Nose Strut O-Ring Was Bad...

On Feb 8, 8:32 am, "Jay Honeck" wrote:
Last week, in -22 temperatures, our nose gear drooped all the way to
the stop. Later, we were able to put some down pressure on the
stabilator (in the hangar) and bring it back up a couple of inches,
but made plans to have our A&P look at it.

Yesterday, since he wasn't coming in the shop till afternoon, we
decided to go flying first. My landing in Oskaloosa, IA (KOOA) was
gingerly -- a text book soft field landing, with the nose gear staying
high in the air till almost stopped. The strut stayed up around three
inches all the way to parking. The temperature was about 5 above
zero, and I thought that perhaps this had been a transient problem
that had "fixed itself". (We always hope, no? :-)

Not. Mary's landing back in Iowa City was fine, but the strut again
collapsed to the stop -- so we taxied straight to the shop. My A&P
told me that he could "service" it (basically, add air), but after
some discussion we decided to replace the seals in the strut. He
said that the O-rings were likely old (we hadn't replaced them in the
5 years we've owned Atlas), stiff, and perhaps "rolled", so that even
though lubricating the strut and adding air might do the trick for a
while, it would be a stop-gap measure, at best.

I helped him do it, and it took about an hour. (Of course, he's done
it a million times -- the job would have taken me all day, with
instructions, and I might have killed myself doing it.) But now, the
strut is sitting tall again, with new fluids, O-rings, and air
pressure.

Total: $65. Not bad at all, in aviation terms...

He says that it's SOP to apply brake fluid to the struts of the DC-9s
he services (at his day job) every, single time they park. It's
messy, as a result, but their strut seals rarely need to be replaced.

Problem there is the attraction of dust, which then fouls the
scraper ring and eventually gets under the O-ring and abrades it. We
keep ours just wiped off.
The cold weather makes the O-rings shrink and grab the strut
barrel, and then they roll in the groove and because their flexibility
is gone in the cold, they suffer spiral fractures. It's good practice
to replace them regularly. Granville Strut Seal added to the fluid
will sometimes help by swelling the ring slightly and making it a bit
softer.
There are far better O-rings out there now. I wish someone
like McFarlane would come up with an STC'd oleo kit that used
fluorosilicone or EPDM or some other advanced compound rings. Tougher
and with a better temperature range. There are "quad" O-rings
available, too, that would do a better job. In cross-section they look
like a four-leaf clover, so there's more contact area on two places
and they are more flexible, too. Double the sealing capacity, and
resistant to rolling.

Dan