Conference vmszoo::rc

    I am the head of the noise reduction committee for the Vaca Valley
    RC Club here in Fairfield, CA.  I will be real interested to read
    of results you come up with.
    
    The AMA is suggesting we work toward a 90db at 9 feet target.  I
    have talked to some AMA District people that believe this will be
    a requirement for having AMA insurance within two years so its a
    good idea to get a rough idea of where various prop/powerplant
    combinations are in relation to that target.
    
    In the for what its worth category, several things affect the reading
    you will get on your meter (Ihave one too).  I measure at 9 feet
    at a 90 degree angle to the head of the motor on the muffler side.
    I hold the meter about two feet to my side so that sound waves don't
    resonate off of me (the meter picks up noise from any direction.
    I measure downwind from the airplane.  Also you have to watch out
    for what is behind you, we have a shed with an overhang behind our
    pits, and with it at my back it increases the db reading from resonance
    off of the shed/overhang.  you will also get a different reading
    depending on the surface you measure from, a dirt or gras surface
    absorbs a couple of db.  I measure from asphalt.
    
    May I suggest that you include the following info in your results,
    I will post results as I get them too.
    
    Engine size/make, Prop diameter/pitch/make, muffler/stock or other,Air
    cleaner, Other - soft mount, modified prop etc.
                                              
    Looking forward to hearing your results.
    
    Will Beatty
    

        Re:< Note 821.3 by WR2FOR::BEATTY_WI >

        Will,
        
                That's great!    I am planning to follow exactly the same
        procedure as you,  with  one small exception:  namely that I have
        to measure off grass  because  that's  what the flying field has.
        Isn't the AMA requirement 9 METERS and not FEET?
        
                Poking my meter at different  things  I  am surprised how
        quiet 90DB is.  I think  its  going  to be a heck of a problem to
        get down to that level.
        
                I wonder what they will do about ducted fans.
        
        This is going to be interesting!
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    90 db is surprisingly quiet!  The really tough part is getting that
    last 2 or 3 db out to get the level at 90.  I have a sunshine hobbies
    sort-a-scale eindeckker with an OS 50 FSR.  I soft mounted the motor
    (lord mounts) put a bru line air cleaner on it, and added a macs
    tuned pipe muffler to it and got it at 93 db.  It took a lot of
    tinkering with the prop to bring it down to 90 db.  I finally wound
    up with a wooden 12/8 cut down to an 11/8 which got me just at 90
    db.  All of the planes I've tinkered with so far boil down to doing
    somthing with the prop to getthat last couple of db.  Have you ever
    tried any of the pattern type 11 or 12/18's?
    
    The distance to measure from is 9 feet.  I hold the meter about
    a foot off of the ground.  It's sunny and 60, I'm off to get some
    stick time.
    
    Will Beatty
    

        Re:< Note 821.5 by WR2FOR::BEATTY_WI >

                First test.   Measured on ice with about 1/4 inch snow on
        top.
        
        Lou Andrews Aeromaster, OS .91 FSR, 13x6 Master airscrew
                                                        101 DB
        Great Planes PT40, OS .40 FP, 10x6 Master Aurscrew
                                                         86 DB
        
                Incredible difference!   I  had  to go back and remeasure
        the Aeromaster after doing the PT 40.
        
        Anker

    Anker,

    Subjectively, how much quieter did the PT40 seem, over the
    Aeromaster ?

    Anker, That PT40 has a 10x7 prop.... I have an OS SF .40 and with
    a 10 x 7 prop, I get a BIG loss of RPM compared to the 10 x 6.
    
    
    						Dave
    

        Re:< Note 821.7 by LEDS::COHEN >

                At full  throttle  it was a heck of a lot quieter, but it
        didn't sound like the Aeromaster was 32 TIMES as noisy.
        
                We  did  some    new  measurements  on  grass  yesterday.
        Interestingly, the PT40 went  up by 2 DB, I had expected it to go
        down. I added a new plane:
        
        Great  Planes  PT-40,  O.S.      .40  FS,  Master  Airscrew  10x7
        (correction)                                            86 DB
        Scooter II, K&B .20 Sportster, Mater Airscrew 9x5
                                                                88 DB
        
        Anker

>                At full  throttle  it was a heck of a lot quieter, but it
>        didn't sound like the Aeromaster was 32 TIMES as noisy.

    DB, is of course, a log. scale, but the human ears' ability to
    perceive sound is only logrithmic over a relatively narrow range
    of sound levels, also the scale changes depending on the frequency
    of the sound.  The human ear perceives low frequency sound quite
    poorly at low volume levels, as compared to high freqs. at the
    same level, thats why most stereos have a loudness button to boost
    the bass at lower volumes, these loudness features typically are
    "contoured" so that as the volume knob goes up, the amount of bass
    boost goes down.  As sound level goes up, the ear gets to a point
    where the sound is no longer heard, but is instead perceived as
    pain (about 130DB), higher frequencies lower this pain threshold.

    I can't remember a lot about this stuff, but a few years ago I did
    some consulting about environmental sound control with my father.
    Maybe I'll go find a few of the books I bought around then, and
    see if I can find anything of related interest.

    Randy

    Anker,
    	Did the PT40/OS really sound quieter than the scooter/K&B20?
    I am really surprised by that.  By the way, MA had some article
    that said that some geared electrics are comming in at high
    sound levels.  So much for electric = quiet.  Vibration of the
    airframe and prop noise are probably the next thing to go after
    after a better muffler.  More pitch and less diameter seems to be
    the way the pattern guys are going.  The prop noise is really very
    noticeable with big 4-strokes.  I think that much of the noise comming
    from the Aeromaster is from the fuse vibrating.  It is a very noisy
    structure compared to something like a Super Sportster.
    
    Charlie
    

        Re:< Note 821.11 by LEDS::WATT >

        Charlie,
        
                My scooter  probably  isn't representative because one of
        the muffler screws  has  stripped  and there is a small amount of
        air leakage from the  connection  between  the  muffler  and  the
        header.  It will be  interesting  to  see  how much a new muffler
        helps.  I'm about to call  K&B for a new one, plus a new carb for
        my K&B .61.
        
                Bill's plane is probably quiet mainmy because of the high
        pitch prop - a 10x7 - which doesn't seem to impact anything other
        than acelleration on touch and go's.
        
