You make some fair points, Carl. I think police detectives call it
the ABC approach: Accept nothing, Believe nobody, Check everything.
I can only agree that it is in our interests that the investigators
take as much time as is needed to get the right answer, even though
that leads to short term anxiety and frustration.
I'm not sure I agree with what you say about stick forces since you
are not just trying to counter the deadweight of the remaining stab
but the dynamic forces from the self excited oscillation which is
drawing enormous energy out out the airflow.
I could imagine either or both of the decoupled stabs fluttering. If
it is true that the tailplane fractured off the fuselage then it
suggests that structural oscillation in the fuselage may have been a
component of the flutter (?like the V-tailed Bonanzas??)
Willie Harrison
On 23 Jun 2007, at 15:01, Carl Pattinson wrote:
> <carl@flyers.freeserve.co.uk>
>
> It isnt a matter of keeping people in the dark but of arriving at
> the correct conclusion. IMHO it is far better to say nothing than
> to arrive at a flawed judgement.
>
> And as for this being a British phenomenon what sparked off Tony
> Blairs war on Iraq. The assumption that they had WMD with little or
> no evidence to back it up. OK, sorry for getting political.
>
> It is to be commended that the PFA have responded so quickly to
> this situation and I doubt very much if the answer is as clear cut
> as people may wish. At the moment their priority is to prevent a
> recurrence of this tragic accident even if it means barking up a
> few wrong trees. When they have had the opportunity to fully
> consider the evidence I am sure we will be amongst the first to hear.
>
> Purely on the speculation that one of the tailplanes may have moved
> outboard and disengaged the drive pins it is a possibility. However
> I think it highly unlikely that the disengaged tailplane could have
> "turned square" as has been suggested. If you consider the area of
> tailplane foreward of the torque tube as compared with the area
> behind, air pressure would keep the tailplane in line with the
> aircraft. I suspect that once disengaged from the drive pins the
> unrestrained tailplane would start to oscillate and then flutter.
>
> What effect this disengagement would have on the remaining
> tailplane is hard to predict. True there would now be an imbalance
> in the tailplane assembly but any force exerted by the mass balance
> arm could be counteracted by force applied to the control column.
> Have you never sat in the plane withouthe tailplanes connected and
> moved the stick back and forth. It is heavy but not impossible to
> move.
>
> As for it being unlikely that flutter would occur at 90kts my
> understanding is that flutter can happen at any speed. What speed
> does it take to cause flags to flutter in the wind 10-20knots (even
> less).
>
> I believe that if there had been a straightford and simple
> explanation, we would have heard by now. It is in nobodys
> interests to keep us in the dark.
>
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