On Minimum Induced Power of the Helicopter Rotor

This paper describes research related to minimizing the induced power of a helicopter rotor. The influence of various parameters was studied, including advance ratio, blade twist, blade number, blade cutout, shaft angle, compressibility, stall model, trim condition and higher harmonic cyclic control inputs. Minimum induced power for ideal circulation distributions was also studied. The research was performed by applying state-of-the-art rotorcraft analyses with full-span free-vortex wake models and optimization algorithms. It was observed that the minimum induced power is considerably above the ideal at high advance ratio, roughly a factor of two at μ=0.4 and a factor of three at μ=0.5. Results suggest that even if direct tailoring of the circulation distribution were possible, the minimum induced power would not drop much beyond that achievable with ideally twisted blades and higher harmonic control.