                I am sure you are right about vibration causing  a lot of
        the  noise  from the Aeromaster.  I will order a  J'Tech  muffler
        today  and see how much it helps.  I also know  the  engine  will
        pull a 13x8 prop, by I lose vertical ecelleration.
        
                This is real fun.
        
                On  the  next  flying  site for the CRRC we will probably
        impose a  90  DB  noise  limit.   I believe we can get any normal
        engine under that level. I'm afraid the F16 will never comply.
        
        Anker

    Anker,
    	Did the PT40 have vibration isolation or standard wood mounts?
    Every one I have heard had lots of vibration but that was with the
    OS40FP engines.  The FP engines are poorly balanced in my opinion
    as they all vibrate more than the FSR's.  
    	I think that 90 DB in the near future is going to be a major
    enforcement problem and cause lots of bad feelings.  The measurement
    is quite variable and a plane might pass today but given slightly
    different running and weather conditions, it might fail.  I would
    suggest some sort of intermediate level that is easier for everyone
    to comply with.  That would still weed out the really noisy planes
    and not make everyone have problems with compliance.  I want to
    see a trend towards noise reduction but I don't want to see major
    panic. (No offense, Eric)  Until engine manufacturers start supplying
    decent mufflers and everyone starts using soft mounts and quieter
    prop sizes, it is going to be difficult and expensive for everyone
    to comply with 90DB.  Even if you get all of the best stuff, you
    may be marginal under certain conditions.  Unless the site is in
    a very critical noise area, I would hate to see this issue pushed
    all the way the first year.  Why not phase in the 90 DB in a couple
    of steps allowing technology and knowhow to evolve over a couple
    of seasons?
    
    Charlie
    

        Re:< Note 821.13 by LEDS::WATT >

        Charlie,
        
                If I  can  get  the  Aeromaster down to 90DB then I don't
        think there's any  excuse  for  regular sports planes.  I'll make
        the Aeromaster my test case  and probably not allow anybody to be
        noisier  than  it.   I know  it  will  require  some  investment:
        muffler, mounts, maybe a new prop.
        
                Let's see how it goes.
        
      
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        Re:< Note 821.13 by LEDS::WATT >

        Sorry Charlie, I forgot to answer your question,
        
                Bill hasn't done  anything out of the ordinary other than
        use a fairly large  prop.   The engine is mounted on the standard
        wood rails.  I was as surprised as you are.
        
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    Anker,
    	I would like to get envolved in your noise testing if you want
    help.  I have done lots of similar testing in the past and I want
    to increase my experience in noise reduction.  I think that much
    education will be required to get the non technical flyers (and
    there are lots of those in my club) to understand noise reduction.
    This would be a good topic for club meetings but most members never
    attend them.  Maybe a writeup of test results could go in the
    newsletter.  I've helped out some members of our club that haven't
    a clue how an engine works (torque, horsepower, prop selection,
    etc), how the RC equipment works, or how to properly mount this
    stuff in a plane.  I've seen a few articles published on noise
    testing but I know that the test conditions can greatly affect the
    results.  Duplicating the conditions carefully is the only way to
    get a fair comparison of noise levels.  If you have a level that
    is hard to achieve, this gets more critical since even a good setup
    may be borderline.  I think that the more technical modelers should
    lead the way to come up with simple, inexpensive solutions to noise
    reduction.  Also, manufacturers must start building quieter mufflers
    that are matched to their engines.  Many of the aftermarket mufflers
    aren't really designed for a particular engine's characteristics.
    They may be over or under designed for your particular engine. 
    Some add more weight than is necessary and may upset the exhaust
    tuning of your engine.  K & B is the only manufacturer that I know
    of that has come out with a line of quieter than usual engines.
    Too bad they aren't very good.  What is needed is OS quality with
    a muffler design like the K & B Sportster line.
    
    Charlie
    

    I think the answer to the PT40 is the oversized prop. I tried
    running an 11x7 on my 45FSR and it reduced the RPM by a LOT,
    so much that it seemed to be "lugging". I thought it was too
    much prop and went back down to a 10x6.5. A big prop on the
    40FP will reduce the RPM by so much that I'm not at all surprised
    about the noise reduction. I wonder what the power reduction
    is? As far as I'm concerned, that's not an acceptable solution
    to reducing noise.

    I agree with Charlie, you should have a period (say 1 year) of
    monitoring sound levels and helping people to be aware of noise
    and how to reduce it, before you start enforcing a limit. If
    you approach it as a joint effort of the club leaders and the
    members, rather than just imposing and enforcing a new
    restriction, I bet you'll wind up with fewer noise problems
    AND fewer disgruntled members.

    An easier way, I think, would be to let Charlie "borrow" your
    dB meter for a couple days, I'm sure we could help to calibrate
    it on our superb lab equipment so everybody's plane would fall
    below 90 dB!

    Dave

    I hate to say this but starting up front with a noise limit on a
    new field may be the only way to go. Even if it costs $$$$, which
    it will in my pocket also. The problem with many sights, and potential
    sights is people bitch'in about the noise to the point were the
    owner gets so many complaints that the easy way out is to SHUT
    THE FIELD DOWN. The major point made by the owner of a new possible
    CRRC field was noise, and neighbors complaining. To me I'd rather
    pay the penalties and fly than not have a place to fly at all.
    And that is what it's comming to these days. 90% of the club
    may have ships that conform to 90db or whatever, but it only takes
    one person flying at the wrong time day after day to ruin it for
    everybody... You have to draw the line somewhere, and I feel that
    imposing mandatory limits at a given field or fields is the way
    to go right from the start if noise could shut the field down.
    CMRCM is lucky, there more out of the way, and it appears fron the
    outside that noise complaints are few if any....
    
    
    
    					Dave
    

    Since I am flying choppers, I have several questions that require
    answers concerning how noise is measured, etc.  For example,
    how much does collective pitch change the noise level?  What about
    tail rotor pitch?  How do I measure as far as RPM is concerned?
    My guess would be that I would measure at just lift-off pitch
    and RPM, however, I can and often do change this between flights
    from the hover RPM and hover pitch trims on my transmitter.  Also,
    I am not sure how I could soft mount my engine in a chopper, since
    the clutch is hard mounted, but requires precise alignment with
    the engine.
    
