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.