## 5 Conclusions  
The high-speed aerodynamic design of a low-aspect-ratio tailless configuration should be focused on improving not only lift-to-drag ratio, but also the longitudinal moment characteristics. Therefore, the aerodynamic design method aim to this issue is developed herein, the obtained conclusions are as follow:  
* By defining trimming efficiency factors, the effects of twisting wing and designing the key section airfoils on the aerodynamic performance of the low-aspect-ratio tailless configuration are analyzed and quantified. It is found that twisting the wing clockwise, fore-loading or aft-reflexing the key section airfoils will improve the longitudinal moment characteristic. Atft-reflexing is more efficient than fore-loading at tip and kink airfoils. However, twisting the wing clockwise will have obvious adverse influence on the lift-to-drag ratio.
* Based on the study, the design and collocation methods of key section airfoils for the low-aspect-ratio tailless configuration can be obtained. With the constraints of geometry, the airfoil at symmetrical plane should adopt aft-reflexing design on the upper surface, fore-loading and aft-reflexing design on the lower surface with the front of the upper surface unchanged. While the airfoils at wing sections should use fore-loading and aft-reflexing design. The magnitudes of fore-loading and aft-reflexing at each section airfoil can be achieved based on the method herein.
* According to the CFD and wind tunnel results, the configuration designed by the method is trimmed and nearly achieves the maximum lift-to-drag ratio at cruise, which is in accordance with the principle for tailless configuration. In comparison with the initial one, the trimmed configuration obtains lower zero-lift pitching moment, higher available lift-to-drag ratio, and better drag divergence characteristics with theconstraints of fixed planform parameters and loading space. In addition, the trimmed configuration shows good performance at medium-altitude maneuvering condition, low speed state.  
The study of this paper can provide a method to longitudinal trimming a low-aspect-ratio tailless configuration. However, yaw control is another difficult key issue for the low-aspect-ratio tailless configuration. Our future research will focus on combination mode of traditional control surfaces, such as elevon, spoiler-slat-deflector, and all-moving/bendable wing tip, to settle the yaw control and reduce coupling roll moment. Besides, the jet circulation control on the low-aspect-ratio tailless configuration will also be studied in the future.  
Conceptualization, B.Z., Z.L., and L.L.; methodology, Z.L.; software, Z.L.; validation, L.L.; investigation, L.L., and Z.L.; writing--original draft preparation, Z.L.; writing--review and editing, Z.L.; visualization, L.L., and Z.L.; supervision, B.Z.; funding acquisition, B.Z. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Fundamental Research Funds for the Central Universities (Nos. 3102019 JC009).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.