Conference vmszoo::rc

	Having virtually (ie I haven't quite decided) settled on 
	a Zlin 50L as the home for my newly aquired OS90FSR, and
	wanting to make the finished plane look really neat, it
	looks like I'm goin' to have to make a manifold and silencer
	for it...

	Has anybody made their own silencer, what sort of volume should
	it be, diameter of outlet pipe so as not to lose to much
	power, but still be reasonably quiet....
         
	A home made silencer would make it easier to incorporate a
	good smoke system. It seems that if the smoke stuff is warmed
	up, possibly by running it through pipe wrapped round the
	silencer, before it is injected into to exhaust, you get 
	much more smoke....

			cough bob

    BOB,
    
    Can't offer anthing around making yer' own muffler, but as to the
    smoke system; it's common practice to pre-heat the smoke mixture
    to get it close to its flash-point just before injecting it into
    the hot exhaust.
    
    However, this is normally done by pumping the mixture through several
    turns of coiled copper tubing "INSIDE" the muffler/manifold, not
    outside.  Can't offer much more as I've never, personally, installed
    a smoke system but I've seen lots of `em and I do know the "pre-
    heating" takes place within the muffler/manifold.
    
    You might want to try to obtain a smoke system kit such as the one(s)
    marketed stateside by Harry Higley or J-Tec (John Tatone) as these
    come with switching valves, check valves and other necessary
    components. 
    
    Adios,	Al

    In the book " 400 RC modeling tips" they have several ideas on the
    subject.  One that comes to mind is to use an old case from an aluminum
    majic marker.
    
    _________________________
    |  _______               \_______
    | 0|_____|0               _______|
    |________________________/
    
    
    Also, Epoxies let lose when heated.  A friend of mine tryed JB Weld
    on a broken Muffler flange.  Looked and held great until the engine
    ran for 15 sec. and heated up.  Then it let loose.
    
    Note:  Mufflers (stock) can be had in the $10-20 ($15 average) range.
    Most mail order houses carry them (Hobby Shack, Tower, etc...).
    My buddy got his for $10.95 for a Thunder Tiger .45.  Its worth
    looking into since most have toll free info. numbers.
    
    Chris
    

    Well, to take .1 a little farther...
    
    Why not use mechanical means to attach the exhaust extension to
    the pipe??
    
    Looking at it from the top
    
      Drill holes here
        1     1
     ___|_____|_______________
     |                        \_______
     |  2     2                _______|  (The magic marker...)
     |__|_____|_______________/
     

      ==========
      =        =
      =        =       Extension piece, need to mill this
      ==========
    
        Engine
    
    At this point, you take 2 small sheet metal screws and feed them
    through holes "1" and into holes "2"  (holes 2 will have to be smaller
    than holes "1").  Place a little bit of silicon on the end of the
    extension to make a gasket. Stick a screwdriver through holes "1" and 
    tighten screws into extension.  Then, take 2 larger, short sheet
    metal screws and screw them into holes "1".
    
    Presumably, you have machined the extension piece to accept the
    screw holes from the engine.  After the silicon dries you are ready
    to attach.
    
    From the looks of the Granite State Muffler, this is all that they
    did...
    
    Cheers,
    jeff
    
    (But wouldn't it be easier and cheaper just to buy 2 new engines??)
    

    Jeff,
    
    I did'nt think of the extension idea, but you're on target.  Dubro
    makes a 6 inch extension that you cut/tap as needed.  Also, mounting
    will depend on engine, i.e. do screws thread thru muffler into motor
    or thru motor into muffler?
    
    Chris

    
    One set of screws (permanent) go through muffler into extension.
    Another set usually go through mounting holes or strap around the
    engine into the extension.
    
    Is that what you were asking??
    
    Cheers,
    jeff
    

I've been tossing this around some more.  I think I'll bite the
bullet and go for an aluminum muffler, with high temperature
aluminum brazing.  This will be all new stuff to me, but I think
its the best answer for what I want.  I'm thinking that for
scale, I'll be fooling with muffler modifications anyway, so I
might as well learn (Al, you've been unusually silent in this
one). 

I would like to build a down exhaust type, or one where the
muffler is behind the engine -- a la K&B .25 (is that the one?).
In addition to the standard type.  Anyway, when I learn
something, I'll pass it on.

    John,
    
    I've been quiet for a very simple reason...I've never made a muffler
    in my life!  I've always used or made simple adaptations to what
    was/is commercially available.
    
    For the custom setup [live exhaust stacks fed from a single header
    on the engine] used on the MiG-3, I merely drew up what I wanted
    and [the late] Jim Leonard of Slimline Mufflers made up the whole
    enchilada for me out of brazed aluminum tubing.  The next time I
    need some unique setup, however, I'll doubtless have to do it myself
    unless Jim's son [who's now running the business] is as accomodating
    as Jim was and will fabricate for me from my drawings. 
    
