## 3 Results and Discussions
### Segment Twist Control
The effects of 4- and 5-seg control are basically similar to those of 3-seg control. Some local load distributions are further optimized. Thus, too many control segments may not yield further benefits, but may be penalized with an increase in system complexity. For the four selected conditions of the UH-60A helicopter model, the segment twist control achieves greater power reduction than the uniform twist control, and the 2- and 3-seg control configurations are appropriate. Figure 23: Cont. Figure 22: Optimal control schedules of the segment twist control for condition B. Figure 24 shows the blade shaft moment increments of the optimal uniform control, 2- and 3-seg control relative to the baseline rotor segment control. When compared with uniform twist control, segment control reduces the blade shaft moment from 80\({}^{\circ}\) to 200\({}^{\circ}\) and from 280\({}^{\circ}\) to 360\({}^{\circ}\), but it increases the blade shaft moment from 200\({}^{\circ}\) to 280\({}^{\circ}\). Figure 25 shows the induced drag component and profile drag component of the blade shaft moment increment of the 3-seg control relative to the 2-seg control rotor. Figure 26 shows the dimensionless drag load increment distributions of the 3-seg control relative to the 2-seg control. When compared with 2-seg control, 3-seg control applies pitch down deformations from 30\({}^{\circ}\) to 100\({}^{\circ}\) on the tip segment and reduces the pitch down deformations at approximately 330\({}^{\circ}\) on the middle segment, thus gaining a reduction in induced drag loads on both the advancing side and the retreating side. Although there are differences in profile drag distribution between 2- and 3-seg control, they did not cause a significant diversity in profile power, as shown in Figures 25 and 26. In addition, a slight increase in both induced drag component and profile drag component of the blade shaft moment can be observed at approximately 210\({}^{\circ}\). The analysis shows that this situation is due to the Fourier series truncation and low precision of the optimization variables, which leads to suboptimal twist actuation in some regions. Figure 24: Blade shaft moment increments of the 2-seg control and 3-seg control relative to the baseline rotor. Figure 23: Dimensionless drag load increment (\(\Delta C_{X}Ma^{2}\)) distributions relative to the baseline rotor using the segment twist control for condition B. However, when reviewing the aerodynamic shape of the baseline blade, there are two airfoil transition sections at approximately 0.5 L and 0.85 L, and an inflection point of the pre-twist distribution is at approximately 0.92 L. These are similar to the positions of the innermost segment point and outermost segment point for the optimal segment control configurations. Thus, the optimal segment twist control configuration is related to the aerodynamic shape of the initial blade. Moreover, when observing the control schedule of the tip control segment, the 0/rev pitch down control has a large proportion in the multi-harmonic input. It is considered that the pre-twist distribution of the baseline blade is designed based on comprehensive optimization for the full flight envelope of the conventional rotor system, and it is not optimal for the active twist rotor.