From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of Ed Anderson
Sent: Thursday, July 27, 2006 5:34
AM
To: Rotary
motors in aircraft
Subject: ***SPAM*** [FlyRotary]
Re: Exhaust pipes
Just for another reference point, I have two 2" dia
0.11" thick stainless Steel (304) pipes as my headers. Each header
is approx 18" long and make one 90 deg turn before exiting out the bottom
of the cowl. I now have over 400 hours running time on these
headers. They were welded by an aerospace welder who used to weld
turbine blades - need I say a great job? Since the two pipes
are not attached to the same point anywhere, any heat related expansion
stress is at a minimum.
----- Original Message -----
Sent: Thursday, July 27,
2006 12:47 AM
Subject: [FlyRotary] Re:
Exhaust pipes
From the pictures of his exhaust system, it appears that the pipes were
supporting the muffler can. My understanding, is that the entire exhaust
will glow red, and the metal will soften (as in almost melt) at high power settings.
The melting point of inconel is over
2500F. Things will start to glow at about 1000F if the light isn’t
too bright. It is still quite strong at our exhaust temps. It is
worth noting that one of the features of expanding the gas into the large tube
is that the temperature drops (Charle’s Law of expanding gases); the temp
of the large tube is somewhat below the temp in the header (how much lower
depends on too many factors that I don’t know) and depends on
backpressure and engine rpm.
Al W. brings up a good point. I had been
primarily considering thermal stress, but stress due to vibration from the
engine (aside from exhaust pulses) could be a major factor. Some
high frequency resonance with engine vibration could do a job on the
welds where joe’s broke; or a resonance with the unsupported exit pipe?
I guess I’ll learn some more as I
accumulate some hours on my plane. Now a real challenge is coming up with
some kind of damping support . . . .
Al G.