Originally Posted by
autojohn
What am I missing?
Sometimes it's better to look at things from the other end in the beginning. The FCU controls the engine fuel flow from start through about 97%-98% N2 (at least on a Bendix). At around 98% the GOV starts to modify the air signals within the FCU. Each FCU and GOV are bench set to specific performance standards with the GOVs having two standards whether it will be installed on a single engine or twin engine aircraft (206 vs BO105).
When the FCU and GOV are installed on a particular engine they are individually "matched" to that engine: FCU max fuel flow setting and idle setting plus ensure the airframe throttle control allows the FCU arm to contact the full open and cutoff stops. The GOV is set to allow a N2 beep range of 97% to 100% with a spread of 3% N2 plus verify the GOV arm does not hit full open stop with the collective at full up travel.
Now with the aircraft running at 100% N2 with flat pitch, when the collective is pulled into a stabilized hover the N2 will droop but should recover to 100% (in a perfect world) within the defined transient time frame (5 sec). If it does not, then an adjustment to the airframe mechanical droop compensation system is required. In general, the droop comp sys is used to match different airframes to different engines. The droop adj is made by changing the mechanical geometry of the airframe droop sys torque tubes, cables/control tubes, and GOV actuator arm positions to allow recovery to 100%.
Since we're dealing with non-linear adjust values sometimes it is not possible to set the droop comp system to exactly 100% recovery. So if necessary you would electrically beep the N2 to 100%. Then leave it alone. Do not chase your N2 after this point. This type of engine control system contains a lot of lead/lag/transient response values that are "features" of the system: fly-weights, control movements, gas coupling between the N1 and N2 turbines, etc.
If you find your N2 erratic or hunting consistently with or without power changes then there is a problem with one of the system components which your beep switch is not used to fix.
Now to answer your original question. How the above takes place is determined by the sequencing of Pg, Pc, Py, P this, P that signals, the control paddles/bellows, fly weights, etc, etc. However, if the internal wiz-bang ops is still important I'll try and post the authoritative source for these FCU/GOV straight from Allied Signal-Bendix. Good luck.