Al,

I have incorporated that slip fit myself in the design Bill Jepson and myself have been working on - but my welder is terribly slow.

Our design has duel cool air tubes, the outer acts as heat shield as well.

 

This is it awaiting the outer shield to be rolled and welded.

 

The small tube you see is cool air which helps to purge (and cool) the exhaust from the muffler.

The outer shield will be similar to what has been suggested on here.

Can't tell you what's inside, only to say it diverts the shock wave.

George ( down under)

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

From: al p wick

To: Rotary motors in aircraft

Sent: Thursday, July 27, 2006 7:56 AM

Subject: [FlyRotary] Re: Inconel

I have a lot of experience with failure analysis. Used to do it with GM, Ford, other warranty returns. One of my favorite experiences was solving a million $ warranty issue on a tubing product. Although I'm not expert in this area, I'd sure encourage considering other factors, other solutions.

In particular I'd encourage use of strobe lamp. Take cowl off, fire up engine, use strobe. (yes, it's dangerous with prop on) You will suddenly have appreciation for the forces involved. You should be able to predict failure points with this test. Tack together the broken one to see what I mean.

The exhaust will turn into a sine shape at certain rpm. You will see huge amount of movement on the busted one. Make a new design, compare movement to predict how long it will last. A very minor design change can greatly improve how much movement occurs.

I'm not sure this is applicable to you guys, but my exhaust design has slip fit of two pipes instead of welding. It works phenomenal. I've had conversation with other guys who welded instead and had failures. Same exact application. So my exhaust floats in relation to the header. I just attach a small bracket to the floating portion to prevent if from blowing off. Truthfully, I never expected it to work, but it has quite well. I might have pic if verbal description not adequate.

 

-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html

 

On Wed, 26 Jul 2006 14:22:34 -0700 "Al Gietzen" <ALVentures@cox.net> writes:

I say it is brittle because it has failed twice and both times quite spectacularly. Not only did the inconel fail in the area adjacent to the welds but spider cracks formed flowing out of the main cracks and into the surrounding area. It looked like glass might look if you punch a hole in it (i.e. not tempered glass!).

 

That is interesting.  Sounds like ‘stress corrosion’ cracking; which is the reason to use inconel vs other SS alloys at these temps.  Almost makes me wonder whether the welder picked up the wrong material when he made the parts; or at least didn’t give it any annealing heat treatment after welding.

 

http://www.corrosion-doctors.org/Forms/scc.htm

 

Al

 

 

 

-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html