    Adios,	Al

    Anyone,
    	I saw it mentioned that mufflers could be made from aluminum
    brazed together.  Is this done with standard brass brazing rods?
    I need to make a more effective muffler for my Cap 21 to keep from
    creating a noise problem.  I currently have a Slimline Pitts style
    muffler on my ST61.  It's much too loud.  I am thinking of making
    an expansion chamber to mount under the current pitts muffler.
    I have done some brazing with my arc welding rig, but I have never
    tried brazing aluminum.  If anyone has tried brazing aluminum, I
    would like to know how to do it.
    
    THanks,
    	Charlie
    

So far, I've found out this much.  You braze with aluminum
brazing rod and a propane torch (or oxy-acetylene).  There are
two prerequisites for a successful joint: the joint must be very
clean, and you never play the flame on the rod.  According to the
article I read, you heat the area of the joint, then apply the
rod so the metal flows in.  I suspect that the two parts must fit
closely.  There is a special flux for aluminum.  I'll pass on
more as I find it out.  Probably be after the first of the year
before I get the stuff and try it out. 

I have done a bit of aluminum brazing/hard soldering. You are correct John in 
saying everything has to be clean, it also has to be free of any oxide (ie. 
shiny not tarnished). The gap filling qualities are good so an exact fit is 
not critical but desirable.

For best results use a straight propane gas torch not Oxy-acetylene as the 
acetylene is rather dirty. The flux is a U-tektick (sp) alloy flux, it looks 
very similar to heavy grade oil. The flux must be liberally spread over the 
joint to exclude air. Gently heat and apply the rod to make the joint.

Don't quench the job immediately, let it cool for a while. Clean the joint and 
inspect for quality, if all looks good I generally anneal the job to remove 
stress. This is done by rubbing soap on a few strategic places over the job. 
Next gently heat the job until the soap marks turn a honey brown, remove the 
heat and allow to cool. Finally polish with steel wool and admire the result.

John

Thank You! That one will go in my muffler file for sure.  Please
bear with me John; I want to get this exact, because of the money
involved.  When you say propane torch, do you mean the common
garden varitey torch that you by from say, Bernz-o-Matic (or
whatever they have in Oz), that uses disposable bottles you can
buy anywhere?  If so, any special recommendations on tip sizes?
Finally, is the process as straightforward as you described?

I know that aluminum is a real stinker to join, primarily because
it oxides quickly, and must be very clean.   When I painted the
boat mast with Imron that I've referred to elsewhere I spent
quite a while with some very nasty acid chemicals etching the
surface for preparation.  An article I read recently talked about
using epoxies on aluminum and stressed the cleanliness of the
material. They recommended that you soak it in an acid solution,
of which a primary ingredient is sulphuric acid heated to 150
degrees for 10 minutes before bonding.  No thanks, Jack! 

I must admit though, both with the mast and with some small
alodine jobs that I've done, when its right, its very right.

Yes John I use just an ordinary Propane/Air torch, it sounds like the 
Bernz-o-Matic you describe. Mine is made by a company called Companion and has 
rechargeable cylinders. 

The tip size you require will depend on the size of the job, I use the smallest 
supplied with my torch for pipes and mufflers, it measures about 3/8" OD.

The flux I described excludes air while the joining is in progress so if you 
start with a clean joint you should have no problems.

John.

    Er, a muffler is more than an expansion chamber- it has to smooth
    out the pressure pulses coming in from the exhaust port.  Merely
    passing them along will NOT work.  Commercial designs that try to
    just be expansion chambers in general don't work, either.  
    	
    Here's a classic design- stolen from Hiram Maxim:
    
    	
         -----------------------------------------
         |    |    |    |    |    |    |    |    |
    -----     |    |    |    |    |    |    |    ------
    in 					        	out
    -----     |    |    |    |    |    |    |    ------
    	 |    |    |    |    |    |    |    |    |
    	 -----------------------------------------
                (cross-section)                            
    
    This is the original Maxim Silencer - as effective on a pistol as
    it is on an internal-combustion engine.  That is to say, can be
    pretty good.  It works even better if the holes down the middle
    are NOT aligned with each other, but are offset. (that is, provided
    you don't try to shoot down it!)             
    
    However, it's going to be rather complex to fabricate, because of all
    of those internal partitions.  A second way is the two perforated tube
    method, this is the standard for automotive mufflers: 
    	                                                 
    
    	-------------------------------------------
        |                                         |
    --------- -- -- -- -- -- -- -- -- -- -- ---	  |
      in -->                                  |   |
    --------- -- -- -- -- -- -- -- -- -- -- ---   |
        |                                         |
    ---------- -- -- -- -- -- -- -- -- -- -- --   |
      <--out                                  |   |
    -------- -- -- -- -- -- -- -- -- -- -- -- -   |
        |-----------------------------------------|
                                                     
    
    Both tubes are drilled many times with a small bit (in commercial
    production, the holes are punched).  The holes should NOT be in regular
    lines, rather, they should be scattered. Automotive design uses roughly
    2" tubes and 1/8" holes, you should scale accordingly.  
    
