## 6 Conclusions  
Aiming at the problem of poor robustness of traditional controllers under nonlinear conditions such as model uncertainty, this paper designs an improved adaptive NDI control method based on real-time aerodynamic parameter identification in the frequency domain. Firstly, the online frequency domain aerodynamic parameter identification method is introduced, including the setting of the excitation signal, recursive flight data detrending, CZT transform, and recursive identification steps. Then, the solution process of the adaptive NDI method based on real-time aerodynamic identification is introduced. Based on it, an improved NDI control method is introduced to improve the control response speed. In the final simulation part, the aerodynamic parameters are identified by the real-time identification method introduced in this paper. The identification error is within 1%, which meets the requirements of adaptive control. Then, the performance of the PID controller and adaptive NDI controller in aircraft attitude control is compared. Through quantitative comparative analysis, it is proved that the adaptive NDI controller is superior to the PID controller in terms of rising speed, response speed, and overshoot. By introducing an improved adaptive NDI controller for comparative simulation, it is concluded that the controller has better control effect, which shows the feasibility of the method introduced in this paper. The frequency domain online identification introduced in this paper can achieve accurate online identification, and on this basis, an improved adaptive NDI controller is used to achieve accurate attitude control. At the same time, because the method proposed in this paper can be recursively operated step by step, the calculation amount of online identification is reduced, which is of great significance in practical engineering application. The innovation of the method proposed in this paper is mainly to combine frequency domain identification with the improved adaptive NDI control method, to design an adaptive control method that can be realized in engineering. It can use flight data to identify and optimize the control effect of the controller in real time. This highly engineered method can be applied to the design of commercial aircraft to simplify the control system design process and save costs. At the same time, it can be applied to improve the flight controller using the conventional NDI control method to  
Figure 11: Whole Process Simulation of Improved NDI Control Based on Real-time Frequency Domain Identification. improve its control effect. This improvement has a good application prospect in some application scenarios that require high flight control quality. Conceptualization, D.Z. and G.W. ; methodology, D.Z. and G.W. ; software, D.Z. ; validation, D.Z. and Z.J. ; formal analysis, D.Z., Z.J. and G.W. ; investigation, D.Z. and Z.J. ; resources, D.Z. and Z.J. ; data curation, D.Z. and Z.J. ; writing--original draft preparation, D.Z. and G.W. ; writing--review and editing, D.Z., Z.J. and G.W. ; visualization, D.Z. and Z.J. ; supervision, D.Z. and G.W. ; project administration, D.Z. and G.W. ; funding acquisition, D.Z. All authors have read and agreed to the published version of the manuscript. This research was funded by National Natural Science Foundation of China, grant number U2141229 and foundation under grant JCJQ, grant number 2019-JCJQ-DA-001-131. Not applicable. The authors declare no conflict of interest. The following abbreviations are used in this manuscript.