N2/Nr drop
Hi,
Here is a control systems answer, not a S76 experienced technicians answer.
Control systems can be made as complex as imaginable, but in practise they tend to be based on simplified rules.
The static droop referred to is associated with a static feedback system (proportional control). If the control is calibrated for two engine operation, then the loss of an engine will create an N2/NR offset that makes the proportional control react (proportional increase in fuel flow). There is however always a 'remaining offset' necessary to drive the control system when operating out of its design point. So a disturbed proportional control system will always display a static offset.
Now most systems are not just 'proportional systems', and classical control theory would among others include 'integral control'. The latter 'integrates' or 'sums over time' the control error to drive the correction, so over time it will reduce the control error to zero, since as long as it sees an error this error will drive corrective actions. This is equivalent to thinking that this system is capable of compensating the permanent offset. The problem here of course is that some care with this permanent driving should be exercised not to create dynamically unstable or out off limit situations.
So to me it seems that the system is close to a (basic) proportional control system.
d3