## 1 Introduction  
With the development of modern flight control technology, it is possible for aircraft to fly near stall or even post stall. Especially for fighter planes, having post stall capacity enables them to achieve tactical advantages such as rapid emplacement, taking aim first, and effectively avoiding attacks in close-range air combat, which is an important capability for advanced fighter planes. Accurately obtaining the dynamic aerodynamic parameters of the fighter plane has become the key to current advanced fighter plane design. Dynamic derivatives are an important parameter in the dynamic characteristics of aircraft and have a significant impact on the analysis of aircraft stability characteristics, flight control system design, and ballistic analysis. They can provide the data for the analysis, calculation, and design of aircraft dynamic quality, control system, and guidance system [1]. Traditional methods of obtaining dynamic derivatives include wind tunnel testing and flight testing. With the development of computer technology, efficient CFD technology has also become an important means of obtaining dynamic derivatives [2]. Many researchers have conducted research on using high-precision CFD technology to identify dynamic derivatives [3], mainly using time-domain calculation methods, including the perturbation method, coning motion method, forced vibration method, and free vibration method. The basic idea of the perturbation method is that as the vehicle makes a harmonic vibration around the reference point, its unsteady flow field can be decomposed into a linear superposition of the steady flow field at the equilibrium position and the small disturbance flow field. When using first-order approximation, the disturbance flow field can be further simplified as an Euler line equation for solving the amplitude of perturbation. This equation is a linear equation with the same coefficient matrix as the Euler equation for solving steady flow, so the same difference scheme can be used to solve it. Finally, the damping derivative for a specific axis can be obtained using the conversion formula between different axes. The coning motion method replaces the unsteady flow field in inertial frames by solving the steady flow field in noninertial frames, achieving an efficient calculation of dynamic derivatives. The forced vibration method is used to simulate the working conditions of wind tunnel testing and calculate the aerodynamic forces of the unsteady harmonic vibration, then obtain the dynamic derivatives. The free vibration method is also used to simulate the working conditions of wind tunnel testing, which is different from the forced vibration method. This method firstly gives an instantaneous incentive to the aircraft and sets specific mass parameters of the aircraft, then calculates the unsteady aerodynamic force generated by the vibration under the aircraft's own mass characteristics, and finally identifies the dynamic derivatives based on this [4]. Although the CFD simulation of dynamic derivatives has made great progress, dynamic derivatives are associated with unsteady motion, and their identification requires a lot of unsteady aerodynamic force calculation work, which seriously affects the efficiency of dynamic derivatives identification. For this purpose, researchers are committed to exploring new fast-simulation methods to obtain dynamic derivatives, mainly including the harmonic balance method in the frequency domain and the time spectrum method. Based on the Fourier series expansion, the harmonic balance method transforms the unsteady solution process of the periodic unsteady flow field into the coupled solving process of several steady flow fields, and obtains the unsteady process of the entire flow field through reconstruction. On this basis, a fast-prediction method of dynamic derivatives is established. This method has high computational efficiency, has minimal modifications to existing solving programs, and is easy to program and implement [5].