## 3 Results: Sensitivity Study
### DOC Comparison between TW and BW  
Figure 4 reports the yearly DOC computed for the TW and BW configurations designed within the sensitivity analysis. In general, the BW aircraft exhibits lower DOC compared to the corresponding TW: this result is related to three different aspects, namely DOC\({}_{Eu}\), DOC\({}_{Mu}\), and DOC\({}_{Ca}\), whose values are plotted in the breakdown of Figure 6. As indicated before (and demonstrated in [29]), BW configurations require less energy than TW to complete the same mission at the same MTOW, due to improved lift-to-drag ratio and the  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference Thermal Powered TW** & **Main Aircraft Features** & \multicolumn{2}{c}{**Design Point Performance**} \\ \hline Wingspan & 24 m & Range & 600 nm \\ \hline Length & 21.9 m & Passengers & 40 \\ \hline Wing surface & 49.2 m\({}^{2}\) & Total Fuel & 1479 kg\({}_{\text{f}}\) \\ \hline Tail surface & 6.9 m\({}^{2}\) & Block Fuel & 1155 kg\({}_{\text{f}}\) \\ \hline MTOW & 16,020 kg\({}_{\text{f}}\) & DOC & 11.77 M EUR/year \\ \hline OEW & 10,702 kg\({}_{\text{f}}\) & \(m_{CO_{2}}\) & 3.63 t/flight \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main features of the thermal-powered TW benchmark.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Design Parameter** & **Range Value** \\ \hline \(H_{P}\) & [0.1, 0.2, 0.3, 0.4, 0.5] \\ \hline \(W\)/S [kg\({}_{\text{f}}\)/m\({}^{2}\)] & [255, 265, 275, 285, 295, 305, 315, 325] \\ \hline \(\Phi_{CR}^{t}\) & [0.35, 0.40, 0.45, 0.50, 0.55] \\ \hline \(\Phi_{CL}^{t}\) & [0.35, 0.40, 0.45, 0.50, 0.55] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Range of design parameters.  
more efficient usage of hybrid-electric propulsion, as the statistical analysis of the output of the sensitivity analysis reports, in terms of energy required for the mission (see the left part of Figure 5), energy supplied by battery (see the middle part of Figure 5) and energy supplied by fuel (see the right part of Figure 5). This results in reduced energy-related costs for BWs; see the left part of Figure 6.  
Regarding maintenance and capital investment costs, these are directly related to the operating empty weight (OEW) according to the models discussed in [41; 43]. In particular, these reduce for lower values of OEW, hence providing DOC reductions in BW configurations. This aspect is highlighted in Equation (2), which shows that DOC\({}_{Ca}\) depends linearly on the weight of the airframe. A similar relationship exists for DOC\({}_{Ma}\), but it has not been reported for sake of conciseness; the reader can refer to the appendix of [42] for more details. The crew- and fee-related costs are identical, since the aircraft was  
Figure 4: Yearly DOC for BW and TW configurations.  
Figure 5: Energy required to accomplish the mission (**left**), energy required to battery pack (**center**), and energy required to fuel (**right**) for BW and TW.  
Figure 6: Breakdown of yearly DOC: energy (**left**), maintenance (**middle**), and capital (**right**).  
designed for the same top-level aircraft requirements, thus requiring the same onboard crew and being subject to the same navigation and ground operation fees.  
The structural, aerodynamic, and propulsive benefit introduced by the BW airframe hence reflect not only in block fuel consumption gains but also provide economic benefit with respect to the corresponding TW configurations.  
It is worth specifying that more adequate and up-to-date models regarding the assessment of hybrid-electric aircraft DOC are to be expected according to both the technological development of electric machines and to possible policy measures aimed at introducing specific charges on emissions resulting from the use of thermal power systems [50; 51].