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Marv -
Here is something else that I should have written to the LML a long time
ago...
Three and one-half years ago, after transporting my LNC2 back from
painting, I noticed a distinct squeaking noise whenever the plane was rocked
from side-to-side. It was coming from one of the main gear wells. Further
snooping led me to the conclusion that the squeaking was due to a shearing
movement between the main gear secondary attach point and the bottom spar
cap. This, of course, implied that the Hysol bond had broken. However, the
separation was not visible. The squeaking noise was the only indication.
At the time, I blamed it on a poor "fastbuild" bond, although I now
believe it could happen no matter how good a bond. While a severe side load
during landing places a tremendous stress on the secondary attach point,
another severe stress mode is simply rocking the plane from side-to-side and
bond failure could just as well occur then. I saw that a permanent solution
was to replace the design attach block (which bonded only to the lower spar
cap) with an attachment that spanned the full width of the spar cap
(contrary to first impression, a full width attachment would not interfere
with access to any other installations in that area of the gear well). If
the secondary attach point bond fails, then the primary attach plate must
resist the entire torsional load and might also fail, obviously resulting in
nasty consequences.
I called this in to Lancair at the time, but it went unheeded. Shortly
afterward, a Dutch builder/pilot reported almost all of the ten Lancairs in
Holland had discovered the condition and recommended the same solution. I
wrote this in to Lance almost two years ago, but it took what must have been
a rash of failures to prompt the subject SB.
The SB requires fitting and installation of a phenolic "brace" between
the top of the existing secondary attach block and the spar cap. This avoids
having to remove the existing block in order to replace it with a single
full-span attachment, which would really be the superior solution. I'm going
to replace the existing attach blocks with a single 1" x 2" square phenolic
piece, spanning the full width of the spar. I have a sheet of 1/2" phenolic
and will fabricate the attachment by bonding two pieces together, then
custom fitting it across the spar cap, leaving 1/32" top and bottom for the
Hysol/flox bonding mixture. I recommend this for anyone in the building
process who still has good access to the gear well.
Bill Rumburg
N403WR (Sonic bOOm)
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
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