Most of which can be rigged out unless the PTG is a duffer.
You should actually see a slight increase in N2 from flat pitch to hover as normal.
This is "droop compensation". Without it the following applies -
Droop has many uses and applications in the control of engines.
Without some form of droop, engine-speed control would be unstable in most cases.
- Droop is defined as a decrease in speed setting at the load increases.
Droop is expressed as a percentage of the original speed setting from no load to full load.
The normal recommended percent of droop is 3% to 5%. A minimum of 2.5% is required to
maintain stability in a speed-droop governor.
If, instead of a decrease in speed setting an increase takes place, the governor is showing
negative droop. Negative droop will cause instability in a governor.
In a system without droop, a load increase will cause the engine to slow down. The governor will
respond by increasing the fuel until the engine has returned to the original speed.
Due to the combined properties of inertia and power lag, the engine speed will continue to increase
beyond the original speed setting, causing an overshoot in speed.
The governor again will respond to decrease speed to correct for the overshoot.
It will over-correct the speed in the other direction causing an undershoot.
This overcorrection of speed in both directions (instability) will amplify until the engine trips out on over-speed.
This instability problem can be eliminated with droop. As the load increases, the speed setting is decreased.
When the governor moves to correct for the speed decrease caused by the increased load,
it will be correcting to a lower speed setting. This lower speed setting prevents the speed from overshooting.
Clear now?
