## 4 Results: Optimized Configurations
### BW and TW Hybrid-Electric Aircraft Impact Assessment within the Payload-Range Envelope  
The single-point comparison considering the design point presented in Section 4.2 provides relevant indications in terms of performance differences between TW and BW. However, aircrafts most often operate far from the design point [52], and for payload-range combinations, that may be variable. Therefore, in order to provide as general a discussion of aircraft performance as possible, it is appropriate to evaluate key FoMs within the entire payload-range envelope. In [29], this was completed with regard to the block fuel analysis, as shown in Figure 11, which illustrates the fuel consumption contours for standard missions at varying passengers number (20 to 40) and range (250 to 600 nm) for the TW- and BW-optimized configurations; see Section 4.1. These charts show the substantial benefit related to the use of BW hybrid-electric aircraft, for each of the MTOW considered. If we consider MTOW values similar to those of the regional turboprop aircraft currently operating (e.g., up to 23t for the ATR 72) and analyze the differences between optimized BW and TW (see the bottom part of Figure 11), we obtain average block fuel savings up to 200 kg; these gains for the BW increase as the MTOW is increased. This result highlights again the potential fuel saving of the BW configuration, which can be extended to the entire pax-range envelope. A further relevant result lies in the capability of the BW configuration with MTOW equal to 50 \(\times\) 10\({}^{3}\) kg\({}_{t}\) to operate throughout the entire operational envelope with almost zero fuel consumption, except for the small quota required for take-off. As extensively discussed in [17], the fuel consumption at the design point is 113 kg, with the highest amount in the cruise phase; if the range reduces, fuel consumption decreases, as well in climb and cruise phases, where no fuel is burnt at the exception of the take-off phase. The trade-off between MTOW and \(m_{fb}\) is a peculiarity of hybrid-electric configurations, which by carrying more batteries, thus increasing the MTOW, allow more electrical energy to be supplied during flight, at the expense of less energy demand for fuel. However, how do these trends translate into economic and environmental impacts within the entire operating envelope? Figure 12 shows the contours of the DOC per flight within the pax-range diagram for the optimized TW and BW configurations. The contours show that the DOC trend is significantly more sensitive to the range than to the payload, as changes in range result in larger increases in the energy required for the mission. The comparison between TW and BW shows that the latter offers general economic advantages not only at the design point (see Section 4.2), but throughout the operating envelope, as reported by the DOC point-by-point differences between the BW and TW configurations; see the bottom part of Figure 12. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**DOC**} \\ \hline
**Tag** & \(\Delta\)**\%BW** & \(\Delta\)**\%TW** \\ \hline
23t & 10 & 16 \\ \hline
30t & 26 & 33 \\ \hline
40t & 47 & 54 \\ \hline
50t & 69 & 77 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of optimized hybrid-electric TW and BW and reference thermal TW considering DOC as FoM. Figure 11: Pax-range envelope of optimized hybrid-electric BW (**first row**) and TW (**second row**) configurations; the plotted contour is the block fuel, and the (**last row**) reports the point-to-point difference between TW and BW. Figure 12: Pax-range envelope of optimized hybrid-electric BW (**first row**) and TW (**second row**) configurations; the plotted contour is DOC, and the (**last row**) reports the point-to-point difference between TW and BW. As in the case of the design point, the lower cost quota for BW is mainly attributable to the lower energy demand for flight, and thus, the lower cost share of electricity and fuel.