# Aerodynamic Optimization and Characterization of a Ducted Tail for a Box-Launched Aircraft
## 6 Conclusions  
In this paper, a ducted-tailed aircraft with a tail that does not need to be folded is designed, and the aerodynamic optimization and characterization of the ducted tail for a box-launched aircraft is carried out with respect to the airflow coupling between the ducted tail and the fuselage, which results in the nonlinearities of the coefficients of lift and other problems. A ducted tail aerodynamic optimization method based on the fusion of the SSA-BP approximate model and multi-objective genetic algorithm is proposed, and the effectiveness of the method is verified by numerical simulation. On the basis of this optimization result, the ducted tail and fuselage combination body is further optimized, and the optimal configuration of this ducted tail aircraft is determined through comprehensive aerodynamic analysis. Through the above research, the following conclusions are obtained:  
(1) Based on the parametric design method, a box-launched ducted tail aircraft is designed, which avoids the need for the tail to be folded in the launching box and unfolded after launching; the lift generated by the ducted effect can be utilized to improve the pitch static stability of the aircraft in the process of flight. To effectively solve the box-launch aircraft tail folding mechanism is complex, and mechanical failure can easily be caused. Meanwhile, the parametric design of the ducted tail aircraft also provides parametric model input for subsequent aerodynamic optimization. Figure 18: Comparison of velocity cloud images between sample 6 and configuration b. (**a**) AOA = 0\({}^{\circ}\); (**b**) AOA = 4\({}^{\circ}\); (**c**) AOA = 8\({}^{\circ}\); (**d**) AOA = 12\({}^{\circ}\). (2) There is airflow coupling between the ducted tail and the fuselage, and there will be lift coefficient nonlinearity and aircraft nonlinear control problems at different angles of attack. In this paper, the relative positions of the ducted tail and fuselage are optimized by combining the SSA-BP approximate model and multi-objective genetic algorithm with the objective of improving the cruise state lift-to-drag ratio of the ducted tail and the degree of linearization of the lift-to-drag curve. After the relative position of the ducted tail and fuselage is optimized, the degree of linearization of the lift coefficient curve of the tail is significantly improved, and the lift-to-drag ratio in the cruise state is significantly improved. (3) On the basis of the above optimization, the influence of key parameters on the aerodynamic performance of the tail was analyzed by comparing the lift-drag curve, pressure cloud diagram and velocity cloud diagram. It is found that the sudden change in the shape of the transition area of the fuselage tail will cause the existence of a high-pressure area and velocity dead zone in the fuselage tail, which is not favorable to tail lift. The combination of the ducted tail and the fuselage is further shaped to generate two optimized configurations, and the optimal configuration of the ducted tail aircraft is determined by means of aerodynamic performance analysis. Compared with the basic configuration, the high-pressure area and velocity dead zone of the fuselage tail are significantly improved after the trimming optimization, and the lift-to-drag ratio and static stability of the aircraft are significantly improved, which provides a reference for the design of ducted-tailed aircraft. Conceptualization, H.J. and H.Z. ([PERSON]); methodology, H.J. ; validation, H.J. and H.Z. ([PERSON]); formal analysis, H.J. and Q.Z. ; investigation, Q.Z. ; resources, H.J. ; data curation, H.J. ; writing original draft preparation, H.J. ; writing--review and editing, H.J. and H.Z. ([PERSON]); visualization, H.J. ; supervision, H.J. All authors have read and agreed to the published version of the manuscript. This research was funded by the Special Research Assistant Program (E3290C0101). Not applicable. The data presented in this study are available on request from the corresponding author due to privacy.