## 1 Introduction
Numerical optimization results of localized pitch control from [PERSON] et al. [34] show further benefits for the rotor performance enhancement. The maximal power reduction of 7.61% was achieved by a single-objective optimization. With a multi-objective optimization, power reduction of 5.53% and 4/rev vibration reduction of 70.65% were simultaneously achieved. [PERSON] et al. studied the effect of spanwise varying camber actuation on rotor power and pitch link loads [24]. The spanwise varying camber resulted in a 1.4% improvement in rotor power reduction compared to the spanwise uniform camber. A multi- objective optimization for performance enhancement and vibration reduction while using a dual ACF rotor configuration was conducted [35]. A 6.7% power savings and 68% hub vibration savings are simultaneously achieved. [PERSON] studied a dual-flap configuration on vibration reduction [36]. The dual-flap configuration was at least 40% better than the single-flap configuration. The optimal deflection schedules of inboard and outboard flaps notably separated. In addition, the dual ACF configuration has been verified to be significant for blade load control. Three configurations of partial span microflaps were studied for the control of noise and vibration [37]. For the vibration reduction at the heavy BVI condition, the single-microflap configuration produced a 2-3 dB noise penalty on the carpet plane. This penalty was reduced with the dual- and five-microflap configurations. Figure 1: An illustration of the active twist rotor. Previous studies demonstrate the superiority of the refined control schedules and spanwise multi-device configuration on the rotor performance improvement. For the ATR configuration, existing studies tend to assume that the active twist control is consistent spanwise. [PERSON] et al. [38] performed a parameter analysis study on the rotor power reduction with a two-piece twist control rotor while using quasi-steady twist control and 2/rev twist control. The results have raised the prospect of the segment twist control rotor configuration. Because the ATR configuration is implemented by embedding discrete actuators into the composite structure, there is a motivation to consider the optimal segment twist control configuration with refined control schedules in order to improve the rotor performance. This optimal configuration may simultaneously improve the load distribution of the rotor disk along the circumferential and spanwise directions and obtain superior performance gains under limited drive capability of the twist actuators. The objective of this work is to investigate the effects on the performance of helicopters while using the optimal segment control of active twist rotor. The main contribution of this study is that a novel segment twist control configuration for ATR is proposed and the feasible improvement on the rotor power reduction in forward flight is assessed. The blades are divided into several active twist control segments along the span, and different control schedules are applied to each segment. A numerical model is deployed to predict the isolated rotor power in steady level flights. The mechanism of active twist control on the rotor power reduction is examined. An optimization framework that is based on genetic algorithm (GA) is established to obtain the optimal schedules and segment layouts of the segment twist control for power reduction. The load distribution of the rotor disk has been improved in both circumferential and spanwise directions with the optimal segment twist control, which is introduced in Section 3. The optimal segment twist control achieves a power reduction of 12.42% as compared with the 5.07% that is obtained while using the uniform twist control with single harmonic inputs for a medium-thrust and high-speed flight condition (\(C_{W}=0.0083\), \(\mu=0.35\)).