    This design is easy to make from tube and a bit of sheet.
    The inside tubes themselves only need to have about the cross-sectional
    area of your engine port or smaller.  Car mufflers of this design
    usually have either the IN or the OUT line "folded" so that they are on
    opposite ends of the outside canister- but INTERNALLY the exhaust
    gas route should vary greatly in distance but not in resistance.
    This distance variance spreads out the pressure pulses and smooths
    them.
    
    I have heard of the following design- also ascribed
    to Hiram Maxim. Here the idea is that the pressure pulses cause
    the gas to rotate in the flat (pancake-shaped) chamber.  Faster
    moving, higher pressure gas is prevented from exiting through the
    middle hole by centrifugal force until friction slows the gas down.
    	
    	
    ---------------------------------------________
       --> in                                      ------
    -----------------------------                        ---    Circular
                              /                             \    "pancake"
                            /                                 \   chamber
                          /                                     \
                         /                                       \
                        |                   ---                   |
    			|		   /out\		  |
                        |                  \   /                  |
                         \                  ---                  /
                          \                                     /
                            \                                 /
                              \                             /
                               ------                 ------
                                      ---_________---- 
                                                                   
    
                                             
    Go ahead and build a few.  You might learn something interesting.
    Besides, who knows when you might decide that your next super-scale
    ship has a nice place for a muffler- but no stock muffler fits.
    Custom time!  Besides, brass looks so nice.
    	
    Let us know how your experiments turn out.
    
                                                                         

Thanks for the input.  This weekend I visited the local tool
outlets looking at propane torches.  I did find out that aluminum
rod melts at 700 degrees,  so a regular propane torch should
work.

I've been boggled by the choices in the field.  It seems that if
you want a pencil flame (the smallest) you can get a garden
variety torch.  But if you want a hot flame, you can't buy one
with the pencil tip.  The swirl flame types are hotter than the
garden variety, and some are MAPP gas convertible.  Since I want
the option of brazing, I believe I'll go for a swirl flame type,
but there are other choices in there, all mutually exclusive;
automatic lighting, separate bottle and torch handle, automatic
gas regulator (I like this feature), and a couple of others.
I'll be entering an inquiry in the TOOLS file to help me sort out
all the info.

On the muffler design notes.  I think that a box with a pipe will
be my first effort, but I plan on doing something more.  Thanks
to your note, I'll be looking for a metal sphere to play with!  I
have a K&B .20 and one of the things I will do is to take apart
the muffler.  I think its simply a single tube with holes in it,
but its very effective.  I can do some rather intricate metal
work, since I used to play with clocks and watches, so most of
the construction techniques will be available to me to use.  I've
even found an amateur machine shop that can do milling! 

    Metal sphere?  I hope you mean to use it as an expansion chamber,
    not in the third design (Maxim vortex chamber).  The vortex chamber
    should be flat, no thicker than the input tube.  It's not a sphere.
    
    Maybe a sphere would look better, but I don't know if it will muffle.
                   
    Go ahead and try the experiment.  There's nothing like experimental
    verification.  (Willlbuuuurrr, ah told ya the rudder shoulda be in
    the tayell!)
    
    
    -------------------------
    
    Radio Shack sells a cheap ( ~ 20$ ) sound level meter.  It seems
    moderately accurate.  I have one.  Might be worth getting for a
    club that's worried about noise.
    
    Borrowing mine (for eastern MA residents) might be arrangeable.
    

Yeah, it was a case of having my head up and locked.  I saw the
circle diagram you made (great job) and remembered the spherical
mufflers I've seen on small engines.  OK, so I'll try both
techniques.

I'm getting some great feedback in the TOOLS conference, and will
post some info as soon as the topic starts wearing down.

Here's the info I got from the TOOLS conference.  I'll be getting
started on this as soon as our garage becomes habitable.  Right
now, the snow that's on the cars doesn't melt overnight -- but
then, most of you are well acquainted with that one!  This reply
stops at the fourth response because after that the discussion
went to jeweler's torches for fine work.

               <<< DELNI::WORK$01:[NOTES$LIBRARY]TOOLS.NOTE;1 >>>
                          -< Tools and Handy Gadgets >-
================================================================================
Note 473.0                       PROPANE TORCHES                      11 replies
CLOSUS::TAVARES "John--Stay low, keep moving"        40 lines  21-DEC-1987 11:37
--------------------------------------------------------------------------------

I'd like some advice about propane torches.  I want to build a
muffler or two for model airplane engines.  To do this, I need to
braze aluminum.  As I understand it, the aluminum rod melts at
700 deg, so an ordinary torch should do the job.  But, I figure,
while I'm at it, I might as well get the most for my money.  So
I'd like to be able to do simple brazing too.  Looking over the
products on the market gives mind boggling choices; this is why I
need the following questions answered (and of course, any advice
you care to add).