    The other side of the coin, however, is that with the Schluter muffler
    that I am running, my choppers are both much quieter than several
    of the planes at our fields. I guess I will have to try to get a
    reading to see if I exceed the 90db mark or not.  I still have the
    questions as to how this would be measured.
    

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	/	__|___|__/  BREAK A BLADE,
			    Ken    	

        Charlie,
        
                I will  be  delighted  to involve you in my noise testing
        experiments.  Are  you coming to the meeting tonight?  If you are
        we can have a chat about how to proceed.
        
        Dave,
        
                My experience with oversize props is that on static tests
        they do mizerably, but in  the  air  under  speed its a different
        story, the prop unloads and the engine reaches peak RPM.
        
        
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re: < Note 821.20 by CURIE::ANKER "Anker Berg-Sonne" >
>        Dave,
>        
>                My experience with oversize props is that on static tests
>        they do mizerably, but in  the  air  under  speed its a different
>        story, the prop unloads and the engine reaches peak RPM.

    Ah, but then there is a hole in your procedure. If planes are
    measured only under static circumstances, then you may get
    a false reading. What we're really concerned about is the noise
    while the plane is flying, not on the ground.

    I believe my point is still valid: If we (I'm a member of CRRC
    too!) locate a field that has noise restrictions up front, we're
    asking for trouble. If that's all we can find, then we should go
    ahead and have the restrictions, but as Dave Hartwell said, all it
    takes is 1 or 2 turkeys to spoil it for everybody, and you can be
    sure that if we just open up a new field with new noise
    regulations that nobody has ever had to deal with before, and
    hasn't the foggiest idea how to deal with, you're going to have
    problems. Charlie said it: There are members that don't have any
    idea how their engine works, who would be expected to solve
    problems of resonances from many sources excited by many other
    sources? I don't think so. What, do we post a "noise police"
    member on site during all daylight hours? This has to be
    self-regulating to work. If the guys can't get the frequency pin
    board under control after all this time, how are we going to get
    noise under control? 

    Dave
        

    Boy,
    	It's nice to be having a discussion with Dave Hughes on my side
    for a change.  (We ususlly butt heads at work and enjoy flying
    together)  I think that moving in the direction of noise reduction
    is mandatory and getting a new field is an opportunity to emphasize
    noise reduction BUT it takes an adjustment period and the easy
    availability of the necessary equipment.  I bet if we get three
    dB meters and go to three different sites to do the measurements
    on a single plane that we will get nine different readings.  How
    do you set the engine during the test?  Do you scream it lean or
    set it on the rich side?  The difference isn't trivial.  Let's
    face facts - 90 Db at 9 Feet is not trivial for many forms of aircraft.
    Gliders may not have a problem but pattern ships with glass fuses
    and many trainers will not comply with out of the box equipment.
    I support Anker's testing approach to set some possible standards
    before arbitrairly setting a hard and fast limit.  By the way,
    all of us noters should lead the way in this since we have this
    tremendous wealth of knowledge and experience at our fingertips!
    
    Charlie
    
    

    Re .23
    
    My reference was not comparing the drop zone to CMRCM, as for isolation
    around these parts the drop zone is hard to beat. I was comparing
    the possible new field with the CMRCM.... 
    
    Let's put things another way... CRRC also has a very good chance
    of using a field in Medfield. It is also very isolated. There like
    the drop zone, noise most likely will never be an issue. I was one
    of the three that met with the owner of the possible new field (this
    makes for a possibility of 2) He was an extremely easy going person.
    The kind of person one does not run across everyday. He must have
    stated 5 or 6 times that night that his ONLY concern was noise and
    neighbors. Any fields are hard to come by these days with expensive
    land and development. I see nothing wrong with requiring aircraft
    to meet a certain noise level at a field of this type. If it means
    4 stroke only, then so be it. (I own no 4 strokes, nor can I really
    afford to buy one) At a minimum certain planes and perhaps that
    also means certain members are banned from the field. At the worst
    the owner say's "too many complaints, sorry guys but I have to shut
    you down". What's your preference?
    
     One must also be aware that perhaps flying louder planes during
    limited hours may be a possibility. In general unless you have
    some crank sitting home all day looking for an excuse to bitch,
    people only tend to complain most during early morning hours
    especially weekends, and at evening hours when their sitting on
    the porch at night relaxing reading the paper, watching the boob
    tube or whatever. 
    
     To make it work, everybody who fly's there needs to police the
    field. Up front before a key is issued you must read and sign a
    statement insuring that you understand the rules and regulations
    that apply to a given field. If you don't like it then you can't
    fly there, and you go to an alternate field or to another club.
    If enough people don't like it, then nobody flies there and at that
    point the club would most likely give it up.
    
    
     The biggest problem that I have seen with rules at fields such
    as frequency board is that you show up, say hi to a few people 
    which you probably don't know. Read any rules that may be posted,
    and try to figure out what to do. In general no one takes the time
    to explain to you how the rules and regulations tie together, let
    alone 3IM issues, how many up at one time, where to stand, etc.
    And then when you do something wrong, and you did'nt even know it
    nobody says anything to you, let alone explain how not to get yourself
    into that situation again.
    
    Sorry, I'm getting carried away!!!!! 
    
    
    						Dave
    
    Experiance is a wonderful thing................. It's something
    that all can benefit from........
    
    
    I'm sure that CRRC will not be the first club to address this issue
    and I'll bet that many clubs LOST their field because they failed
    to take decisive action..........
    

        Re: policing
        
                My proposal is inly to allow planes with a "certification
        sticker" attached use the new field.  To get a sticker one has to
        have the plane noise  tested.    In  the interest of fairness the
        tesating would have to be done with the same meter under the same
        conditions for all planes.  As the most probably person to do the
        certification  I  would  ensure  that  the  planes  really   were
        operating at close to peak efficiency.
        
                I know there are all kinds of ways to  "cheat".  Have the
        plane certified and pull the insert out of the muffler  -  change
        the  prop, etc.  etc..  The "solution" to this problem  would  be
        spot checking planes that seem excessively noisy.
        
                I am  going  to  research this issue agressively with the
        goal of having a noise policy in place from the beginning.
        
