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Message
please don't take this as
being critical, I'm just asking - is it true or not that engine fittings should
be steel, not aluminum? or is that just a myth? does aluminum fatigue
faster than steel? what do certified piston planes use?
Kevin Lane Portland, OR
This
is sort of a controversial subject. There is probably an official FAA
rule, or at least rule of thumb about only using steel fittings when
there's relative motion on the two ends of a hose. Of course
screwing steel fittings, into an aluminum gear drive would also violate
some dissimilar metal rules, so damned if you do, damned if you don't.
Since
I was schooled at the Van's Aircraft institute, I follow the more
common sense rules. If it's a small fitting, that isn't very strong, it's
best to use steel. If it's a fairly large fitting, then aluminum is
plenty strong. AN-6 is about the dividing line, and it comes down to
whether there's much motion. In the case of the drain fitting you see in
the pic, there's no relative motion, so I feel aluminum is
fine.
Cheers,
Rusty (not an
A&P, and don't even play one on
TV)
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