1.  It seems that many of the choices are mutually exclusive,
such as you cannot use a pencil flame head on a torch designed
for higher temperatures, such as a swirl flame torch, or one that
is convertible to MAPP gas.  Since I would like the brazing
capability, I assume that I cannot use these small heads.  Yet,
I've seen the heads offered individually, such as those by
Turner.  How hard is it to bolt up a smaller head, knowing that I
will have restrictions on its usage?  What are the risks?

2.  One of the attractive features is the Bernzomatic automatic
regulator. Its supposed to compensate for the drop-off in
pressure in the bottle -- is this feature worth it?

3.  Another interesting feature is self ignition.  I can see that
if nothing else, it would possibly save fuel.  Comments?

4.  One other option that seems tempting is a Bernzomatic model
that has the head separate from the bottle (there is a hose).
But you cannot get this one with the automatic regulator.  Is
this feature worthwhile?

5.  Back to the flame heads.  I'm really wondering if a pencil
flame is all that important.  I think that I can do the mufflers
with the standard head.  Comments on doing small work with a
standard flame head?  Is the swirl flame head hot enough to do
small brazing jobs?  Or do I need MAPP gas -- What are the
advantages of MAPP gas?

Thanks for any advice you can hand out -- buying a simple torch
is not simple!
================================================================================
Note 473.1                       PROPANE TORCHES                         1 of 11
AUTHOR::WELLCOME "Steve Wellcome (Maynard)"          59 lines  21-DEC-1987 15:20
--------------------------------------------------------------------------------

    I have never been successful in joining aluminum, so perhaps
    I'm not a good person to answer this one, but I will try.
    Well, in the first place you can't braze aluminum, if you
    go by the accepted definition of "brazing" (over 800 degrees).
    but whatever you want to do, how do you do it:
    Aluminum is a colossal pain to do anything with for two
    reasons:
    	1.  It oxidizes just about instantaneously when exposed
    	    to air, so for all practical purposes it always has 
    	    an oxide film on it that interferes with soldering.
    	2.  Aluminum melts at roughly the same temperature as 
    	    aluminum solder, so just about the time the solder
    	    begins to melt the work will too.  Practice on scrap first.
    I suspect for working with aluminum you'll want the softest,
    gentlest flame you can get that will heat the work sufficiently.
    An ordinary torch should be fine.  You might need a pencil flame
    to localize the heat though, I don't know how large these mufflers
    are that you are talking about.  Size of work has a lot to do
    with how large a torch you need.
    I suspect that MAPP would be way too hot to control.  The advantage
    (in most situations) of MAPP is that is gives a much hotter flame
    than propane, but for aluminum you don't need or want that extra
    heat.
    I don't believe you need an automatic regulator.  You'll only be
    working for a couple of minutes at a time at most, in all probability, 
    and the pressure won't change enough in that time to notice.
    The self-ignition might be nice, but I have one of the separate
    flint lighters for torches and it works fine.  The built-in
    ignitor would mean that you wouldn't be able to misplace the
    lighter, but that's about it.  A minor convenience.
    The separate head with a hose might be nice.  It would mean 
    that you could keep the bottle upright at all times, while moving
    the head to any position you wanted.  I have found that tipping
    the bottle to some strange inverted positions sometimes causes
    problems in the way the flame burns, but this has never been much
    of a hinderance.
    
    Now, for brazing (by definition, over 800 degrees) of steel,
    you need quite a bit more heating capacity.  Typical brazing rod
    and silver solder melt at 1200 degrees up to 1500 degrees, depending.
    You can braze small work (up to perhaps 1/2" square steel)
    successfully with a normal propane torch, slightly larger with 
    one of the "swirl" jobs, even larger with a MAPP torch.  One
    feature/problem I found with the "swirl" torch I have: it can
    either be off or full on, there is no in-between.  Although the
    valve can be adjusted for a partial flame, it doesn't burn properly,
    the torch head begins to glow red-hot, and in general it's not
    a good thing to do.  So, I've found the "swirl" torch to be of
    limited usefulness.  Perhaps there are better designs than the
    one I have.
    I don't have a MAPP torch, but if you want *HEAT*, that would be
    the way to go.  
    All in all, for your aluminum work I'd recommend an ordinary
    propane torch, possibly with a pencil flame if the work you're
    doing is small, but you can probably get by with the "normal"
    head if you take it easy.
    Keep in mind, all this from somebody who has never soldered 
    aluminum....
    
