In modern turbine helicopters there is a governor which keeps rotor rpm (NR) at 100% and for the most part it does a very good job at doing so. While there are situations which could cause NR to drop below 100%, under most normal circumstances it will be at and remain at 100%. Early turbines suffered from compressor stalls which could led to surging or flameout when rapid changes in fuel flow were made. Modern governors have the benefit of working more quickly and smoothly then a pilot ever could and hardly ever make a mistake. Most of the default aircraft don't maintain their NR very well however I was content to ignore this under the assumption BIS had bigger fish to fry until I saw SPOTREP #00076 and referenced T126770. Needless to say I was delighted as it appeared BIS was attempting to address the problem which has been bothering me for some time. Unfortunately after installing the update and doing some flight testing it appears the underlying issue still exists.
While N1, N2 and NR are now matched up better while at flight idle on the ground NR is still all over the place in flight as the rotor is loaded and unload and if you would like to fix it I would like to help. I believe the correction involves raising the parameter(s) that control rotor inertia slightly so the blades will hold more energy and will not tend to droop as readily. If anything they should have a tendency to overspeed which can be corrected by raising collective slightly. Now if there isn't a single value that handles the blade inertia it would be worth while experimenting with making the blades slightly longer or heavier or a combination of both to help increase the inertia hopefully without adversely affecting anything else.