What RJMP states is absolutley correct - RRPM does increase as TAS increases and vice versa on all helicopters if you do not control it in any other way. It is a simple statement that deserves a simple answer.
As TAS increases the efficiency of the rotor disc increases as translational lift increases which for a fixed power setting requires less pitch and therefore less rotor drag so the RRPM increases.
As TAS decreases the efficiency of the rotor disc decreases as translational lift decreases which for a fixed power setting requires more pitch and therefore more rotor drag so the RRPM decreases.
Simple eh?
Autoranger