================================================================================
Note 473.2                       PROPANE TORCHES                         2 of 11
WFOVX3::KOEHLER "Who needs snow tires?"              20 lines  22-DEC-1987 08:38
                       -< here is my two cents worth.. >-
--------------------------------------------------------------------------------

    John, since you want to build custom tanks of aluminum you might
    want to start with a complete propane torch kit (one that has several
    tips). You will need different tips for different applications.
    As far as the torch welding aluminum.......oooowwww it's an ART.
    Going to a local welding supply store will enlighten you about 
    the different types of rod that are available. There is a aluminum
    rod the is made for the home handyman that is a low temp type. I
    have seen it used with a propane torch to fix holes in beer cans,
    (if that's what you like to do) There is rod that propane won't
    melt also. It is used with a oxy-act torch. Mostly this is used
    to weld thicker sheets of al. 
    If I can find the info on the low temp rod I will mail you a copy
    and you can order some if it is not available locally. At a local
    swap meet there is usually a demo of this stuff. I'll be going to
    a swap meet in Jan. if I can't find my info. I'll get it than.
    
                                       
    contact me off line and I'll help if I can with any welding problems.
    
    The Mad Weldor....Jim
================================================================================
Note 473.3                       PROPANE TORCHES                         3 of 11
NYJOPS::BOBA "Bob Aldea @PCO"                        15 lines  22-DEC-1987 09:33
                            -< Go for the hose... >-
--------------------------------------------------------------------------------

    I'm another one who has never successfully put a torch to aluminum.
    At this point I don't even try anymore.
    
    I do alot of silver and gold soldering, and occasional light brazing
    with an acetylene and air torch.  Its the same rig used by plumbers and
    some jewelers.  The biggest reason I upgraded from my propane torch
    is flame regulation.  As you tilt a propane torch, the flame output
    can vary radically.  When you are just reaching the flow temperature
    of hard solder, the result can reduce a piece of jewelry to a shapeless
    lump.
    
    Particularly if you plan to do light work related to modeling, I'd
    recommend the torch with the hose.  I believe they also include
    a belt clip to ease working overhead, and assorted tips will give you
    some flexibility.
================================================================================
Note 473.4                       PROPANE TORCHES                         4 of 11
BSS::TAVARES "John--Stay low, keep moving"           49 lines  22-DEC-1987 11:20
--------------------------------------------------------------------------------

Thanks for the offer Jim; if I run into the kind of trouble I'm
anticipating I'll ask you for sure.  I'll get back with the
results of all this if nothing else. 

I guess I assumed that everyone knew what a model engine muffler
looks like!  Dumb.  OK, so its no more than about 6 inches long,
and about an inch or so in diameter, shaped somewhat like a
cigar, with an inlet pipe that bolts to the engine and an outlet
pipe.  What's inside can vary from over a dozen parts to nothing.

I think that I can get away with the low temperature aluminum
solder (thanks for correcting this .1); the stuff with a 700 deg
melting point.  I don't anticipate over 500 degrees on the
muffler, since automotive hi-temp paint is for 500 deg.  Any
thoughts on how hot it gets?  I've heard of building the mufflers
out of STA-BRITE and brass, so I think its all OK.  As to the art
-- well, I'm gonna give it the college try anyhow.  Seems to be a
larger problem than I anticipated, given the experiences here. 

The primary material I will use is .050 aluminum, though I will
have to use small (1 1/2 inch x 1/2 inch nominal) pieces of 1/8
aluminum too.  Also I will use pieces of 1/4 to 1/2 inch tube to
fit inside the muffler. 

Yeah, at this time I'm inclined to the separate hose torch.  This
is one of those nasty tradeoffs I was talking about.  The
separate hose comes in two models; one has the pencil flame
(which I haven't found locally), and the other has the swirl
flame type head, and is convertible for MAPP gas.  Also, the
regulator model does not come in the hose type, and only with the
swirl flame head...Dear me, what shall I do, what shall  I do???
Sounds like the regulator is a nice feature.  The box talks about
a dropoff in pressure as the tank is used -- I know that this is
a bad analogy, but for the airbrush type tanks, it makes them
worthless.   I'd hate to get in the middle of the job and have
the thing start flaring or the flame drop off to ineffective.

Its like those manufacturers hired some marketing type to
purposely juggle tradeoffs so people would have to buy several
torches!

Based on what you've told me, my inclination is to buy a pencil
flame model for this job.  Later, if the need arises, I can get
the one convertible for MAPP gas.  I tend to stay with
small-sized projects, so I think I will even be able to braze
with the pencil flame, or with the standard tip that bolts to it.
I thought I saw some brazing rod that melted at 1200-15000 deg --
isn't this within the capabilities of a standard torch on small
jobs?  In other words, I will have no need for the hotter flame. 

    I don't think that you will have a problem with exhaust temperature
    on a 2-stroke melting your solder, but you might with a 4-stroke.
    The exhaust on a 4-stroke is much hotter.  I have seen the exhaust
    pipe char balsa where it was touching or almost touching it.  I
    am interested in what you are learning about working with Aluminum.
    I too need to make a custom muffler or expansion chamber, but I
    am aware that Aluminum is a Bitch to solder.  One other option might
    be to get everything set up and pay someone to heliarc it for you.
    Heliarc is one way to beat the oxidation problem and get good aluminum
    welds.  That's how they do welding on aluminum cylinder heads.
    
