# Aerodynamic Optimization and Characterization of a Ducted Tail for a Box-Launched Aircraft
## 5 Optimization Result Analysis
### Discussion of Aerodynamic Optimization Results for Tail Trimming  
To reduce the adverse effects caused by the abrupt change in the shape of the transition region connecting the inclined and horizontal sections of the fuselage tail, the tail shape of the fuselage was optimized based on Sample 6 by eliminating the horizontal section at the tail of the fuselage, and two optimized configurations as shown in Figure 13 were obtained. Compared with configuration b and configuration a, the rest of the parameters are the same; the main difference is that the fuselage tail is profiled to further increase the distance between the trailing edge of the tailplane and the fuselage tail to reduce the airflow interference from the fuselage to the tail. As shown in Figure 14, the lift drag coefficient, pitching moment coefficient, pressure cloud, and velocity cloud of the two optimized configurations are compared and analyzed with the help of CFD numerical simulation software under the Ma = 0.35 cruise condition to verify the feasibility of the optimization method in this paper. As shown in Figure 14, the two configurations after tail trimming optimization are compared with the lift coefficient curves, drag coefficient curves, lift-to-drag ratio curves, and pitching moment coefficient curves of sample 6. Compared with configuration b, configuration a and sample 6, the lift coefficient is significantly improved, the drag coefficient is slightly increased, the lift-to-drag ratio of configuration b is the largest in the cruise state at 6\({}^{\circ}\) angle of attack, and the pitching moment coefficient is the fastest decreasing. This comprehensively determines that the aerodynamic performance of configuration b is the best, and the aircraft's static stability is the best in the pitching direction. The above conclusions coincide with the analysis in the previous section, which verifies the reasonableness and effectiveness of the integrated optimization of the multi-objective genetic algorithm and fuselage tail trimming for the improvement of aerodynamic performance and static stability of ducted tailed aircraft. As shown in Figures 15 and 16, which show the pressure cloud diagrams of configuration a and configuration b at Ma = 0.35 cruise state, after optimization, there is a significant pressure difference between the inner and outer surfaces of the duct. As the angle of attack increases from 0\({}^{\circ}\) to 12\({}^{\circ}\), the high-pressure region on the outer surface of the duct increases slightly, and the low-pressure region on the inner surface of the duct increases significantly, resulting in an increase in the pressure difference between the inner  
Figure 13: Schematic diagram of optimized configurations. (**a**) Parameters of configuration a; (**b**) Parameters of configuration b.  
and outer surfaces of the duct. The pressure clouds are consistent with the results of the aerodynamic characterization, which leads to an increase in the lift coefficient of the tail with the increase in the angle of attack. Figure 14: Aerodynamic performance comparison of optimized configuration. (**a**) Lift coefficient comparison; (**b**) drag coefficient comparison; (**c**) lift-to-drag ratio comparison; (**d**) pitching moment coefficient comparison. Figure 15: Cont. Figure 16: Pressure cloud for configuration b. (**a**) AOA = 0\({}^{\circ}\); (**b**) AOA = 4\({}^{\circ}\); (**c**) AOA = 8\({}^{\circ}\); (**d**) AOA = 12\({}^{\circ}\). Combined with the comparative analysis results of the pressure clouds, Figures 17 and 18 further analyze the velocity clouds of configuration a and configuration b at Ma = 0.35 cruise state. In order to highlight the improvement effect of the fuselage tail shape optimization on the low-speed region of the fuselage tail, the engine jet boundary condition is not set for the fuselage tail during the numerical simulation.