props and cans well in our tests that does little to nothing to fix the issue. Cost alone will force many to not be a part of IMAC. I understand that some fields have issue's with close proxmity to homes. But in our region all the fields I flew in this year (8) total. The locations were in unpopulated areas. Where sound was not a factor. Point is you have to address the issue where there is an issue. To force a change to the whole to help the few sounds govermental. Make changes to where they are needed and leave the rest as is. The CD should know what he will be dealing with and be able to apply said changes given the condition where they are flying.He then will be able to let everyone know what is needed in order to comply to the sound restrictions at that site. prior to the event.
Wednesday, November 04, 2009 6:36 PM
I agree with what has been posted and some of you were at the last Mocksville NC contest where I flew my plane with the DA200 and a 30X13. The chart is dead on regarding sound. I tried a 31X12 and constantly had an issue as to fly the plane at the speed I wanted was just inside the point where the tips would start to make noise. If you can manage throttle, then the 30" 2 blades will be fine. On another note: I would never run my plane wide open anywhere near level, so the GSL test is flawed as it requires you to run the plane wide open. I can tell you that my 200 will make the prop rip during the GSL test. It turns the 30X13 at 6510! So is this a good indicator for flight... not in my eyes. Good post! Glad to see the data come back!
Friday, November 06, 2009 7:44 AM
Has anyone even been to an event in the last couple years that preformed the ground sound level test? I haven't been to one in the NC region that had the gsl test in the past 4 years.
Friday, November 06, 2009 8:20 AM
Having measured last night: 30 x 13 Mezjlick = 29 & 3/16" long, pitch unverified 30x14 Biela = 29 & 5/16" long, pitch unverified 32x10 Mezjlick = 32" long I will try the Biela tomorrow come hell or high wind :) :) :)
Friday, November 06, 2009 8:21 AM
blade profiles very similar to from Mezjick to Biela. 30x13 Mez weighs 11 oz. 30x14 Biela weighs 12 oz.
Monday, November 09, 2009 6:57 AM
I think the industry needs to step up and give us a hand. Afterall its their financial livelyhood that is at risk if we loose our flying sites and have to change to electric pattern planes. There are two areas that could make a profound difference. Electronic RPM governers and more effective sound reducing exhaust systems...go to the "Flow Thru" web site and look at some of the noise cancelling resonance technology they use. Come on you experimentors out the there...our sites are in your hands/brains. Preston
Monday, November 09, 2009 6:46 PM
I have been IMAC'n for 2 seasons and even in that short period I have noticed many of the Unlimited pilots in my region switching to 2 blade setups due to a lack interest in the sound score...maybe, but I think partly it is due to the HUGE maneuvers in the Unlimited class Maybe, pilots will be able to give up a little power as The sequence committee works to make the sequences more compact. -chris sydor
Thursday, November 19, 2009 9:23 AM
I,m truly surprised that IMAC does not take a more responsable role in addressing the sound issue. I have attended IMAC events in our area where sound is an issue with neighbors but no special effort was made to control noise. There is another problem as well. At my home field, we have a sound limit of 95db @ 9 feet on grass. As a result, I use three blade props and effective sound reducing canisters in order to meet the requirement. I fly the same setup at the IMAC events and I have been dinged for sound by a few judges. I should add that I never have prop ripping issues with my setup. Prop ripping is likely the most offensive aspects to noise problems since it occurs up in the air and the noise carries a long way. I hope we don't wait to long before everyone is convenced that we will not have many places to fly if we don't act to get the noise issue under control.
Thursday, November 19, 2009 9:35 AM
There is another achievable way to address "power" requiremets and sound. If we were flying in described airspace (3-zone angled box set to 150 degrees), all matters of airplane design and performance would be reassessed (as a natural function of competitiveness) to maximize aircraft and sequence performance for the described airspace. Airspace management and allowable maneuver size have a close, but indirect correlation to inflight sound. Mandatory cans or pipes acting as a muffled exhaust has a close, but indirect impact on inflight sound. Passing a ground noise check has a close, but indirect correlation to in flight sound. Mandatory 3-blades would have a significant impact on inflight sound (although there is always an example of someone ripping a 3-blade). Finally it comes down to the pilot and the club and the IMAC rules. Not every field can or should host an IMAC contest. The clubs have to be the first line of defense for airfield retension. Also, I think it is perfectly acceptable for particular clubs to have "noise-waivers" on the contest sanction (for instance some fields may make cans mandatory). Pilots, clubs, and the IMAC rules all need to work together. Thanks, Jim
Saturday, December 05, 2009 2:14 PM
While we are doing our best to be as accomodating to our neighbors as possible we should be demanding this same kindness from the neighbors. Firstly, a standard of acceptable noise levels needs to be established. How about the sound of a Cessna sporting a 540 pulling a three blade at climb power at 800 ft. AGL?? This is a commonly heard sound around airports that no one complains about. Why don't we measure that sound and make sure we are typically less than those sound levels? Then, when the compaints come in, we have good reason to argue that it is unreasonable for our neighbors to demand complete silence in a world that seldom provides such comfort. Many neighbors would complain if the sound levels exceed that of a Texas mosquito at 50 feet. While we are trying to be silent, we also need to be very loud about demanding the same respect and tolerance afforded others in our community! Art Cloutier
Tuesday, December 08, 2009 10:55 AM
Unfortunately I don't think we are in a position to demand anything from our neighbors. I have never heard of an RC club complaining about a neighbor and causing them to lose their house. On the other hand, the complaining neighbor is responsible for many lost fields. It is to the benefit of the entire RC community in general, and giant scale fliers in particular, to keep our planes quiet.
Tuesday, December 15, 2009 1:43 PM
You can debate all you want to but the fact is, we are losing fields because of noise. This really is a fact. In my area alone, we have lost two (2) flying sites this year due to noise. Also, I beleive there are clubs that would entertain the idea of an IMAC event if it were not for the fact that it would put their site at risk.
Tuesday, December 29, 2009 12:19 AM
I don't care how quiet they get. The neighbors will always complain. It only takes ONE! Once the quiet issue is solved they will raise the safety issue, or the environmental issue, you name it and they'll complain about it. I call these people the 'Fun Cops'. Since we're in the rollover mode don't be surprised by the next attack on our fields.
|
|
|
|
|
|