.----- Original Message -----
From: "Carl Pattinson" <carl@flyers.freeserve.co.uk>
> Ivans idea behind the original tailplane attachment was to produce an easy
> and quick way of rigging the aircraft. Regrettably time has proved this
> design to be inadequate in terms of security.
Carl, I think it's not correct to say that time has found the design to be
inadequate. William's plane in one critically important respect was not
built to design. He did not have a standard pip pin recess, but instead a
hole rather like the undersurface drain hole, down which he fished with a
sort of crochet hook to get the pin out
William was intelligent, thoughtful and meticulous and also had
more aeronautical engineering experience than nearly all of us, but the
redesign of that area meant that he had no sensible way of checking the
security of TP6 bonding, and also that there was nothing but foam to stop
the tail plane migrating once a TP6 did disbond. Also he regularly
dismantled his plane, so possibly was at greater risk of the TP6 becoming
disbonded by repeated impact on the end of the torque tube.
Like many of those who have contributed I felt considerable unease
until I had an explanation for the known events: that is that the tail
elements broke up/off while he was in level flight at 1000 ft and 100 kts or
thereabouts, when it appears that there had been no problems with him having
previously done his renewal test flying including a Vne dive. Flutter
starting out of the blue a t such a speed made no sense when we know much of
the fleet has varying degrees of slop yet regularly survive Vne
dives.However the loosening of a TP6 with uncoupling of the tailplane drive
pins is an entirely plausible explanation for the events as so far known,
and makes me feel entirely comfortable with my plane again.
As far as the solution goes I also disagree that it is a mere
'sticking plaster'. If the pip pin recess is as designed we can readily
check the position and any movement of the TP6. To have shifted the tail
plane laterally in relation to the pinned TP6 would entail tearing the pip
pin through a visible fibreglass lay up and would have needed considerable
force. To pull a TP6 disbonded from the rib through the upper lay up and the
new underside lay up would, I strongly suspect, take several hundred pounds
force - yet there are no strong lateral forces naturally occurring on the
tail plane. On doing mod 73 I found my TP6 to be rock solid in the rib on
each side, as indeed David Corbett reported for the three he has done.
I for one will continue to enjoy flying my plane with the same
confidence it has always given me (which is more than the confidence I have
felt in various certified planes I have flown over the same period).
Regards, David Joyce, G-XSDJ
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