## 4 Results and Discussion
### The First High-Speed Cruise Stage of Flying to the Destination  
The lift-drag ratio is an essential aspect of morphing-benefit research as it can represent the flight aerodynamic efficiency and is a key parameter to be considered when an aircraft is in cruise state. Figure 5 shows the variation of \(L/D\) with \(L/W_{0}\) of VCaCh, VCa, and BA airfoil with different trailing-edge deflection angles at \(Ma=0.734\). The effects of the trailing-edge  
Figure 4: Baseline and morphing-airfoil comparison: variation of \(L/W_{0}\) with \(AoA\) at \(Ma=0.2\). Figure 3: Pressure coefficient distribution for different grids. deflection angle of the morphing airfoil on the lift-drag ratio differ under different \(L/W_{0}\) ranges, as shown in Figure 5a. This study mainly compares the difference in lift-drag ratio under different \(L/W_{0}\) ranges throughout the designed flight stages. Therefore, Figure 5a was partially enlarged to obtain Figure 5b. The required lift range is 0.96\(\sim\)0.84\(W_{0}\) under the first high-speed cruise stage of flying to the destination. Figure 5b shows that the VCaCh morphing method can increase the lift-drag ratio whether with upward deflection or downward deflection, and the upward deflection effect is more significant. The increment of morphing airfoil that can improve the lift-drag ratio will raise with the increase in \(L/W_{0}\). VCaCh_0.4 airfoil is more excellent than VCaCh_0.8 airfoil in the range of \(L/W_{0}=0.84\)-0.91, but it is the opposite in the range of \(L/W_{0}=0.91\)-0.96. However, the VCa morphing method does not improve the lift-drag ratio under this stage, whether the trailing edge deflects upward or downward. In Table 3, the lift-drag ratios of morphing airfoil and baseline airfoil are compared and the drag decomposition is conducted when the typical \(L/W_{0}=0.95\) is selected, so that the difference in lift-drag ratio of the morphing airfoil can be compared in more detail and the drag-reduction mechanism can be analyzed. The VCaCh_0.8 airfoil improves the lift-drag ratio by about 3.07% compared with BA airfoil, but VCa_0.8 airfoil fails to increase. From the results of drag decomposition, the friction drag \(D_{\text{friction}}\) of VCaCh airfoil is greater than VCa airfoil, while the pressure drag \(D_{\text{pressure}}\) is significantly smaller than VCa when the deflection angle is the same. The pressure drag difference between the two morphing methods is larger than the friction drag difference, so the total drag \(D_{\text{total}}\) of VCaCh is smaller than that of VCa airfoil at this time, and the pressure drag is actually the reason that the total drag of VCaCh airfoil decreases compared with BA airfoil. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Airfoil** & \(AOA\) & \(D_{\text{friction}}\) & \(D_{\text{pressure}}\) & \(D_{\text{total}}\) & \(L/D\) & \(L/D\) **Increment** \\  & (°) & (**N**) & (**N**) & (**N**) & (**N**) & **(**\%)** \\ \hline BA & 2.03 & 51.68238 & 51.68238 & 103.70147 & 49.71 & 0 \\ VCaCh\({}_{-}\)0.8 & 2.34 & 53.879911 & 49.737227 & 103.61714 & 49.75 & 0.08 \\ VCaCh\({}_{-}\)0.4 & 2.1 & 54.03176 & 48.300435 & 102.33219 & 50.375 & 1.34 \\ VCaCh\({}_{0.4}\) & 1.6 & 54.310334 & 46.17522 & 100.92786 & 51.076 & 2.75 \\ VCaCh\({}_{0.8}\) & 1.35 & 54.430309 & 46.17884 & 100.60915 & 51.238 & 3.07 \\ VCa\({}_{-}\)0.8 & 2.49 & 51.373503 & 54.924219 & 106.29772 & 48.496 & \(-\)2.44 \\ VCa\({}_{-}\)0.4 & 2.26 & 51.516681 & 53.306549 & 104.87723 & 49.153 & -1.12 \\ VCa\({}_{0.4}\) & 1.8 & 51.758262 & 52.106653 & 103.90648 & 49.586 & \(-\)0.25 \\ VCa\({}_{0.8}\) & 1.59 & 51.78407 & 52.895148 & 104.67922 & 49.246 & \(-\)0.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The drag decomposition and lift-drag ratio of morphing airfoil at \(Ma=0.734\), \(L/W_{0}=0.95\). Figure 5: Baseline and morphing-airfoil comparison: variation of \(L/D\) with \(L/W_{0}\) at \(Ma=0.734\). (**a**) L/W0 = 0.66\(\sim\)0.96; (**b**) the partially enlarged figure of (a): L/W0 = 0.84\(\sim\)0.96.