THS Rates & Trim terminology
A33Zab,
That explanation is invaluable, thanks. So it's only too easy to get confused between the electric (control) motors and the hydraulic (actuation) motors...
From the auto-trim point of view, the movement from 3NU to 13NU (after FL375) was very nearly continuous? I guess it only uses the one speed of 0.2deg/sec, as quoted by PJ2. Although you state a 2-motor speed of 0.4deg/sec, perhaps limiting the speed to 0.2 would avoid any slow-down if either the blue or yellow hydraulic motor failed?
On the face of it, those who have advocated use of manual trim-wheel in stall recovery seem to be vindicated, as its 1deg/sec might be needed. The argument probably only applies in Pitch-Alternate Law. We still have no idea what the effect of full down-elevator is when the THS is at 13NU. (That is: what would be the equivalent THS setting with neutral elevators?) Sadly, the answer does not seem to be pertinent to this accident.
Quote:
Since the hinges are on the trailing edge and therefore the aerodynamic load on the drive spindle is in the AND (stab. Nose Up) direction...
Please forgive me for offering readers a warning on terminology here, from my experience of various jet transports with THS under one name or another. "Nose-up" is a term normally used to indicate the trim-effect on the aircraft, not the physical position of the THS. Because the THS is hinged at its aft spar, it's easy to think of "nose-up" as meaning that the leading-edge of the THS is up. Not so.
For maximum nose-up trim, a THS is at its fullest NEGATIVE incidence, with its leading-edge fully down. The A330's mechanical limit seems to be -14 (see PJ2/mm43 discussion). We call that "14 degrees nose-up" (14NU). For a typical take-off, the THS setting calculated on the trim-sheet by load-control might be 3NU. This requires the incidence of the THS to be -3 deg. However, load control and most pilots refer to it as "+3". Confusing, perhaps, but that's the way it is.