Matthew, i have often wondered if the yaw stability system need be this elaborate. All you really need is something which keeps aircraft yaw rate directly proportional to pedal positions. I have considered this as part of my pet interest in simple mechanical SAS designed into control systems for light helicopters. The idea being that the system is simply a funtion of the control, in all flight conditions, rather than a failsafe add-on.
In the same way that using a gyro can force a cyclic to provide direct pitch/roll rate control, it could force pedals to provide direct yaw rate control. The complication comes from the need to ignore pitch and roll, so this implies two counterrotating gyros. These would be differentially actuated by pedal position above and below gimbles, with gyro axis either longitudinal or lateral. The tail rotor connects to gyro assy to keep the gyro assy in the same orientation inside the helicopter. Any external influence, means gyros don't move so heli gets pulled back. It would mean that Aser's pedalless days would be over, but pedal control would be linear in all flight conditions.
Apologies that this could do with a sketch, but hopefully you will see what i am getting at. The objective is a simple reliable system which gives 90% of what SAS would, but has no wires or electronics - ideal for light heli applications.
Mart