Originally Posted by
wrench1
Curious. What are you defining "static droop" as? In the big picture, "droop" compensation is a function of the airframe N2 control system. Internally (engine/FCU/GOV) the GOV's sole job is to "reschedule" the FCU to maintain N2 turbine speed. There are several "precursors" which must happen before the GOV detects and reacts to maintain that N2 speed. Since the system is mechanical there is a certain "dwell" period between these "precursors" which adds to the transient time period between the GOV's detection and reaction to the power changes. Plus add a second or two for the GOV reaction signal to make its way to the power output of the engine.
FYI: In a B206, the term "droop" relates more to the positive/negative shift in M/R RPM when power is pulled into a hover from 100% Nr at flat pitch. If the Nr does not recover to 100% in a hover then that "droop" is compensated by airframe rigging adjustments. This adjustment physically changes the throw and range of the GOV arm arc as it moves in relation to the collective. It does not reset anything internally in the GOV.
I'm using the term "static droop" in the sense used in "Helicopter Test and Evaluation" (Cooke & Fitzpatrick) They define it as ( NR_min_power - NR_max_power / NR_min_power ) x 100%. Typical values seems to be 2-4%. Static droop being required for stable (non-hunting) operation but at the expense of constant RPM over the load range.
I think I understand how the compensation works, as it just pre-loads the speeder spring enough to offset the inherent static droop (figure from manual). In addition to helping the steady state be closer to 100%, the compensation also lessens the transient droop by introducing fuel immediately on collective movement as opposed to waiting for the RPM drop to manifest in N2.
RVDT , in is first answer, asserted "Droop occurs because the spring tension is non-linear and when it is back "on speed" to equal the spring tension it will be in a different place to equal the spring tension = droop. Google "mechanical governor droop"
Maybe this is the whole story and the inherent droop is just determined by the speeder spring strength. (and non-linearity - fuzzy on this detail)
I may have become confused by looking at "Governing Fundamentals" (Woodward power) They show how static droop can be engineered with a "droop lever" which "weakens" the speeder spring tension when fuel is being added. I think I assumed that this extra mechanism was necessary to create droop and we don't see anything like it in the 206 governor. However, if the governor can exhibit static droop just by virtue of the spring characteristic, then the question is answered.
To be clear, my question is just one of curiosity not an operational question, I'm figuring out how to fly it ;-)
John
By the way, I'm sure my reply other reply to wrench1 will show up in several hours after "approval". I just have to say, this forum is extremely unfriendly to noobies. The long lags in post approval combined with the inability to include images. It's like 1980 all over again. Maybe that's how you want it ?!