Mailing List flyrotary@lancaironline.net Message #30438
From: Ed Anderson <eanderson@carolina.rr.com>
Subject: Re: [FlyRotary] Exhaust Blowout
Date: Mon, 27 Feb 2006 07:32:56 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Joe, I have found that the strong exhaust pulses (not the heat) are very detrimental to the life of Stainless Steel - especially if its a bit on the thin side.   The 200+ pulses per second appear to fatigue the metal very quickly.  I found that 0.048 thick SS tube would last approx 5 minutes at full throttle.  Heavier gauge metal and some inserts to break up the shock wave seemed to help.
 
Glad you caugth it on the ground (best place for any/every thing to go wrong that's going to).
 
Ed
----- Original Message -----
From: Joe Hull
Sent: Monday, February 27, 2006 2:09 AM
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 ˝” 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


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