                Interesting point about props unloading and giving higher
        dynamic than static noise  levels.  Don't know how to handle that
        one.  Buzz the noise  meter  at exactly 9 feet and full throttle!
        :-)
        
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        Anker

re: < Note 821.26 by TARKIN::HARTWELL "Dave Hartwell" >
                      -< Sorry, I got carried away!!!!! >-

>    Re .23
>    
>    My reference was not comparing the drop zone to CMRCM, as for isolation
>    around these parts the drop zone is hard to beat. I was comparing
>    the possible new field with the CMRCM.... 

    Fair enough. My point, which probably got lost in the noise,
    is that CRRC members are used to an extremely isolated field,
    and most are unlikely to have ever given noise any consideration
    before. We're talking about a problem similar to the 1991 radio
    rules, and you know how much controversy THAT has stirred up with
    many years of notice. In this case, we're talking about guys who
    have airplanes they have been flying for years, that will be
    forced to make modifications, perhaps major modifications, to them
    to meet a new noise spec. That's going to be very hard to sell and
    very hard to enforce.

    re: .27,
    Here's another curve ball for you, Anker. Where will you do
    noise certification? At the noise-restricted field? Where will
    you help folks experiment to get the noise down? The only place
    it makes sense to do that is right where you want the noise to
    be restricted, at the field! I certainly can't experiment in
    my back yard - I ran-in an engine in my back yard a couple years
    ago and within about 10 minutes the cops were coming up the
    street. I shut it down quick and they didn't stop, but I'm not
    going to annoy my neighbors playing with my noise reduction
    experiments.

    Anker, I think that you do have a high probability of success
    because you are providing the key ingredient: Club leadership
    that is very actively trying to help the members to carry out
    the club's goals. As long as the leadership is active, and
    indeed bending over backwards to help, it's very likely to
    succeed.

    By the way, I got my Snuf'ler a few weeks ago and have it
    installed in my Kavalier and I'm anxious to try it out. But,
    I don't have the fortitude to go out in rain and fog and sleet
    like you, Anker, so I haven't tried it yet!

    Dave

                I did a lot of noise measurement over the weekend.  First
        a couple of observations.  Wind makes a lot of difference, mainly
        increasing the reading from  the wind whistling around the meter.
        Accurate readings can only be  taken  if  there is no more than a
        slight breeze.  I also discovered  that  the  meter should not be
        held pointing at the plane, but at right angles to it.
        
                The average 40 size plane with an  OS  40  FP  is  almost
        always 93 DB +/- 1DB.  Bill Clark's  PT40  became  a  lot noisier
        over the weekend.  I believe it was because  he leaned it out, he
        will  argue  its  because  the measurements are unpredictable.  I
        have definitely  learned  that  you have to deliberately lean out
        the engine when  taking  measurements.    I  have  seen 4 and 5DB
        increases in noise with a few clicks on the screw.
        
                Large four stroke engines  Saito  .80  and  O.S.   91 are
        quite noisy, 94 to 95 DB, but the noise generated by them is much
        less obnoxious then the two strokes.  .048 engines generate about
        93 DB, but boy, are they obnoxious.
        
                My O.S.  91 FSR still shares  the  top  spot with a Kadet
        Senior powered by a .60 engine at 101  DB.    The Kedet is really
        interesting because the owner had added an aftermuffler connected
        with  the  standard  muffler with a 16 inch length of  tube.    I
        believe a lot of the noise is caused by vibration in the airframe
        plus the tube acting as a tuned pipe.
        
                Just as I was about to leave yesterday Dave Hughes showed
        up with  Snuffler Muffler, which we did extensive tests on.  I'll
        let Dave report on them.
        
                The CRRC board  has decided to impose an initial limit of
        95DB, which will pass 90% os all existing planes, and then revise
        this limit as we gather more data.
        
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    I am disappointed that a random db noise limit has been decided
    on. The reason for noise limitations is to protect the new site;
    ie not annoy the nearest neighbors, about a half mile away. It seems
    to me that the first thing to do would be to have a couple of people
    station themselves at those houses, then have some models flown
    at the field. We could use cb radios to co-ordinate, and thus find
    out what can be heard and what it sounds like. The current process
    seems like technology in stead of good sense.

re: < Note 821.31 by CURIE::ANKER "Anker Berg-Sonne" >

    We did some limited experimenting with my OS .45FSR and Snuffler
    muffler. It was the first time I'd run the engine with the
    new muffler, and it was obvious to me right off that the
    exhaust noise was significantly subdued, and the predominant
    noise factor was now prop noise. It was a good reminder that
    noise comes from many sources, and when you take care of the
    loudest source, another one becomes the loudest source!

    I had a supply of various sizes of props, so we experimented
    with props, doing noise and thrust measurements (Anker, I'm
    terrible with names, I don't remember who the two other guys
    were that helped out with this).

    Anker took the noise measurements, and we put the plane on a
    piece of carpet for low rolling resistance for the thrust
    measurements. The plane weighed in at about 6.5 lbs with full
    10 oz fuel tank, Snuzzler muffler (adds a few oz) and extra
    servo for my streamer. I built it for ruggedness, not lightness!

    Here is the data:

    O.S. 45FSR with Snuffler muffler, with an extra 2" curved plastic
    tube (homemade exhaust diverter). After each change, we readjusted
    the mixture for peak rpm. 

    Prop       noise (dB)       thrust (lb)

    10x6.5       91.5             4.1
    (nylon)

    11x5         90.5             4.9
    (wood)

    11x7         89               4.3
    (wood)
    

    I was surprised at the thrust measurements. It seems I've been
    under-propped on this motor.

    We attempted to take RPM readings also, but had a little
    difficulty and they do not make sense (11x7 read higher than 11x5
    which is impossible given the measured thrust) so I didn't include
    them. 

    We also tried an air filter on the intake, but it had no effect
    on the noise (after we readjusted the needle valve to peak).

    The one flight I finally got around to taking was with the 11x7.
    Compared to the noise level I was used to, it sounded like I was
    at about half throttle for takeoff. However, it had plenty of
    power, and seemed to fly just as well as with the smaller, noisier
    prop. Subjectively, it was very noticably quieter than with the
    standard expansion muffler, and I guess that's the point: With a
    little work and small investment, you can get the noise down.
    According to Charlie Watt, there were no measurements below 90dB
    on Saturday, so maybe I can claim (for a moment, at least) to have
    the quietest glo-powered airplane in the club!

