## 3 Performance Comparison
### Block Fuel Comparison
#### 3.1.1 Lifting System Structural Mass  
The statistical extrapolation of the mass breakdown of the lifting system subcomponents, i.e., the front wing (\(m_{w}^{f}\)), rear wing (\(m_{w}^{r}\)), and tip wing (\(m_{w}^{b}\)), of the configurations designed in the sensitivity analysis is reported in Figure 8. It is worth noting that the terms front and rear wing are suitable for BW architecture, whereas, in the case of TW, the term front wing refers to the main wing and the term rear wing refers to the tail. The results show:  
Figure 8: Statistical analysis of the structural mass of the lifting system for the BW and TW datasets. Figure 7: Statistical analysis of \(m_{\text{fb}}\) for BW and TW dataset. _(i) Lifting functions_: For the TW, the trim lift must be generated by the main wing only, whereas, for the BW, the trim lift is generated by both the front and rear wings; thus, the main wing of the TW, considering similar wing loadings, is larger in surface, in span, and undergoes higher bending loading than the individual horizontal wings of the BW. Furthermore, the static condition of the main wing of the TW is different than that of the BW lifting system, as the first is a cantilever structure, whereas the BW is over-constrained to the fuselage. The smaller wingspan combined with the different structural assembly, and the lower lift acting on each individual wing, allow for reducing the internal forces acting on the lifting system (e.g., bending moment) and designing thinner and lighter structural components with respect to TW. Accordingly, the BW front wing structure, which is the one that carries the largest part of the trim wing loading (on average about 60%, as demonstrated in [63]), is significantly lighter than the TW main wing; see the left part of Figure 8.  
_(ii) Longitudinal stability and trim functions_: For the TW, these functions are typically allocated to the combination of wing-tail design, whereas, for the BW, these functions are inherently provided by the horizontal wings. Hence, the TW needs an additional component with respect to the BW (i.e., the horizontal tailplane), introducing weight penalties. _(iii) Structural connections_: BW needs vertical joint tip wings to provide proper structural connections between the front and rear wings, and to provide the aerodynamic shape required for the optimal BW lift distribution. In this case, is the BW that needs an additional component with respect to the TW, hence introducing weight penalties; see the right part of Figure 8.  
The sum of the different contributions previously described turns out to generally provide overall lifting system structural weight reductions for the BW; see Figure 9. Having a less severe loading condition for the lifting system structure, and incorporating lifting, stability, and trim functions in a unique component, introduce structural benefits that overcome the penalization due to the presence of the vertical tip wings. Reductions in the lifting system structural mass, hence in the operating empty weight OEW, have a direct beneficial impact on the reduction in block fuel. Let us consider Equations (8) and (9):  
\[\text{BED}m_{b}\eta_{cc}+\text{FED}m_{b}\eta_{tc}=\ E_{fly}, \tag{8}\]  
\[\big{(}m_{b}+\ m_{fb}+\ m_{fb}+\ m_{p}\big{)}g\ +\text{OEW}=\text{MTOW} \tag{9}\]  
The fuel and the battery stored on board must provide the energy required to accomplish the mission \(E_{fly}\); looking at Equation (9), considering a fixed MTOW, it results that a higher OEW leads to a lower available mass of the energy sources (\(m_{b}+\ m_{fb}\)). A lower mass of energy sources, to allow Equation (8) to be satisfied, implies an increase in \(m_{fb}\) and a decrease in \(m_{b}\), as the fuel energy density FED is one order of magnitude higher than BED. To qualitatively assess this effect, Equations (8) and (9) have been plotted in a  
Figure 9: Comparison of the lifting system mass between BW and TW datasets.