Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Fri, 16 Aug 2002 10:07:24 -0400
Message-ID: <redirect-1689203@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: aluminum fittings
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<<Your point about fitting materials is a very valid one.  The fact that the
drains are aluminum is not. No pressure. The lines to your filter or cooler
are using pressure but it a continual pressure not a varying pressure line a
prop line. I would imagine that under the right conditions, a harmonic or an
"oil hammer" might be induced in the prop line which might be the reason for
Lycoming to go with steel fittings.

That's my SWAG!

Cy Galley, TC - Chair, Emergency Aircraft Repair, Oshkosh>>

If you can do it, I can take a swag, too.  The problem with aluminum
fittings in the engine compartment is mechanical vibration-induced fatigue,
not temperature or pressure-induced fatigue.  The internal pressure causes
stresses so low that it really has no effect.  The threads on a fitting are
perfect stress risers and aluminum has a very low fatigue limit.  Larger
fittings are probably stronger compared to the weight of the hose they
support so are probably less of a concern.  The temperature of the turbo
center section isn't hot enough to cause strength issues because its oil
cooled.  If it got hot enough to melt an aluminum fitting the oil would have
been long gone.  The failure in question was probably caused by vibration
and the ensuing fire melted the fitting, not the other way around.  I make a
hobby of looking at hose routings and fittings on kit planes (and certified
ones, too) and I see lots of questionable practices, mostly not allowing
enough bend in the flexible line to absorb the movement.  I plan to use
steel fittings firewall forward.  I like the idea of using steel fuel lines
in the passenger compartment, but haven't decided yet.

Gary Casey
ES kit, no fittings yet