Harry peacock said;
I still suspect that increasing rpm has an exponential increase in required torque (I'm sure there's a 'V squared' in there somewhere)
Nick sez:
Your instinct is correct, the thrust increases with the square of the rpm, and the torque varies with the rpm directly (first power)if the collective is lowered to maintain height, or with the square of the rpm if the collective is not moved. A 5% increase in rpm makes a 10% increase in thrust and torque if the collective is not changed.