-----
Original Message -----

From:
chris_zavatson [at] yahoo.com" href="mailto:chris_zavatson [at] yahoo.com" rel="noopener" target="_blank">Chris
Zavatson

To:
lml [at] lancaironline.net

Sent:
Wednesday, March 12, 2014 1:01 PM

Subject:
[LML] Re: Exhaust pipe failure

The 3/4 exhaust system is hugely cantilevered.  Long pipe
sections at the back end and each piece only has two bolts holding it to the
engine exhaust flange.  This is unfortunately a recipe for cracks - and
there have been many.  Since this entire exhaust layout is
rigid, it really needs a second support off the engine
itself.  Doing this will provide immense support and take
the load off of welds and the exhaust flanges.  

Cars provide a good example of exhaust design.  The
header and any rigid pipes are firmly bolted to the engine block.  A
flexible joint then transitions to the exhaust pipes that are hung off the
bottom of the car.  The engine is free to move without imparting stresses
to the header.  This arrangement is not foreign to aircraft, but the
360 exhaust was designed without a flexible joint.  If it had one,
the aft end could be supported
by a flexible connection to the fuselage or engine mount.  I
have seen a number of installations with a connection between the rigid pipes
and the fuselage or engine mount.  With this
arrangement, any engine movement will put a load on the
exhaust.  Effectively one has replaced loads generated by the
mass of cantilevered pipe subjected to vibration with loads generated by
the pipes being forced to move by the fuselage relative engine.  Which is
worse?  Many variables there.  I suggest avoiding
both sources of stress on the exhaust and either supporting
the pipes off the engine or adding a ball-joint.

On a related note.  One of my pre-flight items is to grab the
exhaust and give it a good pull in all directions.  Cracks take a while
to propagate around the circumference of the pipe.  As they do, the
stiffness of the system will drop substantially.  Any change in
resistance felt during this check is cause for further
investigation. 

Chris Zavatson

N91CZ

360std

http://www.n91cz.net/

       

On Wednesday, March 12, 2014 8:31
AM, Gary Edwards <gary21sn [at] hotmail.com> wrote:

That is the same joint I have had problems with in years
past.  On the second weld repair of it, I added a half round gusset
of exhaust tubing at the front side of the joint.  Haven't had any
issues since...at that location.

 

Gary

LNC2

-----
Original Message -----

From:
N4ZQ [at] VERIZON.NET (Greenbacks, UnLtd.)

To:
lml [at] lancaironline.net (Lancair Mailing List)

Sent:
Wednesday, March 12, 2014 5:43 AM

Subject:
[LML] Exhaust failure...

So much for our Bahamas adventure...
Yesterdays's flight
from KBVY to KOMN was uneventful until at 6k ft over STARY
Intersection,
#4 exhaust fractured completely, lots unusual noise, vibration and general
banging around in the engine compartment.
Brunswick Golden Isles BQK was
the nearest. So 4ZQ is broken for the moment but safely in a hangar there
and I'm driving to West Palm this morning with the broken exhaust
bits.
What I need at this point is a welder in the West Palm area who can
work his/her magic and try to make these whole again.
If anyone here can
offer a suggestion, please give me a call 978-994-4564.
Ideally, I want
to replace this exhaust but a weld fix should get me home in the
meantime.
The Lancair part # is EX-3/4-1 and according to Bill 5ZQ who
made the call for me, they don't have this and don't expect
to.

Angier Ames
N4ZQ

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