Dear All
Graham's findings and analysis have the ring of truth about them. If the
fits were good when new, then the problem would arise from inadequate
bearing strength on the walls of the holes into which the pins fit - it's a
common design problem. The situation could be improved by fitting multiple
pins or bolts or (better) steel pop rivets, but this would probably demand
re-certification of the design in that area.
Loctite make a couple of wicking adhesives which are thin enough to find
their way into the small gaps between the tail plane drive plates' sleeves
and the drive tube - 601 and 603 (the latter being oil resistant) This of
course would mean we'd say goodbye to ever parting the two on the aircraft,
since significant heat would be required to melt the adhesive, but was
this ever possible anyway? There is also the disadvantage that there is
poor control over the extent of the wicking along the tubes and we don't
know how dirty it is in there. You wouldn't need much to do the trick
though. To resist JAR VLA Pilot Forces, I calculate only a TOTAL of 20 mm
length; and this takes into account dynamic loading and a safety factor of
2. I reckon it's feasible to run 5 mm in to each of the four access
points.
Maybe just bore out the tubes' pip pin holes to 3/8". What the hell.
Dave Simpson
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> From: Gramin@aol.com
> Subject: TP6's and transferred strain.
> Date: 29 January 1999 00:07
>
> Re. the recent traffic on strengthening the TP6 bond, it seems possible
that
> we may have been trying to cure the result and not the cause. I have now
had
> to do them twice in spite of considerable roughening, inserted screws and
> dimpling. More than one of us has now found this to be associated with
> slightly slack drive plates (TP12). These are held to the tailplane tube
by
> pins. If there is any slackness at all here, then the load is
immediately
> taken by the pip-pins and through the TP6's into the bond which is not
> designed for such loads.
>
> I find that the rear of one tailplane can be lifted relative to the other
by
> 4mm and another builder is finding 10 mm ! Neither of us believe this to
have
> been present at build time. This points to development of a significant
> enlargement of the hole(s) carrying the pins which secure the TP12's.
> Effecting a cure here inside the fuselage is difficult. Either the
existing
> holes need re-boring and larger pins fitted, or extra pins/rivets are
needed
> to attach the TP12's.
> This is significantly major for us to await a factory response. In the
> meantime I would suggest everyone check for relative movement of the two
> TP12's on the tailplane tube. Both of these aircraft have done under 100
hrs.
>
> Graham C. G-EMIN
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