Far be it for me, a humble late-builder, to chime in on this very
technical discussion thread; nonetheless, in the spirit of "open source
communication" with its underlying premise that an optimal solution to
the problem will arise out of the clamor, I have a few thoughts to
share. If I seem long-winded, my apologies, but clarity is my goal, as
I've had difficulty understanding some of the posts of others whose
brevity obscured (at least to me) some aspects of their intent.
As I look at my "pre-glassed" tailplanes which came w/ my "accelerated"
kit, the first thing I notice is that the pip pin recesses as supplied
bear no resemblance to the drawings in the manual...at the skin
surface, the recesses are round...about 1.25" diameter...and taper down
to a .50" hemisphere in which is centered the hole for the pip pin. So
I really have no assurance as to what extent the TP6 is properly bonded
in or exactly what is going on...I ponder this while reading about
variations (such as TP6 location) which others are discovering.
As I review Mod 73 and digest the insightful posts regarding the
process of accomplishing it, I can't escape my sense that...while it's
doable and apparently (at least to those with both the hands-on
building skills and technical knowledge to make such an assessment)
solves the problem...the mod seems like a bit of a band aid solution.
If I understand it correctly, it relies upon a proper bond between a
small crescent of a portion of TP6 to some bid cloth which transfers
any loads to the skin of the tailplane....I question whether I want to
rely on that bond to resist impacts from normal (and sometimes not so
normal) rigging.
If the fundamental goal is to simply keep the TP12 pins fully engaged,
I'm looking elsewhere from the pip pins.
I'm looking at the tailplane root close out which, on my tailplanes,
looks like about .088" of solid FG skin. I'm referring to the flanges
which measure a full inch in width...from edge to innermost surface of
the inboard plywood insert with the bushes which receive the TP12 pins.
I liked Carl P.'s suggestion (as I understood it) of a hardened steel
pin extending thru both top and bottom skins and lying inboard of the
TP12 driveplate. The FG flange could be suitably reinforced...perhaps
with an embedded plate which could be threaded to receive a threaded
rod, thus eliminating fasteners extending beyond the plane of the
tailplane surface. I did not understand Carl's calling for the rod to
be 9" long, as the depth of the tailplane at the root is just under 5",
but perhaps that was a typo. The beauty of Carl's suggestion is that it
is simple and direct...it is completely visable anytime the tailplane
is slid away from the fuselage an inch or so...and the condition of the
"fix" can be monitored at any time in the future.
Now that FG flange is only 1" wide, and the TP12 flanges measure 7/16",
and the bushes sit 1/16" proud of the glassed plywood...so...after a
(let's say) 1/4" dia. hole is drilled for a hardened steel pin to slide
past the TP12 drive plate, there's only a 1/4" left of the flange. It
would be sufficient however if the flange were reinforced with an
embedded plate which would allow the forces to be transferred to both
the top and bottom skins.
The steel pin could be cut flush top and bottom; perhaps only the
bottom plate would be threaded, and the top end of the pin could be
slotted for a screwdriver so the pin could be turned in place (and
perhaps loctite'd?). For redundancy, there could be two pins per side
as Carl P. suggested for the faint of heart.
With such a solution, the uncertainties of the conditions of the foam,
flox, TP5 placement, and other issues around the pip pins become
irrelevant.
Amen...thanks for wading through this post.
In the time it's taken me to write this, I may well have been able to
install Mod 73...and...there's always been more than one way to skin a
cat,
Fred
A194
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