    Charlie
    

To the person that sent me some info on mufflers from Sport
Aviation magazine -- thanks.  I couldn't make out your name from
the signature.  I'll pass the information on to Brian Jorgenson
and anyone else who wants it.

    Geeeezzzz John! I think I sent that to you.  Did it have a yellow
    "sticky" on it?? 
    
    I'm almost finished my muffler, and I'll let you know how it works when
    I give it a whirl.  I used the Sears aluminum solder on some of it, and 
    a MIG welder on other parts.  The solder was VERY tricky to use!  I'll
    give a "full" report when I get more time.
    
    /Brian
    

Yes, it did have a yellow sticky.  Thanks for sending it along,
and thanks for adding the term yellow sticky to my vocabulary.

On homemade mufflers.  Glad to hear that you've got one going.
I sent a letter to Clarence Lee in RCM last week asking about the
availability of a commercial muffler for my Supertigre .15.  But
I still want to build one, even if I buy the first muffler.  So,
I'm still interested.

First chance you get, could you talk about the torch you're
using, and what is tricky about aluminum soldering?  I assume
you're using the 700 degree stuff? 

                                                   IN 

  
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Well John, although this is be no means drawn to scale, it represents the
basic design of the muffler that I constructed.  It has three chambers.  Each
chamber is approximately 1/3 larger than the previous chamber, permitting the
gasses to expand slowly.  The Aluminum pipe I used for the outside 
construction was 2.25 inches, and there are 4 smaller pips that bring the
gas from chamber labeled 3-4 to chamber 1-2.  The volume of these pipes
combined is 75% of the exhaust port size.  There are 8 holes drilled in the
plate that separates chambers 1-2 and 2-3 that lets the gas flow from 
chamber 1-2 to 2-3.  The total volume of these 8 holes is 75% the volume
of the 4 pipes.  The exhaust continues through the exit pipe from there.  The 
exit pipe is also 75% of the preceding eight holes. 

I soldered the 4 pipes into the holes drilled in the two inner plates.  The
Sears solder[I think melted at 1070 F, which, I thought was too high.  When 
the solder was hot enough to flow, so were my inner plates!!! Or it was VERY 
close to the same melting temperature.  I melted the first set of inner end 
plates, and had to turn two others!  I'd seriously look for some other solder
that melts around 500-700 dF!  Although, the article that you gave me does 
outlines some cautions of using the lower temperature solder.  ie Your second
joint will discombobulate yer' first! and so on...

The entire inner assemble fits into the 2.25 pipe snugly and is NOT soldered 
in.  I'm using two alan screws to secure the end caps, and this also permits 
me to slide the inner assembly back and forth by tightening one screw and 
loosening the other, in order to experiment with the sizes of the two end 
chambers, total volume remaining constant.

I used the mig welder to weld the intake and exhaust tubs in place. (I felt 
they needed more strength) I was able to use the exhaust manifold(round) that
came with my supper tiger and fit it to the 2.25 inch pipe prior to welding.

Well, this is my concoction... by no means is the best, or even right.  I'm 
just looking for a "quite" muffler, and I based my design on other mufflers 
that achieved such results.  I'm anxious to try it out once I finish the 
plane!  I'll let you know how it works.

Regards,

Brian

Oh, I used a Bernz-o-matic torch on the aluminum soldering to see
if it would work.  It was with this torch that melted my inner plates! 
So it does provide ample heat!  Use the small, concentrating tip.

Good job.  Looks like you tried to tackle something complex on
your first try, and succeeded.  Glad to know that the regular
torch with the pencil flame did the job.  I think that the solder
you used was at the melting temp of the aluminum.

How does the muffler mount to the engine; does it stick straight
out like a conventional muffler, mount to the back of the engine
with a curved pipe, or does it stick straight down? 

Oh, I forgot throw in those other tid bits!  The engine is a Super Tiger
bull ring 90.  It's going in my Balsa USA Citabria, and will be mounted 
horizontally.  So the way I drew the diagram is reversed(if you're facing 
the front of the plane) and the exhaust will exit through bottom of the 
cowl.  The new SS come with a two piece muffler that swivel 90 degrees.  
I used the header they provided, and used the MIG welder to fasten it right 
to the 2.25 inch pipe.  Seems quite rigged.

Yes, the solder I used was pretty darn close to the melting temperature of the 
aluminum alloy that I used... I'm sure they vary somewhat, though.  If
I'm not mistaking, the article you sent me said that K & B made some solder
that melted at 500.  I think next time I'll use it!

Keep me informed of your progress.

/Brian

                                                 
    How _quiet_ is it????  And do you still have good engine power?
    
    You may find your .75 ^ 3 restrictions a bit TOO restrictive for
    free exhaust flow; but that's easy to fix with a drill.  By my
    watch/calculator that means the final exhaust area is only .42 the
    cylinder-manifold area.  Only way to tell for sure is to try it,
    though.
    
