Mailing List lml@lancaironline.net Message #70513
From: Chris Zavatson <chris_zavatson@yahoo.com>
Sender: <marv@lancaironline.net>
Subject: Fw: [LML] Re: Exhaust pipe failure
Date: Tue, 07 Oct 2014 08:55:40 -0400
To: <lml@lancaironline.net>
Tim,
This might be it.
Chris


On Wednesday, March 12, 2014 11:16 AM, Chris Zavatson <chris_zavatson@yahoo.com> wrote:


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
       


On Wednesday, March 12, 2014 8:31 AM, Gary Edwards <gary21sn@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 -----
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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