----- 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