    You say the spool assembly fits "snugly" in the tube.  How "snug"
    is "snug"?  You might want to put a few turns (as many as needed/will
    fit) of plumber's teflon tape around the spool rims to make a good
    seal of spool to tube. The red "flavor" of silicone rubber also
    goes up to 450F, it might be worth a try too.
                                                 
    I like the idea of having the internal geometry variable.  Nice
    touch!

    Snug is snug is snug!  I miced the inside of the tub prior to turning
    the round disks, and turned the disks to the same measurement. 
    One must "tap" the center assembly in, so I "think" that's snug
    enough.  What would you think??? Frankly, I don't think I could get
    any teflon tape in there, but perhaps some silicon gasket goop
    might do the trick if needed.  I took all RPM and noise level reading with
    the old muffler, and I should be able to try the new muffler by
    next weekend to draw some comparisons.
    
    I'll let ya know!
    
    /Brian
    

    If it must be inserted with a mallet, that's fine!  Congratulations!
    
    I assume no light can be seen at any point between the spool and
    the casing? (i.e. your spools were not warped by the heat of
    soldering)? 
    
    Good luck; I hope it sounds smooth, quiet and powerful.
    
    	-Bill
    

    No light! The inner disks/spools are .25 in, and I can't detect
    any warpage resulting from the heat.  So I "think" everything will
    be alright.
    
    These were my measurements:
    
    Exit port		 =.3 sq in
    4 tubes at 9/32      =.247 sq in
    8 holes at 5/32	 =.157 sq in
    
    
    Does this spound right??

>			I took all RPM and noise level reading with
>   the old muffler, and I should be able to try the new muffler by
>   next weekend to draw some comparisons.
    
>   I'll let ya know!
>    
>   /Brian
    
Well, what were the results? I'm interested because a friend of mine has
also built a muffler. This one is held together mechanically which might
be a little easier to build. He took dB readings with the old muffler and
as soon as he fires it up and gets som readings I'll post them here.

Dan Eaton

 Well.... I finally found time to try it this past weekend and Dick Bartlett 
 came over with his sound meter and tach.  We first ran and tested the
 the engine WITHOUT the muffler ...this read 107 db, turning a 14/7 Groupner 
 prop at 10,100 RPM(the noise level was read at 3 yards, 90 degrees from the 
 crank shaft).  With the muffler, we read only 92 db, with the same prop 
 turning 10,000 RPM!  I was VERY pleased!  The majority of the noise with the 
 muffler was coming from the prop, and NOT the engine... and I only lost 100  
 RPM.  The engine REALLY purrs! Dick mentioned that the some of the stock
 K & B mufflers that are reasonably effective, take as much as 2000 RPM from
 the engines performance!!  And, Dick's design knocked 1200 RPM off his ST 60.
 
 Well, incidentally, the 495th club is running a muffler contest to encourage 
 fellow modelers to keep the noise level DOWN.  The performance is measured by 
 the change in noise with and without the muffler, divided by the change in 
 RPM.  ...the results will be announced in the meeting Tuesday evening.  Gee,  
 sure would be nice to get some compensation for all my time and effort! :^)

 Dan, mine is essentially bolted together by the two end bolts, and the only 
 piece that "had" to be welded was the exhaust flange. 

 Oh,  The stock muffler's readings were 102 db with 9,800 RPM, so I guess 
 I came out ahead.  I'm not exactly sure, but I think 15 db is about 
 ten times quieter??  And, the remaining noise, although it still doesn't 
 sound quite like a four stroke, is very pleasant, and a far fetch from the 
 crackily, raspy sound I had before.
 
 I'd really like to hear how your friend makes out Dan, and how 'bout yours,
 JT?????  isn't your garage warm yet? :^).

 /Brian 

    Every 3 dB is a doubling (or halving) of the percieved loudness
    level.  So, you went from a stock 102 dB to 92 dB- that's like
    better than 2 x 2 x 2 or EIGHT TIMES quieter!  Very impressive!
    You are to be congratulated!  You might want to write it up as a
    mini-article for RCM.  Nahh, that would shame the manufacturers
    too much.                                     
    		:-)
    
    If you really get into muffler-making, you can do some funny tricks
    with pressure reflections and actually achieve a power INcrease
    (the so-called tuned-pipe effect).  It works by properly timing
    first a negative pressure (which actually sucks excessive fuel-air
    mix through the cylinder and into the exhaust manifold).  Then,
    after the piston has come up enough to close the intake port, the
    reflected wave makes it back and shoves the FA mix in the exhaust
    manifold back INTO the cylinder.  Before the pressure dies, the
    piston closes the port and you have more than .9 cu in. of FA mix
    in a .9 cu in. cylinder.
    
    It's like supercharging an engine - through the exhaust.
    	
    Unfortunately, it must be tuned to the top RPM of the final product-
    so you must sit there and iterate to get it right.... probably not
    worth the effort except for a hyperdedicated pylon racer.
                   
    Anyway, congratulations.  Fly it with pride!
    
    	-Bill
    

    It was a Winner... it took first place of $50!

