Well all this questions came to my head because of sentences as "with light helo, it would be necessary to raise coll to droop Nr" on the S 61 OEI helideck takeoff, but as Polaris said, you can find similar sentences on the AW 139; this one, "Continue the acceleration using collective to droop NR to minimum of 90% and to set 2.5min power", is from 139 clear area takeoff, with engine failure at/after TDP. It seems that in both model Nr needes to be drooped to get beter performances... And that, i think, is the main question, what improve in performance you get drooping Nr.
