Thanx for the responses everyone.

 

The solution we came up with yesterday was as follows: Since the original “figure 8” profile was made out of two 2 ½” tubes that we cut slots out of it seems the best way to get a web across the center is to take off one of the halves and replace it with a complete and uncut 2 ½ tube.  I had some tube left from the original construction and that’s what we did last night.  Now we need to find someone to weld it all up. All we (really not “we” but my friend) tack welded it in place. But he was having real trouble getting it to weld and not just burn through. So we need to find a good welder that can deal with finicky material. The original welder is a real pro – so we’re going to see if he has any availability.

 

BTW the end caps on the tangential can are .060 inconel.  Anyone have an opinion on whether those will survive. At the time I built the exhaust everyone I talked to seemed to think that .035 or higher would be good enough – that’s why I essentially doubled the thickness. 

 

I may also just put on a stock exhaust manifold. I’ve got one so the price is right! Since I took the opportunity to remove my second alternator while I was tearing out the exhaust system I’ve got enough weight savings that I can afford the heavier manifold. But of course that will mean a change to the cowling - ARRGGGHHH!  The poor cowling has been cut up and put back together so many times it looks like a patchwork quilt on the inside where there isn’t any paint!

 

 

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On Behalf Of Joe Hull
Sent: Monday, February 27, 2006 2:10 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Exhaust Blowout

I'm still struggling with tuning my rotary/microtech. I spent an hour or so running it yesterday and ended up a little closer on the tuning front but also ended up with a blown out exhaust/muffler. It's come apart at a bunch of places - not the welds but the Inconel itself next to the welds.

 

The exhaust pipe coming out of the "tangential tube" is/was in the profile of an "8" without the connection in the center. An engineer friend of mine who looked it over said it makes sense - after the fact - that the exhaust pulses were causing the tube to flex at the center joint.  It appears to have started at the outboard end and went all the way to the center tube and then, perhaps from vibration, cracked out the pipes except for about ½" from the center connection.

 

The main manifold - runners and the tangential tube - are all sound with no signs of stress.

So, be careful out there!

 

Pics attached.

 

Thanx,

Joe Hull

Cozy Mk-IV #991 (Done Building! In Phase1 Flight Test - 0 hrs flown)

Redmond (Seattle), Washington