    
    I noticed that Sheldon's hobby has a "new" muffler add-on that lowers
    the noise by 7-10 db's with increasing the power(in some cases)
    by 600 rpm.   Has anyone used this set up?? They tell us it sounds
    like a "four-stroke"???  can't remember the details or the cost
    off hand, but I think it's under 20$
    
    

    I recently read an article in the latest AMA magazine that talked about
    making home-made mods to stock mufflers to further reduce noise. 
    Looked fairly simple, so I went at it an worked up a simple device to
    go inside the OS .40 standard muffler.  It consists of two concentric
    tubes with holes drilled in each so that exhaust flows in a much longer
    path, first into the outer tube, then down the tubular space to holes
    in the inner tube, where they then pass into the exhaust port. 
    Yesterday, I tried it out, but no luck.  The engine coughed and
    sputtered, and never could reach any RPM above high idle.
    
    Does anyone else have any experience building this type of concentric
    tube muffler insert, and if so how do you get them to work?
    
    I suspect that the problem I ran into is too much constriction of the
    exhaust gases which in turn creates a back pressure into the engine. 
    Maybe drilling more and/or larger holes will make it work better.
    
    My stock OS .40 w/muffler measured 95 db at 9 feet at full throttle, so
    it seems to be a bit louder than it should be.  One thing I did notice
    about my home-made mod was that it made the idle much quieter, but I
    didn't think to make any sound measurements at that point.
    
    I'd be curious about what others have tried.
    
    Thanks,
    Joe

That was in the Gopher Canyon article...Joe, I looked that
article over for a half hour I bet and I couldn't figure out what
they were doing.  They gave beaucoup de data on performance and
photos and all...just didn't say anything about how to build the
darn thing!  A cutaway drawing would've been nice, don't you
think?

I can tell that dude ain't a technical writer!

    Has anyone tried to make an "inline" muffler for a 4 stroke?  
    
    The Junkers that I am building would look really neat if it
    had 6 exhaust ports puffing out the smoke.  I will have an
    Enya 1.20 on it. 
    
    I have read through these about welding and such.  Since it is a 4C, I
    suspect that a single chamber will be sufficient.  I have been thinking
    of using a piece of copper pipe with end caps and 6 pieces of brass 
    tubing directing the exhaust..
    
    Comments/suggestions?
    jeff
    

    Jeff,
    
    I doubt that brass and copper tubing will work for you on the 4-cycle.
    
    We have made similar mufflers for 4-cycle 1.20's without much success. 
    We used silver solder and the exhaust temp melts the joint in just a
    few secconds.
    
    I think you will have to a ferrous metal and at minimum "braze" it.  If
    you are someone you know is VERY good with aluminum you could save a
    little weight.
    
    Good luck,
    
    Chris
    

If you're coming down to the WRAMs show, I'm sure Davis Desiel wound have MORE
than enough opinions on it.

    No, I can't make it to the WRAM show, I have to go swimming, er
    skiing instead..
    
    I do have a friend that does a lot of welding..  I have also asked Dan
    Weier to pick me up one of those small butane tourches at the WRAM
    show.
    
    I should probably spend my time building my Nieuport anyways!
    
    Thanks,
    jeff
    

Davis Diesels has opinions???  Sheesse I hadn't noticed.

I had the rare opportunity to talk to this man at the show in Mass two years 
ago, and he is a marvel of self-promotion, part snake oil salesman, part 
preacher, and self-pronounced expert on everything. I find him to be 
dangerous in the "technical" explanations he gives.  For example, I told him 
I had used a piece of silicone tubing from my 1.20 four stroke header to the 
muffler, and that the tubing started to melt and decompose.  His response: 
impossible, because silicone is made from sand!!??  OK.

Next, he tells me aluminum mufflers won't work on four strokes cause the temp 
is so high it will decompose after a while.  I believe him and purchase one 
of his stainless steel mufflers for $55.  When I get it home and take a close 
look at it in my shop, I find one of the endplates is, you guessed it, made 
of aluminum. 

Although some of the products he sells are very good, I can't bring myself to 
believe he personally had anything to do with their creation.  The man 
behaves in such an obnoxious manner, I can't see how he has any personal 
credibility.


-Joe

I knew I'd get someone going with that suggestion but I expected it to be
Steve Smith 8^) I was across the aisle from him at one Wilmington show... I
got a 2 day supply of opinions 8^)

They had an aluminum welding demo at the end of my row that seemed pretty
good. Probably would have been helpful to see/purchase.

On another note, Any dates for a spring Gremlin Fling at New Boston? I need
to get the calendar in order.

Jim (back from a GOOD WRAM show)

Jim, no, I don't have any plans for a spring Grelmil contest.  I'll still 
hold one in October.

Regards,
Joe

Ok. Thanks for the info. I don't seem to be able to send you mail lately.
I've tried several ways and it eventually bounces. Let me know when you set
the Halloween date on the club calendar and I'll put it down on mine too.