The only "solid" material on the inboard side is 2 plies of bid comprising
the pip pin recess (and a bit of foam!!!) . That is why the PFA have been so
specific as to what is considered acceptable or not.
The tailplane rib is on the outboard side of the pip pin recess and would
provide no suport to a disbonded TP6.
You say that the pip pin head is located against "solid material" but what
is that solid material anchored to? If it isnt anchored to the tailplane
surface or to the outboard tailplane rib then it isnt anchored to anything !
I suspect the current mod 73 will prove to be no more than a temporary
solution and a more robust mod will follow in due course.
There would seem to be several retrofit solutions to this problem and
ultimately it is up to the PFA to decide which will be best in the long
term.
Whilst I agree this problem should have been addressed a long time ago, the
fact is that many Europas have flown many hours without incident. This
would suggest the problem is not as dire as we all think it is. I suspect
that 99% of Europas are flying around with secure tailplanes but in the
absence of definitive proof one has to assume the worst.
We are also assuming that a disbonded TP5 contributed towards Williams
accident. So far however there is no definitive evidence to support such an
assumption (in the public domain at least).
Carl (with a C !)
G-LABS
----- Original Message -----
From: "Karl Heindl" <kheindl@msn.com>
Sent: Sunday, July 15, 2007 2:49 PM
Subject: RE: Europa-List: Europa Tailplane - Mod 73
>
>
> Nigel,
>
> I understand all that and your mod should have been made standard a long
> time ago. But what about older Europas ? We hear reports about disbonded
> TP6s but we don't hear how they were repaired. I really would like to
> know. A suitable retrofit mod should also have been made available as soon
> as this problem was known.
> I still say that there is no way the tailplane can move if the pip pin
> head is firmly against solid material on the inboard side. You say there
> is always a gap, but that gap is filled with floxed epoxy, and the head is
> inside a close fitting plastic pipe in my case. I think another builder
> recently told us about a similar mod he made. The remaining space around
> the pipe is also filled with epoxy. Of course all these solutions are
> based on theory and only a lab test could verify the claims.
> When my TP5s disbonded from trailering I was kicking myself for not having
> installed a one-piece pipe, but in those early days I was very careful to
> follow the build instructions precisely. I stll think that a retrofit of a
> one-piece sleeve would be more than strong enough to prevent any future
> disbonding, and would be a relatively easy solution where the TP6s have
> already disbonded.
>
> As far as the accident goes, we still don't have any real conclusive
> evidence about the sequence of events. Only a number of theories. Only a
> wind tunnel test would verify the flutter theory, but who is going to pay
> for that ? Eyewitness reports can be very misleading.
> If the wing trailing edge pin came off first, is it possible that the
> pilot was getting set up for landing and deploying flaps and undercarriage
> ?
>
> I also like the other suggested solutions where a lock is put behind the
> TP12
>
>
> Karl
>
>
>>
>>
>>
>>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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