<kheindl@msn.com>
Can anyone explain to me how the tailplane can possibly move outward by even
a millimeter when the pip pin head is resting firmly against a solid wall on
the inboard side..................................Snip
Karl,
I have attached below, an excerpt of a long mail I sent to the PFA that
describes a sequence of events that could lead to the tailplain moving
outboard. Out of interest, there is always a gap between the pip-pin and the
face of the rib.
This was sent before the current Mod 73 was issued, but you will see why the
temporary remedial action has been to reinforce the pip-pin hole.
Nigel
-------------------------------
Excerpt
...... The only thing preventing each tailplane moving sideways is a single
pip-pin that passes through the TP6 bush and into the TP4 torque tube. (See
Fig.5 Chap 4)
The design relies on a good bond to hold TP6 in place, however only the
protruding outer 12mm (just 8mm on TP5) is required to bond to the tailplane
rib that will subsequently be laid-up onto it. Epoxy adhesive does not bond
well to stainless steel - so the potential for this bondline to fail is
great.
This tiny bondline is the only "design" load path to prevent the tailplane
moving laterally. If the bond failed, the loose TP6 bush would tend to push
its way inboard into the soft blue foam, allowing the tailplane to move
outboard. The TP5 bush would offer no resistance since it would simply slide
along the TP4 torque tube.
In some early Europas, this TP6 bush has de-bonded and it is only the
laminations into the "PipPin" access hole that prevent any lateral movement
of the tail-plane. This lamination was never intended to be structural. If
the aircraft is high-time and habitually operated off rough strips, it is
logical to predict that the continual fretting would cause the glass around
the pip-pin hole to chafe, opening up the hole to a point where the whole
tailplane could slide far enough laterally to allow the tail-pane drive pins
(TP12) to disengage from their drive bushes (TP13) - The tailplane would
then oscillate violently with catastrophic results.
Modification 10672) calls for both the Stainless TP5 and TP6 bushes to be
laminated into an epoxy/Bi-Directional Glass tube before inserting this into
the tailplane TP2 cores and laminating the ribs. This bonds both bushes over
their entire surface area, significantly increasing the bond area and more
importantly, physically tying TP5 with TP6 and both the inner and outer ribs
together. With this structure, the entire bond surface area and both ribs
would have to fail before the tailplane could move sideways.
The loadpath is through the mod 10672 and not through the outer skin and
pip-pin hole - a significantly better engineering solution.
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