Originally Posted by Owain Glyndwr
I really don't see the problem here.
Ny is computed from an accelerometer mounted near the top of the rear bulkhead.
If it is to be used to estimate sideslip then the reading needs to be corrected for rudder sideforce (deflection) roll and yaw rates. If airspeed information goes south then so does the estimated sideslip.
So far as I can see, the only use of Ny and/or sideslip in the EFCS is a part of the lateral turbulence alleviation function.
In Alt2 there is no bank protection (and therefore no spiral stability term). Consequently the EFCS neither needs nor uses either Ny or estimated sideslip for roll control in this mode.
In Alt2 the rudder deflection is controlled by pedal angle and yaw damper commands. The yaw damper uses yaw rate; there is no Ny or sideslip term.
Consequently the EFCS doesn't use Ny at all when Alt2 is engaged.
The estimated sideslip is sent to the PFD.
In the old days before automation, we pilots were confronted with a bunch of steam gages, one of which was the old needle-ball indicator. Ny is the analog of the old ball indicator. The rule was "step on the ball" to center it. All the jets I flew including a straight wing one had a yaw damper controlled by a yaw rate gyro. If Ny is used in the EFCS, it is not for yaw damping, but for biasing out lateral g through rudder deflection.
You seem to be in the possession of inside information regarding the arrangement of the 'bus control system, however how certain are we that the bus EFCS in Alt2 does not have authority to "center the ball" in Alt2, and only sends a signal to the PFD equivalent of the ball telling the crew to center the ball.
This seems to conflict with:
Originally Posted by A33Zab
The estimated sideslip (elaborated in FCPC) is NOT used in ALT2(& DIRECT) and replaced by Ny rear accelerometer.