    A comment about the Snuffler - it leaked oil out both the front of
    the muffler (where I had to drill a hole for the bolt) and around
    the joint between the Snuffler and original muffler body; made
    quite a mess. They provided no gasket, and I had sealed it with
    silicone caulk. Last night I remounted the Snuffler, using some
    1/32" automotive gasket material and more silicone, including
    silicone around the front hole. I may fly it again today at
    lunchtime, if I do I'll let you know how that works. 

    Dave Hughes

    Report on today's flying:

    My oil leak repairs to the Snuffler seem to have worked well.
    When installing a Snuffler, be sure to make a gasket for it
    (it comes with a thick rubber gasket for mating to smaller
    mufflers, but the 45 was too big for it.

    I took a flight with the 11x7 and another with the 11x5. It
    was pretty windy, and the 11x5 did not have the same power
    to fight the gusts. I have a 10x7 I'm going to try next,
    and am ordering a 10x8 to try as well.

    The prop tip noise can now be clearly heard, it is at twice
    the motor rpm (the note is an octave higher, for you musicians).
    These are the square-tipped wood props. A shorter prop will
    reduce the tip speed and thus the noise.

    In addition, the vibrations in the wing and fuse are more
    apparent. That's where shock mounting the motor will help.

    Dave

    Interesting Dave, I have a Magnum 40 Pro in a telstar 25 I am currently
    flying running a 9X8 zinger prop. I wonder how this set up would
    fair with the sound meter?
    
    
    Tom

    Went flying from 9am to about 1pm today and had a chance to get
    my Db meter on some airplanes at the field.  Results are as follows:
    
    Db      Plane        Engine        Prop              Other
    
    102     PT-40        Royal 45      MA  10X6          Enya Muffler
    92      PT-40        Super Tigre 40MA  10X6          Stock Muff
    102     EZ-P51       Enya 90 4S    ??(opps)          Stock Muff
    94      AeroStar 40  Royal 45      Wood Zinger 10X6  Stock Muff
    98      Hammer 20    O.S.35        MA 9X6            Stock Muff
    98      Checkmate    YS 60         Wood Zinger 11X10 Cowled Tuned
                                                         Pipe
                                                         
    NOTE: All measurements were taken from asphalt with a Radio Shack
    Db meter at 9 feet from the plane, a 90 degree angle from the engine
    head.  MA means Master Airscrew, 4S means four stroke motor.  All
    examples above were stock mounted engines.
    
    I have been working on a prototype muffler for my wifes company
    and got some very pleasing results on the prototype this morning.
    
    Db     Plane         Motor        Prop            Other
    
    92     RPM 25L     os 25 FP      MA 9.5X6          Stock Muffler
    89     RPM 25L     OS 25 FP      MA 9.5X6          Snuffler (J'TEC)
    86     RPM 25L     OS 25 FP      MA 9.5X6          Prototype
    85     RPM 25L     OS 25 FP      Rev Up 11X6       Prototype
    
    I only got to put a tachometer on the last two measurements, as
    you can imagine the 11X6 was unacceptable at 8500 but the 9.5X6
    ran at a healthy 10,500 at 86Db!  This motor is mounted on wooden
    rails with no other noise reduction options in place.
    
    Regards,
    
    Will Beatty
    

    Run this all again with thrust measurements with these mufflers
    including the stock muffler. Then if you lose little power, or even
    gain more you have something to sell. It's easy to make an engine
    quiet, it's quite another to have it quiet and produce power.
    
    						Dave
    

    RE 821.40
    
    Would'nt RPM with a given propeller equate directly to thrust output?
    
    If the RPM goes down I would think the thrust would go down
    proportionatly.
    
    Will

    Got out to do some more flying and measuring this week end.
    
    DB       Plane        motor        prop            other
    99       Royal        O.S. 61      MAS 12X6        Home made muffler
             Stuka        SF w/pump
    95       Pilot        O.S. 25 VF   Rev Up 9X6      Mac's Pipe
             Supra Fly    Rear Exhaust                 13,800RPM's
    91       Pilot        O.S. 25 VF   Top Flite       Mac's Pipe
             Supra Fly    Rear Exhaust 9X8             10,500RPM's
    93       Sig Kadet    O.S. 40F     MAS 10X6        Stock Muffler
    101      Pica Duelist Royal 45     MAS 10X6        Stock Muffler
                          (A Pair)
    89       Bud Nosen    O.S. 28F     MAS 10X6        Lord Mounted
             Champ                                     Motor/Snuffler
    
    Till next time,
    
    Will Beatty

                Friday night I installed the Snuffler Muffler in the O.S.
        .91 FSR that  turns  the Aeromaster ballistic.  The Snuffler fits
        entirely inside the stock muffler and is held in place with three
        screws that need to be  tapped  into  the muffler.  The effect is
        that you get the chanbers interior  to  the Snuffler and two more
        chambers, one in front and the other  behind.    The  fit  of the
        Snuffler is almost perfect.
        
                Without the Snuffler installed the statistics were:
        
        O.S. .91 FSR, Master Airscrew 13x6: 101 DB, 11,800 RPM
        
                After installing the Snuffler I got:
        
        O.S. .91 FSR, Snuffler, Master Airscrew 13x6: 97 DB, 11,400 RPM
        
                Finally with a larger prop I got:
        
        O.S. .91 FSR, Snuffler, Master Airscrew 13x8: 94 DB, 9,800 RPM
        
                7 DB is a very significant reduction in noise.  It has to
        be heard to be believed.  From being at  the  pain  threshhold it
        now sounds almost like a four stroke.  Almost all of the noise is
        prop noise and not obnoxious at all.
        
                The  plane  has also become much more pleasurable to fly,
        even though  it  cannot fly vertically indefinitely with the high
        pitched prop.
        
                Next, I will experiment with soft mounts and an extention
        on the muffler.
        
                      _ 
                     / |
        |  _====____/==|
        |-/____________|
        |    |        o \
             O           \ 
                          O
         Hang in there! o_|_
                          |
             Anker      \_|_/

Extract from the Agenda for the March CIAM meeting.

