droops...
Transient droop is the reduction in rotor speed following a sudden change in power demand (increase), for instance recovery from an autorotation will produce for a short (transient) time an underswing in rotor speed below the nominal governed value before the engine governing system reacts and recovers the Nr to nominal.
Static droop is a function of a non isochronously governed rotor system where the nominal rotor speed reduces as collective pitch increases. The Lynx for example, when fitted with the Gem exhibits a 'droop line' characteristic with a lower Nr at higher collective, this seemed to be a fucntion of the control system technology available for that generation of engine. FADECS have eliminated static droop in most cases.
The other type of static droop is where the power demand exceeds the power available (such as when an engine limit is reached) in a steady state case and the rotor doops for that fixed collective setting. This may be caused by either engine or transmission limiters working. In some cases this limit may be 'soft' and when a certain % of droop is experienced (for instance when you REALLY need the power) the limiters disappear and rotor speed will recover
hope that helps
DM