I would say that it depends on whether the aircraft is cleared to operate at the higher Nr. If it's not mentioned in the RFM then it's possiblely not.
However there are advantages of increasing the Nr for take off:
- Power is directly proportional to product of torque and rotor RPM. Thus higher rotor RPM means lower torque for the same power requirement with all engines operating. Or more power for the same torque, whichever way you like to see it.
- With a higher rotor RPM, the angle of attack and thus blade pitch for the same power is slightly less. At high angles of attack, this improves the lift-drag ratio of the blades.
- More RPM means more energy stored in the rotor – always a good thing if you lose power!
- In the event of losing an engine, the higher rotor RPM gives greater reaction time to pilots before lower limit of rotor RPM is encountered. Going from our theory for single engine helicopter, greater reaction time is always money in the wallet!
- The higher rotor RPM also reduces the height loss in transitioning to safe OEI flight –something significant while operating to offshore decks where this ‘drop down height’ versus height available is crucial for a safe flyaway.
- Higher rotor RPM translates to higher tail rotor energy through its gear ratio thereby enhancing tail rotor authority.
I had to google this to refresh my memory from long ago. I found it here:
https://www.linkedin.com/pulse/engin...sanjeev-kumar/