## 5 Conclusions  
This paper studied the optimization of the key energy-absorbing structure of the helicopter seat based on the human-seat coupling system. The optimized key energy-absorbing structure significantly improved the energy absorption capacity and the crashworthiness of the helicopter seat. Additionally, the whole process provided a solution for the crashworthiness design of helicopter seats.  
1. Based on the aerospace standards, i.e., SAE AS8049B and CCAR-27-R2, this paper determined the conditions required for the H135 helicopter seat to complete the crashworthiness test. It also studied the estimation methods of the maximum tolerance limit of the human body and the minimum performance standard of the helicopter seat. This provides a reference for the crashworthiness evaluation of a helicopter.
2. According to the energy methods and the theories of structural mechanics, the simplified mechanical model of the human-seat coupling system of this helicopter during collision was established. The simulation results basically coincide with the results of the crashworthiness test. This shows that the crashworthiness assessment and analysis method established in this paper are reasonably effective, as they can analyze the structural characteristics of the seat and the dynamic response of the ATD during the crash more accurately.
3. The optimization design of energy-absorbing structures for crashworthiness represents a research hotspot in the engineering community. In this paper, the link between the design variables and the objective function was established to complete the optimization process by using Latin hypercube sampling, the kriging model and nonlinear transient finite element analysis techniques. After optimization, the crashworthiness of the helicopter was improved greatly and the result met the regulatory requirements. This optimization method can be easily extended to other complex structures for optimization design.
4. By comparing the previous results with the optimized results, we found that the height of the front end of the key energy-absorbing structure and the horizontal length have important effects on the energy-absorbing capacity of the structure. These two should be prioritized in the structural design process.
5. In this paper, the spine load was the only optimal object. More aspects should be given attention in the next step such as head injury, chest injury, femur injury and so on. In addition to the seat basin holder, the optimization of the round tubes in human-seat coupling can also improve the crashworthiness of helicopter seats.  
**Author Contributions:** Conceptualization, Y.L.; methodology, X.W.; software, X.L. and Z.Z.; validation, Y.C.; formal analysis, S.D.; writing--review and editing, X.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China (50705097) and Open Fund of the Postgraduate Innovation Base (Laboratory) of Nanjing University of Aeronautics and Astronautics (kfj20200725). The funder of both of them is [PERSON].  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to commercial reasons.  
**Acknowledgments:** The authors would like to thank Editor-in-Chief, Editor and anonymous Reviewers for their valuable reviews.  
**Conflicts of Interest:** The authors declare no conflict of interest.