## 2 Experimental Setup and Methods
### Experimental Equipment and Testing System  
We experimented with vertical tail jet control in the return flow low-speed wind tunnel of Nanjing University of Aeronautics and Astronautics. As shown in Figure 4, this is an open jet wind tunnel. The length of the test section is 1.7 m, and the width-to-height ratio of its square cross-section is 1.5 m \(\times\) 1 m, turbulence intensity in core area \(\varepsilon\) = 0.08%, noise less than 65 dB, and stable wind speed range of 5 m/s to 40 m/s. The experimental test system mainly includes a dynamic force and pressure measurement system and a particle image velocimetry (PIV) system. The measuring and PIV devices are shown in Figure 5. A base plate was set up in the experiment. In order to show the arrangement of the movement mechanism, the base plate was temporarily  
Figure 4: Schematic diagram of return flow low-speed wind tunnel. Figure 3: Definition of vertical tail model sideslip angle and rudder deflection angle. Figure 2: Vertical tail model and actuator layout diagram. removed. The force measurement experiment of the vertical tail model uses the ATI-9610 six-component strain gauge balance. The relevant parameters of the balance are shown in Table 1, and the measurement accuracy is 1% FS. The balance acquisition frequency is set to 10 Hz, and the force data are processed for time averaging to obtain the state's aerodynamic data. The lateral force coefficient is given by  
\[C_{Y}=\frac{Y}{\frac{1}{2}\rho U_{\infty}^{2}A_{ref}}, \tag{1}\]  
where Y is the vertical tail lateral force, \(\rho\) is the incoming flow density, \(U_{\infty}\) is the incoming flow velocity, and A\({}_{ref}\) is the reference area of the vertical tail model. The main objective of the actuator in this paper is to improve the flow situation on the rudder and thus improve the efficiency of the vertical tail rudder surface, rather than to control the flow of the entire vertical tail model. Therefore, only one side of the rudder is provided with a pressure tap, which is located on the same side as the oscillating jet actuator. The pressure measuring tap is located at the center section of the actuator at the semi-span position, and the pressure measuring section is perpendicular to the trailing edge of the stabilizer. The distance from the pressure measuring point at the center section of the actuator to the leading edge of the pressure measuring section is \(x=0.639c\), \(x=0.688c\), \(x=0.736c\), \(x=0.784c\), \(x=0.832c\), and \(x=0.904c\). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variable** & **Range** & **Precision (FS)** \\ \hline F\({}_{x}\) & 165 N & 1.00\% \\ F\({}_{y}\) & 165 N & 1.00\% \\ F\({}_{z}\) & 495 N & 1.00\% \\ M\({}_{x}\) & 15 N-m & 1.00\% \\ M\({}_{y}\) & 15 N-m & 1.00\% \\ M\({}_{z}\) & 15 N-m & 1.00\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: ATI balance parameters. Figure 5: Experimental layout. The pressure measurement experiment uses the surface pressure measurement system independently developed by the Flight Measurement and Control Innovation Laboratory of the NUAA, which is composed of 64 channel pressure transmitters, a National Instruments (NI) data acquisition system, a pressure measurement pipeline, etc. The pressure measurement range is 0.15 PSI (about 1034.2 Pa), the acquisition accuracy can reach 0.1 Pa, the acquisition resolution can reach 0.3 Pa, and the dynamic frequency response can reach 3 KHz. The pressure coefficient is calculated after the time-averaged processing of the surface pressure data \(P_{\mathrm{tap}}\) measured by the pressure tap. The pressure coefficient is given by  
\[C_{p}=\frac{p_{tap}-p_{\infty}}{q_{\infty}}, \tag{2}\]  
where \(P_{tap}\) is the surface pressure and \(P_{\infty}\) is the static pressure. The PIV experimental laser plane coincides with the symmetric plane of the exciter in the middle. It is perpendicular to the symmetric plane of the vertical tail model and the trailing edge of the stabilizer.