Has anyone here logged steady-state data on modest RPM droop in cruise? On a 4-blade head with −10° linear twist, dropping from 408 to 370 rpm at 110 KTAS cut required power about 3% (ISA+15 at 5,000 ft), but the inflow distribution shift and 3/rev moved enough to be noticeable — where does your sweet spot land, and how are you safeguarding retreating-side stall margin?
On a 4‑blade with −10° twist at 110 KTAS, my sweet spot is about 384–386 rpm; below about 378 the 3/rev shows up in the seat, , and the extra power savings over 385 is maybe 1% vs your about 3% from 408→370. I hard‑gate droop so advance ratio mu stays ≤0.38 at that condition to preserve retreating‑side stall margin (see FAA HFH: Helicopter Flying Handbook | Federal Aviation Administration); what does your mu look like at 370?
I’m seeing my sweet spot a touch higher than @diane_r021, around 390±2 rpm at 110 KTAS; below about 380 the seat buzz shows and the retreating-side margin tightens faster than the about 1–2% power gain is worth. Quick step: do a 2‑minute sweep and log NR, μ, and vertical 3/rev, then compare to the RBS index curves in NASA TP‑2010‑216262 (IXO/XMS Detector Trade-Off Study - NASA Technical Reports Server (NTRS)); in bumps I add 3–5 kt or a click of NR to keep headroom.