## 4 Interference Characteristics of V-Shaped Support on BWB Aircraft  
The interference of V-shaped support on the longitudinal aerodynamic characteristics of BWB aircraft at transonic conditions is shown in Figure 5. The symbol D52_L300_L2_P15 in the figure denotes D = 52 mm, L = 300 mm, H = L2, and P = 15\({}^{\circ}\), respectively. In the figure, the existence of the V-shaped support resulted in positive lift and negative pitching moment interference, and the influence magnitude was independent of the attack angles. The drag coefficient of the BWB aircraft decreased with the existence of the V-shaped support. When the attack angle was near 0\({}^{\circ}\), the interference of the V-shaped support on the BWB aircraft was \(\Delta C_{L}\) = 0.0157, \(\Delta C_{D}\) = \(-\)0.0009, and \(\Delta C_{m}\) = \(-\)0.0044. Compared with conventional-layout aircraft (\(\Delta C_{D}\) is \(-\)0.0008\(--\)0.0030) [3; 4; 8], the interference of the drag coefficient in the current research was smaller but the influence of the pitching moment could not be neglected. Therefore, the geometric parameter of the V-shaped support had to be designed in detail to reduce the interference of the pitching moment.  
Figure 4: Computational fluid dynamics (CFD) and European Transonic Windtunnel (ETW)/ China Aerodynamics Research and Development Center (CARDC) test results comparison for the CHN-T1 aircraft (\(Ma=0.78\), \(Re=3\times 10^{6}\)): (**a**) \(C_{L}\)-\(\alpha\) curves; (**b**) \(C_{L}\)-\(C_{D}\) curves.  
Figure 5: Aerodynamic characteristics of the BWB aircraft with and without the V-shaped support (\(Ma=0.75\)): (**a**) \(C_{L}\)-\(\alpha\) curves; (**b**) \(C_{D}\)-\(\alpha\) curves; (**c**) \(C_{m}\)-\(\alpha\) curves.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **EFD-CARDC** & **EFD-ETW** & **CFD** \\ \hline \(C_{L}\) (\(\alpha=0^{\circ}\)) & 0.1251 & 0.1210 & 0.1265 \\ \(C_{D}\) (\(\alpha=0^{\circ}\)) & 0.0223 & 0.0225 & 0.0228 \\ \(C_{D,Cwise}\) (\(\alpha=2^{\circ}\)) & 0.0276 & 0.0280 & 0.0278 \\ \hline \end{tabular}
\end{table}
Table 3: Aerodynamic coefficients comparison of CHN-T1 (\(Ma=0.78\), \(Re=3\times 10^{6}\)).  
The V-shaped support extended into the BWB's fuselage through the cavity of the lower surface (as shown in Figure 2), so that the influence on the upper surface was limited. The change of pressure distribution near the cavity of the lower surface was the determinant factor of support interference, which is shown in Figure 6 (part of the lower surface near the cavity). The comparison showed that the existence of the cavity and V-shaped support resulted in a pressure increase in front of the cavity, while the original low-pressure area on the lower surface decreased (as shown in red rectangle). The rise of pressure on the lower surface increased the pressure difference between the upper surface and lower surface, resulting in a higher lift coefficient (as shown in Figure 5a). The pressure recovery of the BWB aircraft was improved so that the drag coefficient decreased (as shown in Figure 5b). The pressure interference caused by the V-shaped support was concentrated on the trailing edge of the lower surface, which resulted in a significant negative pitching moment (as shown in Figure 5c).