< item 1.2 General Characteristics of Aeromodels..

< The following noise limit shall apply to all aeromodelling engine categories
< effective Jan 1 1991; 90db at 3 meters.

If it passes it will mean that all FAI class models will be limited to 90db at
3 meters. I have my doubts it will pass as it is written but something more
moderate will be passed next month.

The present F3A limit is 96db, to get pylon in its present form to that level is
going to be impossible, Helicopters are going to have a lot of work to do, and
Scale with the large engines are going to find it very hard.

I think the rule if passed will kill the following events in there present
form:-
	F3D Pylon, Free Flight F1C; Control Line F2A Speed, F2C Team race, and
	F2D Combat.

Any comment Tom T on getting F3A below 90db.?

John

    NOTE: 3 meters = 9 feet 10 inches. Anker - that should be your
    standard, not 9 feet!


    Dave

        Re:< Note 821.45 by LEDS::HUGHES "Dave Hughes (LEDS::HUGHES) NKS1-1/E3 291-7214" >

                The added  10  inches  will  make VERY little difference.
        You have to  double  the distance to get a 3DB reduction in sound
        level.
        
                      _ 
                     / |
        |  _====____/==|
        |-/____________|
        |    |        o \
             O           \ 
                          O
         Hang in there! o_|_
                          |
             Anker      \_|_/

RE:    < Note 821.46 by CURIE::ANKER "Anker Berg-Sonne" >

     >   You have to  double  the distance to get a 3DB reduction in sound
     >   level.

	Wouldn't doubling the distance reduce the sound by a factor of 4
	(or around 6DB)	instead of 2 (3DB) due to the inverse square law?

    Later,

    Don_who_only_remebers_a_little_of_his_college_acoustics

        Re:< Note 821.47 by SMART5::DHENRY "CRU80 - "A challenge to your musical knowledge"" >

>	Wouldn't doubling the distance reduce the sound by a factor of 4
>	(or around 6DB)	instead of 2 (3DB) due to the inverse square law?
        
                It doesn't  work  that way close to a reflective surface.
        Close to the  gound you actually see sound levels drop off almost
        linearly.

                      _ 
                     / |
        |  _====____/==|
        |-/____________|
        |    |        o \
             O           \ 
                          O
         Hang in there! o_|_
                          |
             Anker      \_|_/

    
    	You also didn't order the 2nd half of the noise reduction kit!
    Try converting your .25FSR to diesel.

re .51

I did get some info from Davis Diesel about their diesel conversions. I'd
be happy to let you look it over.

They have a lot of testimonials from satisfied customers. I'd consider it,
except for:
- cost of conversion
- cost of "cheap" fuel (the way it works is that they put a LOT of ether in
  the fuel to make it diesel, so it's cheap kerosene cut with 25% or more
  expensive ether). And try to store the stuff. 
- The mess (you think cleaning up after a 2-stroke is bad? Try the gunk you
  get out the back end of a diesel)
- I don't want my plane to smell like a bus
- If I want smoke trails, I want white, not black smoke.

Now, if I had a scale B52 it would look pretty authentic leaving behind a
thick cloud of black smoke...

    RE:  821.55
    I'm guessing that noise reduction gets a little more attention in
    Europe because of the population density.
    
    While this may not be a uniform problem in the USA, it is appropriate
    that we modelers pay attention before someone without an interest
    in or an understanding of our sport does!  Remember this is the country
    where airport expansion and landing patterns have been essentially
    decided by people opposed to the noise.
    
    I have to disagree with your comment on 90db being unreasonable.
    It is achievable with a surprisingly small effort.  96db is a snap
    and I don't believe its enough of a reduction to foster noise reduction
    efforts by the manufacturers in a way that will lead to nipping
    this problem before it becomes a crisis for us flyers.
    
    Quiet Flyer

    I've come to some intresting conclusions about noise lately. The
    main problem that I see with noise is with prop speed. The 2 cycle
    engines of current vintage like to rev high to make lots of power.
    With this high rpm comes NOISY props, exhaust noise and airframe
    noise is nothing compared to the prop. Case in point, I have a OS
    SF .40 engine with stock muffler. With a 10 x 6 prop it generates
    good thrust with moderate noise 94 db when measured. I have tried
    a Davis Desiel muffler, yep it's a bit quieter, but not much (Anker
    can I borrow your DB meter?) I even tried putting the Davis muffler
    in line with the stock, Slight noise reduction again. A 10 x 7
    prop really quiets things down but I loose a lot of thrust, and
    you can feel the loss in a big way. Things are much quieter due
    to slower prop revolutions, but this engine does not make it's
    power nor torque at this speed.  I installed a 24 inch exhaust
    extension, fitted with a 10 x 5 prop. In the lower RPM ranges it's
    pretty quiet, however now the engine really rev's at full throttle
    and it's terribly noisy. I hav'nt flown it yet but I held the plane
    verticle and loosy hld the plane. It may go verticle now, I can't
    wait to find out. According to the engine spec's it makes it's
    most power at 16,000 RPM. Yep, they are right, but it's noisy.
    Seems to me the manufactures could best solve the problem by designing
    a 2 cycle engine (No 4 cycle jab's please) that has a gear reduction
    unit built in. Then you could swing a longer heavily pitched blade
    at half the RPM. 
    
    I'm sure that by simply putting on a larger prop I could meet or
    come close to the 90 DB limit. However, the performance will stink.
    
    
    
    						Dave
    

    Dave, I don't think your attacking the problem correctly.
    
    If prop tip noise is what your now trying to reduce then you should
    go down in diameter rather than up. If your satisfied with the 10/6
    then I'd suggest purchasing every brand of prop you can find in
    the 9/8 size. Test each prop and determine what one seem best to
    you. Tip speed noise is a relationship of the tip going supersonic.
    I used to have a formula to figure this but can't remember it. I
    doubt however that your 10/6 at 12-14K is getting close to the
    supersonic range. You know you guys will find that a tuned pipe
    set long with higher pitched props greatly reduces noise. There
    isn't anything mysterious about pipes. They are quite simple.
    It's when your trying to ring every last rev out of a set up that
    you need to get really fine.  Tom

    A good average tip speed to hit on the the ground is 650 feet per
    second.  If you adjust your prop pitch and diameter to hit this
    speed you will get a good trade off between power and noise.
    
