## 4 Simulation and Discussion  
### Aerodynamic Characteristics Analysis  
This study mainly considered the switching between NMV ascend mode and cruise mode. During the whole switching process, the effect on aircraft is mainly reflected in the changes in aerodynamic parameters and relevant aerodynamic forces and moments; changes in wing area and mean aerodynamic chord length; and uncertainties of aircraft and unknown disturbances. Figures 4-6 show the change rules of aerodynamic parameters with Mach number and angle of attack under the condition of winglet stretch out and draw back. Among them, the red grid surface represents the change curve of the stretch out state of the winglet. The blue grid surface represents the change curve of the draw back state of the winglet. The yellow grid surface represents the change curve of the switching state between the stretch out state and the draw back state of the winglet.  
It can be seen from Figure 4 that the relationship between the lift coefficient and the angle of attack can be approximated as a line. The lift coefficient of the aircraft increases with the increase in the angle of attack, and the increase in lift in the winglet stretch out state is greater than that in the draw back state. The relationship between the lift coefficient and Mach number is as follows. When the aircraft flies at subsonic speed, the lift coefficient increases with the increase in Mach number. When the aircraft flies at hypersonic speed, the lift coefficient decreases slightly with the change in flight height and air density.  
It can be seen from Figure 5 that the relationship between the drag coefficient and the angle of attack is relatively complex without obvious rules, and the overall trend is nonlinear. When NMVs fly at subsonic speed, the drag coefficient increases with the increase in the angle of attack. When NMVs fly at hypersonic speed, the drag coefficient still increases with the increase in the angle of attack, but the increase in amplitude is smaller than that of the subsonic flight. On the whole, at the same angle of attack, the greater the Mach speed, the greater the drag coefficient, and the drag coefficient of the stretch out state is greater than that of the draw back state.  
It can be seen from Figure 6 that the relationship between the pitch moment coefficient and the angle of attack can be approximately regarded as a linear change relationship. When the NMV flight speed is less than Mach 5, the pitching moment coefficients under the stretch out state and the draw back state are less than zero. They increase with the increase in the angle of attack, and the static stability of the aircraft is enhanced. When the aircraft is flying at hypersonic velocity, especially greater than Mach 6, the pitching moment coefficient of the aircraft is positive and increases with the increase in the angle of attack.  
From the above analysis, it can be seen that the changes in the state of the winglet will lead to a series of changes in the body shape, aerodynamic parameters, etc. When designing the switching controller, it is necessary to consider not only the uncertainty and disturbance but also the change in the wing area, average aerodynamic chord length, and aerodynamic parameters. Table 3 shows the main parameters and change rules of the switching process for NMVs, where \(\lambda\) is a design parameter, \(t_{1}\) and \(t_{2}\) represent the switching time, \(C_{i,sc}\) and \(C_{i,sh}(i=L,D,M)\) represent the aerodynamic parameters of the stretch out state and the draw back state, and \(x_{1}(t)\) and \(x_{2}(t)\) represent the change rules of parameters in the switching process.  
Figure 6: (a) The change rules of pitch moment coefficient of the winglet from draw back to stretch out. (b) The change rules of pitch moment coefficient when the winglet from stretch out to draw back.