# Aerodynamic Optimization and Characterization of a Ducted Tail for a Box-Launched Aircraft
## 1 Introduction
[32] optimizes the V-tail pitch angle of a supersonic missile with stealth characteristics and safe flight as the comprehensive optimization objectives, and uses an improved annealing algorithm to determine the optimal solution of the V-tail pitch angle. Refs. [33; 34; 35; 36] took a distributed power wing design method with chordwise loop volume as a distributed objective, compared and analyzed the influence of the power wing ducted wall length and chordwise position on the design results under the conditions of maintaining lift and pitching moment, and optimized the power wing shape based on a multi-objective genetic algorithm; the results showed that the optimization results of the optimization method had an average relative error compared with the design objective of only 5%, which verifies the effectiveness of the method. The above literature represents much research on the aerodynamics, structure, control, and aerodynamic optimization of folding wing and morphing aircrafts, but there is little research on the new non-folding tail and its aerodynamic optimization. In this paper, a ducted-tailed aircraft with a tail that does not need to be folded is designed, its tail is aerodynamically optimized, and the overall aerodynamic characteristics of the aircraft are analyzed. The specific contributions are as follows. (1) A ducted tail is designed, which does not need to be folded in the launch box and does not need to be unfolded after launch from the box; the lift generated by the ducted effect can be utilized to improve the static stability of the aircraft, and at the same time improve the reliability of the structure. (2) In order to improve the degree of linearization of the lift coefficient curve of the ducted tail, the relative positions of the tail and the fuselage are optimized. Based on the parametric model of the ducted tail and fuselage combination, the aerodynamic data set of the sample model is generated by the computational fluid dynamics method. Then, the SSA-BP approximate model between the design parameters and the lift-drag curve is established, and the design parameters are optimized based on the multi-objective genetic algorithm to achieve the best relative position of the ducted tail and fuselage. (3) Based on the optimization results of the multi-objective genetic algorithm, the combination of ducted tail and fuselage is refined to generate two optimized configurations, and the optimal configuration of this ducted tail aircraft is determined by means of aerodynamic characteristic analysis, which significantly improves the lift-to-drag ratio and static stability compared with the basic configuration. The remainder of this paper is organized as follows. In Section 2, the research object and problem concerned in this paper are stated. Section 3 states parametric modeling and numerical simulation methods for the research object. In Section 4, the general aerodynamic optimization framework of the ducted tail is described, along with the experimental design and approximate model selection. Then, the supportive optimization results are presented and discussed in Section 5. Finally, Section 6 summarizes this work and gives some conclusions.