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Guys,
As I read with great
interest last month the saga of possible improvements to the L360 scissor link
systems I deemed it appropriate to give a thorough inspection to mine on my
annual next month. Lo and Behold my annual came early.
Upon taxi out the
other day I was following my home owners association request to avoid the
new taxi way. We have several acres by which I can get to my runway.
It was crappy and rough for years so the HOA finally acknowledged who owned that
parcel and accepted responsibility to make it a functional taxi way. The
HOA started there project last fall by bringing in 5 yards of dirt and a half
hour of grading.
By"avoid" we mean to
taxi across the end of the new taxiway and stay off the remaining couple hundred
feet to let the grass grow. Long story short, it has been a dirt mud
pit since last fall. This spring an irrigation line was added.
Excitement was building. Rumor had it that seed would soon follow.
There still was no grass on the new dirt so we would taxi across the new taxiway
at the beginning and then down the hill to the runway.
All that is to say I
deliquately taxied across the dirt taxiway and stuck the right main in
the adjacent soft irrigation line trench. Moments later (or
less) the prop visited the earth.
What happened?
I figured the side loads on the nose strut caused my "weak" scissor to
fail. Indeed the scissor lower link was in 3 parts. But there were
more parts in spaghetti mode. Both hyd cylinders were askew and the
nitrogen strut had a 30 degree bend in the rod. The main T boss (part
number GM-?) was attached by only on end. You know the part, the chromoly
piece in the top of the wheel well with the 3/8" pivot rod going through the
nose tunnel?
The T Boss attach
point appears to be the primary initiator of the failure
sequence. Upon close inspection, the 3/8" pivot rod had been rotating
with the moving piece (read, lack of lube). The cotter key in cockpit was
found in pieces (under the EAR stick on insulation- who knows why I tolerated
that invisibility.... out of site out of mind..) Anyway, the rod appears to have
been easing it's way West for several gear cycles. The little bump into
the irrigation line trench appears to have been the last straw allowing the East
end of the rod to swing freely with the help of the nitrogen strut and bend the
3/8" pivot, unleashing all manor of devilish forces.
The fix....
May be nothing in your case. I believe larger cotter keys, inspection, and
annual lubrication would have eliminated the problem. I seem to
remember not knowing much about drilling stainless back in the day. My
cotter key was a wee little piece. However, there are at least two
additional things I am going to do to repair mine. First, I'll add a
grease zirt to the T Boss part so I can get lube to the 3/8" bushings.
Additionally, I'll use a roll pin on one end of the 3/8" pivot rod.
In conjunction with the roll pin will be a slotted mating piece of
phenolic. This will eliminate any possibility of the axle ever
turning.
That's what I'm
looking at so far. I'd like to hear any other
suggestions.
BTW, the scissor
link ("weak part") had very pretty holes after 700 hours and probably as many
landings. So far, I'm inclined to install new Lancair scissors and inspect
annually. Of course my good neighbor and fellow race junky Dick Keyt is
recommending Titanium.
The key to that
whole hydraulic over center link conversation (including the
mains) requires zero hydraulic over center
force. I assume that's a dead horse on the
list?
Larry
Henney
N360LH 700
hours
PS: Did I
mention the prop hit the ground... Da*&%$#!
PSS: Oh yeah, the
taxiway? 60 Workers daily all week. It is now a sodded, rolled,
pressed, groomed, fertilized, irrigated, putting green. They must've
thought their irrigation trench had something to do with my nose gear
collapse.
Remember, it is
preferable to collapse one's nose gear while taxiing as opposed
to flight.
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