Paul-

                  You indicated in a prior email that I was going to
   need to get
             my VAM
                  muffler re welded at the flange connection due to the
        existing weld
                  being
                  on the wrong side (the outside vs. the inside).

                  Does this mean I need to get the outside welds
   removed, or
             simply add
                  inside welds?  If I'm removing the outside welds, then I
        likely
             have a
                  problem, since cutting them out will remove much
   needed length
             on the
                  exhaust tubes -- I dont have extra clearance on my mount
        tubes
             to allow
                  them to be shortened.  What about simply adding support
             brackets from
                  the slide throttle down to the VAM to dampen
   vibration loads?

                  mrs

                  Looks like you will have to replace the tubes as the heat
        affected
                  zone would still be there. Also brace it back  up to the
        engine to
                  take the cantilevered loads off the tubes.

                  While you are at it use two smaller tubes instead of
                  one large one to quiet it down.

                  --
                  Paul Lamar ...No rotor no motor.



             I'll need a 3D of what you're proposing with respect to  2
   smaller
             tubes.

             What's the reason for the redesign?   If it is cantilever
   loads
        causing
             cracking, why not simply provide strapping to brace it &
   be done
             with it?

             mrs

             Its some of both. The cracking is occurring just out side
             the weld so what is happening is the molecular structure of
             the metal is probably being modified in that area. Perhaps
   it is
             becoming more brittle. The strap is insurance. Bad things
             happen when these pipes crack due to the intake system
             being so close. You have five years invested and $30,000
             so better safe than sorry. We now have at least two failures
             of the same kind.

             OK on the 3D's I'll do it tonight.

             --
             Paul Lamar ...No rotor no motor.

        Barring other concerns/limitations, things should be designed with
        structural efficiency in mind.  Doing so allows the use of  the
   lightest
        material and yields the best strength to weight.  Cantilevering
   anything
        is generally not good for structural efficiency..  Bracing _is_
   good
        however.

        In the case of the exhaust system, the operating temperature is
   high
        enough that the material is weakened, and it's attached to a
   vibrating
        machine.  The physical characteristics of the system material
   has been
        changed locally by welding - more brittle than the base
   metal.  Triple
        challenge.  Plus, as Paul said, the consequences of a failure
   of the
        exhaust system can be catastrophic - dangerous.

        Supporting the muffler via straps/struts takes advantage of
   geometric
        structural efficiency and can, by an order of magnitude, make
   the system
        more rugged and trouble free...  Even the conventional naturally
        aspirated aircraft engines often (usually?) have struts/braces
        supporting the mufflers.

        I am still convinced that slip/ball joints and or flex sections are
        needed on a 2 into 1 (muffler) system.  If your system has two
   separate
        stacks which aren't rigidly tied to each other (or something
   else), you
        might get away with out it (for a while).

        The locations of the flexible sections should be considered
   carefully to
        allow for the pieces of the system to change
   dimensions.  Ideally, it
        seems that one of the pipes that leads from the engine to the
   muffler
        should have a flex coupling in two places plus a slip fitting,
   while you
        could probably get a way with the other pipe not having
   any..  Doing
        this would allow the muffler and the engine to change sizes pretty
        dramatically but not put any stress on any of the welds.


        Regards,

        Matt-

        Matt please take a look at this. I just updated it.
        http://www.rotaryeng.net/exhaust.html

        Paul Lamar

   The Hatch style system looks good to me..

   http://www.rotaryeng.net/everexh.jpg

   This one looks like it would run for a while, but eventually fail -
   short, rigid stacks I assume, but can't see from this picture.

   http://www.rotaryeng.net/Ed-Klepeis-p8050012.jpg


   Regards,

   Matt-


   Thanks Matt.

   Paul Lamar ...No rotor no motor.

   Here are the 3D's Mark.
   --
   Paul Lamar ...No rotor no motor.



Any particular reason the exhaust tubes are square stock vs round?

Mark Supinski

Supposedly that makes it quieter. You can try some inch
and half round instead. A bit cheaper to build.
You don't need to do this if you can live  with the noise.