From the sound of it, many contributors to this forum are converging
on a hypothesis about the failure sequence along the following lines:
- Slop builds up between TP12 and TP4. Perhaps this starts as a
finite amount of freeplay from an imperfect build and then continues
to build up through the repeated little impacts of the stabs and mass
balance bouncing off each other during normal and abnormal use, eg
taxiing over rough ground, effects of being trailered etc)
- Eventually, the slop builds to the point the pip pins are sharing
some of the torsional loads via the TP6s. This puts increasing load
on the bonded joint between the TP6 and the stab until one day that
joint fails.
- The implication is that the aircraft was not built with the "belt
and braces" geometry in the pip pin recess (is this correct?), which
would mean that the failed TP6 bond would permit lateral movement of
the stab
- the stab would therefore disengage both TP12/13 drive flange and
also the trim tab T bar. The Trim tab T bar would at this point also
be free to disengage from the other stab as well
- The system is now hugely different from the design condition: 50%
mass imbalance between the remaining stab and the TP19, one
unrestrained stab (perhaps it came off all together ), the other stab
perhaps detached from its trim tab. Flutter starts
- The implication is that events moved very quickly - no time for any
kind of distress message. The suggestion is that the flutter built
quickly and put severe oscillating loads on the rear fuselage,
perhaps torsional, and/or bending loads, until the rear fuselage
fractured (is it correct that it detached completely?), at which
point all control was lost
- At some point in or following the above sequence it has been
implied (in PFA 247/FSB 007) that there was a failure of the rear
wing attachment pin. If so, it sounds like this was a consequence of
the above, not a contributory cause.
Does this reflect the consensus about what probably happened and why,
or does anyone have an alternative explanation?
Willie Harrison
On 24 Jun 2007, at 01:30, Jos Okhuijsen wrote:
>
> Don't know if it's important, and i can't really oversee the
> implications, if it's important let somebody please bring it to the
> attention of the accident ivestigators. I doubt if they do
> investigate these archives.
>
> In one of the threads about the tailplane drive the following
> message has been written:
> -----------------
> Posted: Sun Aug 27, 2006 8:04 am Post subject: Re: Mod. 62 -
> Replacement of tailplane torque tube drive
>
> The other way is to clean the drive sleeve and torque tube surfaces
> with
> acetone and a jet of compressed air, then use a wicking grade
> Loctite to
> bond them together after lining up the tailplane trailing edges. It
> must be
> about 800 to 900 hours since I did that to mine and they are still
> solid. I
> will, of course, have to deal with dismantling if I ever have to,
> but a heat
> source inside the torque tube should do the trick. I also had to
> provide
> some lubricating tubes to replace the oil into the torque tube
> bearings,
> because the acetone washes that out too.
> Regards,
> William
>
>
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