    Multiply the diameter in inches by 3.14 to get the circumference.  
    Divide your RPM's by 60 to get the RPMS per second.  Multiply the
    circumference by the RPMs per second.  Divide your answer by 12
    to get the feet per second rate.
    
    When you compare the results between different prop combinations
    the effect on tip speed is surprising:
    
                  O.S. 50
    
                  10500RPM w/ 12/6 = 550FPS
                  11200RPM w/ 11/7 = 537FPS
                  
    I have been experimenting with larger props cut down to 11 inches
    because it increases the blade or paddle area.  The O.S. 50 above
    pulls the airplane best with the 11/7 prop.  Some of the pattern
    drivers in my club are running 10/18's and 10/16's!  They are bringing
    their RPM's down but the vertical and speed performance is outstanding.
    
    I would be interested in hearing other noters results.
    
    Will    

    A little contrary to this, I installed a 10x5, in place of a 10x6
    the OS SF .40 not sure of the RPM but the engine was reving but
    it was much higher than the 10x6 and it IS NOISY. It made a big
    difference in verticle performance, and all around performance.
    Putting a 10x7 on this kills the RPM, NOISE, and performance in
    a big way... I guess all engines are different with their torque
    and horsepower curves. Sure would be nice to get a plot of these
    on the various engines.
    
    
    
    						Dave
    

RE: < Note 821.59 by WR2FOR::BEATTY_WI >

    GREAT!!  Since I don't usually have a calcualtor with me at the
    field, I took your formula one step further and reduced it down a
    bit so it will (hopefully) be easier to figure in my head while I'm
    at the field:

        RPM x d x Pi  ~   RPM x d    (RPM/1000) x d
        ------------  =   ------- =  --------------  = (RPM/1000) x d x 4.4
           60 * 12         229.18        0.23

    So, for a rough estiamte,

         (RPM / 1000) x diameter x 4.4  =  tip speed (in feet per second)


    Checking with the earlier examples;

        (10500 RPM / 1000) x 12 x 4.4 = 554.4 FPS  (Actually = 549.8 FPS)
        (11200 RPM / 1000) x 11 x 4.4 = 542.1 FPS  (Actually = 537.6 FPS)

    As you can see, my "estimate" is about 1% too high.  If you're
    really a purist, subtract 1% from your answer...  
    But then again, is your tachometer really accurate to 1% ?????

    I doubt anyone will remember to use this formula at the field, but I
    had fun doing it anyway...

    BTW - if you think it's hard to multiply by 4.4, try this: 
        multiply by 4, (save the number), divide by 10, add to first number

        Ex: 137 x 4 = 548       548 / 10 = 54.8     548 + 54.8 = 602.80


    OK, I've wandered far enough into the Twilight Zone for today...

                       _____
                      |     \
                      |      \                          Silent POWER!
      _        ___________    _________   |            Happy Landings!
     | \      |           |  |         |  |
     |--------|-  SANYO  + ]-|  ASTRO  |--|              - Dan Miner
     |_/      |___________|  |_________|  |
                      |       /           |     " The Earth needs more OZONE,
                      |      /                       not Caster Oil!! "    
                      |_____/

RE: < Note 821.60 by TARKIN::HARTWELL "Dave Hartwell" >

    This is not really contrary.  You are over loading the engine.

    If you tried a 9x7 or 9x8 or 9x9, then you would be increasing pitch
    without over loading the engine since you're also decreasing
    diameter...  And you would probably (?) get better performance than
    with the 10x5.

    I agree that the torque and horsepower curves would be the best way
    to determine the "best" prop for a plane.  

                       _____
                      |     \
                      |      \                          Silent POWER!
      _        ___________    _________   |            Happy Landings!
     | \      |           |  |         |  |
     |--------|-  SANYO  + ]-|  ASTRO  |--|              - Dan Miner
     |_/      |___________|  |_________|  |
                      |       /           |     " The Earth needs more OZONE,
                      |      /                       not Caster Oil!! "    
                      |_____/

    Its been a while since anyone touched this note.  Last week at our club
    meeting (NH Flying Eagles) we passed a new club rule to limit engine
    noise to 97 db.  This was prompted by several complaints from residents
    near our New Boston Field.  We elected to make this rule apply at both
    our fields, since our Merrimack Field is under town ordinance that sets
    97 db as the maximum level allowed.  No complaints have been made at
    the Merrimack Field, but we decided to be consistent in our rules.
    
    A committee was formad to begin the task of making noise measurements
    on our planes to see how well we can comply with this rule.  Last night
    was our first "noise checkout" date, and a total of 9 planes were
    measured.  No surprise that many of them failed the 97 db rule, and
    hence cannot fly at our fields until modified.  
    
    I won't go into the gory details of the specific measurements here. 
    The big offenders are OS46 SF with stock muffler at 98-99 db, and 
    Super Tiger 45 with stock muffler at 104db!  We tried swapping a 10x6
    APC prop for 10x6 Master Airscrew nylon, and found a fairly consistent
    drop of 3-4 db with the APC.  Quietest engine/muffler was a Super Tiger
    G40 with a muffled tuned pipe (sounds like a contradiction in terms)
    that measured 93 db.  I should also mention that a certain Gremlin
    running a stock OS 25 also came in at 93 db, sharing top honors, but
    jeepers, that's not a fair comparison ;-)
    
    More work is obviously needed to experiment with different props and
    mufflers, and the previous reports/experiments in this note will come 
    in handy.
    
    I'll make reports as we get more data and do more testing.
    
    Regards,
    Joe                                      

Complaints have put this on the Divot Digger's agenda for this month. We'll be
getting a sound meter and doing tests this summer. Cheap insurance to keep a 
field. Getting members to adhere to the rules when there isn't an officer at
the field is what I see as our biggest challenge.

Let's keep the discussion going as things develop

    Cautions
    
    Decide on a process to measure aircraft and stick to it.  Regardless
    of engine location/configuration.  It will give you a common ground for
    your analysis.
    
