Diversification
Yes, the Arm failed while in tension, ostensibly "picking up" Stress produced in the Rudder's "Down Axis". Yes, again, for the Rudder to have endured its damage from the tail cone, the vector would have been opposite, in the "up" vector, as the Rudder was pinned to the upper Fuselage and the VS kept going. This holds true with the Rudder in a variety of deflection angles. So the "prying off" theory needs another look.
It may have been weakened by corrosion, these Hinges are open to the Air. Also, the Bolt seems to have remained in its position, meaning that there was little tension damage (if any) to the remaining Arm. Also notice that the Pivots of the Hinge, the two plates bracketing the joint from the Aft Spar of the VS, seem unscathed. There is no deflection or cracking of these plates nor the pin carriage on the Rudder. The Hinges must remain oriented in a straight line, if there is deviation from straight, the Hinge can "Bind" and cause problems with the actuator.
Something does not square in the description of Rudder Hinge failure. If the Vertical Arm breaks before the Hinge does, it is apparently not intended to prevent catastrophic failure and Rudder separation, and if the Rudder Hinge is not damaged, why then is this Arm present? Alas, the Arm failure occurred at the place of minimum material, so by interpretation, the length of the Arm that is composed of additional Metal is overengineered. One wonders why the Bolt/Arm mate is not built with additional structure, eg, an "Eye" (a circular pan with its hole in center of sufficient diameter to preclude a failure here; the Hinge end of the Arm is tapered, and I assume the "Barrel face" is radiused to conform to the circumference of it's round bed).
The simple way to see this is to say that in spite of the horrific load the VS and Rudder endured, it was the VS that failed, and separated from the a/c, not the Rudder. Also if there was sufficient energy to shear the VS, that same energy failed to separate the two surfaces. As you say, the bit of Arm that snapped off looks like a corrosion crack/fail.
The engineering consideration of the VS join is lateral energy, obviously for the ability to handle very serious loads imparted by the Rudder. The collateral consideration is simply to remain with the Airframe. BEA'S theory of vertical failure happens to pinpoint a stress for which the assembly is built exceptionally strong, but not as a result of consideration of failure in this direction. It is a bonus that derives from the VS' layout atop the Fuselage. Given that there was upset, loss of control, and impact in the Water, I simply maintain that it is strange, no, highly strange that the vertical Stabiliser was torn out virtually "over itself" and in a mode that is resisted in the VS structure here, with the presenting energy defying great odds. Possible.
bear
Last edited by bearfoil; 9th Mar 2010 at 01:21.