mm43
Hello again. I think a discussion of Tail strike protection would be fruitful. The first consideration is to spread focal stress as the tail hits and the VS wants to keep going. With a pitch sufficient to hit tail first ~17 degrees, the Hinge axis of the rudder is roughly 34 degrees off vertical and the arm restraint would be roughly 90 degrees to the deck, so the effort seems to point to protection of the Rudder from deforming the hinge plates from a linear alignment (all seven). If the hinges deform from line, the Rudder will Bind, and not perform, an expensive fix. In this way I think the arm makes sense. OldEngineer points out the increasing danger of arm failure as the attach point decreases in size, specifically Bolt Size. The other way to express this is to say that as the attach points increase, not in mass, but in bedded area, the forces are attenuated with less structure and less risk of breakage. In arm 36g, the bolt subtracts substantial cross section from the arm, such that a failure such as we see in 447 is not surprising. Without sounding arrogant, I think rather than an arm, with its attachment vulnerability to tension, perhaps another way to address the "drop" of the Rudder relative to the VS, to protect the Rudder hinges would be to fasten plates to the spar and the Rudder Pinion, such that rather than focal (tension) strength, the area is protected by a more familiar shear solution. This would be addressed by a composite of sufficient cross section to carry the load away from the hinges, and load the Aft Spar of the VS spanwise to the Rudder Pinion(s).
It may be that the arm is after all not intended to "Balance" the shear forces of the two control surfaces under landing and tail strike events, so I have to wonder what the purpose of featuring the picture of the arm is meant to convey. At first I assumed the Picture and the numbers were included for people to make of it what they may. BEA makes no actual finding re: this arm, so does anyone have a more evolved take on the Arm issue?
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Cheers, and may the recorders be found.
bear