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.