----- Original Message -----
Sent: Monday, August 23, 2004 9:31
PM
Subject: [FlyRotary] Re: Sorry Rusty - no
bind
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)
This topic was
recently discussed on the canard aviator's website....seems that Lycoming is
sending their brand new engines with aluminum fittings. I agree, however
that there is comfort in using steel for the smaller (-4) sizes. I have
-16 aluminum AN fittings for my radiator hoses, and it would take a
sledgehammer to damage one of those aluminum fittings. The general consensus
on the canard site was similar....steel for the smaller fittings, but aluminum
was fine for -6 sizes and larger. I guess they figure that if Lycoming
can supply a certified engine with aluminum fittings, it's OK on our
experimentals. FWIW. Paul
Conner