    Tom

    

NOISE
================================================================================

Preface:
    
    In the latest 1992 AMA Competition Rules Book, two,  RC flying categories
    have initiated precedent setting noise reform.     The two categories are
    pattern and helicopters.  Both have seen the need to initiate a reduction
    in the noise levels the aircraft emit.  This is only the beginning.

    For pattern, the noise level is measured from 3 meters  on the right side
    of the airframe.  The plane resting on the ground.    The meter 18" above
    the ground.  If on tar the noise reading must be 98db or lower.  On grass
    the readings must be 96db or lower.  

    For helicopters the reading is  96db or lower with the chopper in a hover
    1.5 meters above the ground.   The meter is positioned slightly down wind
    on the exhaust side of the chopper.

    Our club has decided to stay with the noise rule of 95db at 3 meters with
    the meter 18" off of the ground.
    
	From our past experiences and the many articles within the magazines,
NOISE, it's effects on the modelers and our neighbors,  has become ONE of, if
not THE, major factor, in the loss of RC flying sites.  It has become all too
apparent, that steps must  be  taken  in  order  to  meet the noise challenge 
HEAD ON!
	 It is common knowledge, that  the  noise problem  and  the solutions
are not a  simple process  of  eliminating ONE factor.   That is to say, that
there is not one culprit.    Rather, in  most  cases,  it is a combination of
factors that creates the problem.
	The NUMBER ONE factor contributing to the majority of the noise issue
with powered aircraft is the engines' stock muffler system.   This holds true
for the two stroke and the four stroke power plants.   The "stock muffler" is
nothing more than an "expansion chamber".    I, do not know of a single stock
muffler set-up that will meet our noise level requirements.   A stock muffler
on engines of .35 or larger alone just won't cut it at 95 db.    After coming 
to  the  realization that "STOCK", is not good enough, the next question is;

			"WHAT IS"?

From personal experience, the SoundMaster mufflers from Davis Diesel seem  to
work, along with the Snuffler from J-Tech.  I've also seen articles on rubber
bladders, home made mufflers and the like that are supposed to work.  I can't
vouch for their effectiveness.  I do know that Al Threasher has been using an
after market rubber bladder muffler  and  it  does  reduce the noise from his
engine set-up.
	The structure of the airframe, when,  caused to vibrate,  acts like a
speaker of a radio.    Different  structures  act  differently,  but they all
vibrate and cause noise.   This we can call the "speaker" effect.    The most 
common methods of reducing this effect  is the isolation  of  vibrations from
the engine to the structure of the airframe by using a " Soft Mount " system.
In most cases,  a  reduction of 1-3 DB can be attained by using a soft mount.
There are a number of systems available  on the market today along with a few 
home brewed ideas that seem to work equally well.
	Props, play a major role in the battle to reduce noise.    The shape,
materials, pitch,  diameter and flexibility all play  a  part in there noise
emissions.  The APC props seem to have gained an overall acceptance for it's
noise reducing effectiveness and it's efficiency.   However other brands can
and do produce acceptable results.    It's a matter of experimenting, to see
what prop make and size fits your specific application.      I cannot stress
enough the diameter and pitch part of the prop equation.    All to often, we



slap on a 10/6 to our favorite 40 sized engine and go bore holes in the sky.
A little experimenting with different diameters  and  pitches  will  yield a
better, more reliable and quieter running engine.  Key to noise reduction is
the efficient use of an engines RPM's.  In many cases this means running the
engine at  a  reduced RPM than  we  are  normally accustomed  too,  but it's
actually a more efficient use of the engines power.  Gone should be the days
of screaming an engine at  15,000  rpm's on the ground with a 10/6 up front.
You will find that running the engine down around  10,000 - 12,000 rpms with
sufficiently more pitch will improve an aircraft flight performance. 
	The last item  we  will cover  is  one  that  for the most part goes
unnoticed, the carburetor.    The venture of the carb with it's accelerating
air can lead to a high noise reading.      In most cases this is only 1-2 DB
but can prove to  be  that little extra you will need to quiet your favorite
bird down.    The common method  of  reducing the noise is the use of an air
filter.    There are a number of them on the market that work.      A porous
piece of foam can be stretched over the carb and held  on  with rubber bands
to make an effective cleaner.     Just make sure the foam is compatible with
the fuel you are using.     One side benefit  is  that the engine will see a
reduced amount of dirt particles.  This will extend the life of the engines.
Don't forget to periodically remove and clean the air filter.
	Remember that  it  is  a  combination  of  factors that leads  to  a
reduction in noise emissions.    The first being the exhaust system followed
by  prop selection  and  vibration isolation  then venture noise  and  other
airframe vibration.   Many  of  us have aircraft we've already built and are
flying.    It's  to late to install a vibration isolation soft engine mount,
OR IS IT?     Below is a home brewed method I learned from a fellow modeler.
It can be used to retrofitted an existing airframe.   It's also inexpensive.
I've used it a number of times, both as a retrofit  and  on  a new airframe.
Presently I'm using it to isolate an OS108. Try it,it works!

					Good Luck
							Tom


	1.	Remove the engine from the engine mount.
	2.	Remove engine mount from fuse.
	3.	Drill out bolt holes for mounting of engine mount to
		fuse to 1/4".
	4.	Cut four lengths of fuel tubing app. 1/8" longer than
		the thickness of the back of the engine mount.  These
		pieces will pass through the 1/4" holes and should
		protrude out app. 1/8"
	5.	Cut a rubber backer for the back of the engine mount.
		Make sure the material you use isn't effected by the
		glow fuel.  We've been using some foam PVC rubber.
	6.	Slip a metal washer onto one of the engine mount, mounting
		bolts. Slide a length of fuel tubing onto the bolt. 
		Push this into the engine mount. Repeat for the other
		three bolts. 
	7.	Now slide the rubber backer over the bolts and adjacent
		to the rear of the engine mount.
	8.	Apply a little Loctite(or similar) thread lock to the
		engine mount, mounting bolts. 
	9.	Position the assembly against the firewall and screw the
		bolts into the captive "T" nuts. Tighten this down until
		the fuel tubing and the rubber backing become slightly 
		deformed.
	10.	Reinstall the engine to the engine mount.  If there is 
		no cowl you can use the same engine mounting holes without
		any significant change in CG.