## 4 Results: Optimized Configurations
### Airport Compatibility  
A key aspect in the introduction of a novel transport aircraft lies in the assessment of compatibility with current airport infrastructure. In particular, the main aspects to be considered in the conceptual design phase are related to limits on runway lengths for landing/take-off and dimensional compatibility with aprons. Regarding the first point, the minimum runway length, this has been addressed in the design phase for both the TW and BW hybrid-electric configurations, through the sizing of the propulsion system. In particular, within the matching chart, the take-off sizing condition has been imposed in the event of a failure of one of the two propulsive units, considering a maximum runway  
Figure 16: Pax-range envelope of optimized hybrid-electric BW (**first row**) and TW (**second row**) configurations; the plotted contour is CO\({}_{2}\) emissions (with CO\({}_{2}\) = 0 kg/kWh), and the (**last row**) reports the point-to-point difference between TW and BW.  
Figure 17: DOC contours inside the pax-range envelope for the benchmark thermal TW.  
length of 1100 m. Since this dimensional constraint has been imposed for both architectures, there are no differences between them in this regard. On the other hand, it is different when it comes to the subject of airport aprons; these are regulated by the standards of the ICAO Aerodrome Codes [53], which, among the various characteristics of the apron, regulate its maximum width, i.e., they limit the maximum wingspan of the aircraft that can utilize the apron. Table 8 shows the ICAO Aerodrome Codes and the related maximum wingspan values.  
Analyses on the availability of airport aprons show that the smaller the wingspan, i.e., the lower the ICAO code complied with, the greater the possibilities of using more airports [54], even small ones, providing the opportunity to open new routes as well. This is of key importance in the regional market, where short routes are often involved between places with small airport infrastructures [52]. In this context, as discussed above, the effective introduction of hybrid-electric propulsion introduces MTOW increases compared to corresponding state-of-the-art thermal aircraft. Therefore, the lifting surfaces required to trim the aircraft in horizontal flight are also larger than their current equivalents. This, for the TW hybrid-electric configurations results in wingspan increases; on the other hand, the BW configuration, having the lifting capabilities divided over two different surfaces, can trim the same weights with smaller wingspan. This can be seen from Figure 18, in which the planforms of the optimized TW and BW hybrid-electric aircraft described in Section 4.1 are superimposed.  
The wingspan data for the configurations in Figure 18 are reported in Table 9, where the minimum compatibility with ICAO Aerodrome Codes standards is also highlighted.  
From the data in Table 9 emerges the possibility of distributing the lifting load over two different surfaces and thus decrease the wingspan, allowing the BW configuration to be compatible with the 'B' standard in the case of the '\(23t^{\prime}\) configuration and to be always compatible with the 'C' standard for the other MTOW categories. On the other hand, the TW configuration is never compatible with the 'B' standard, and for configurations with lower fuel consumption, it is not compatible with the 'C' standard, introducing severe operating penalties due to the reduced number of aprons available for the 'D' standard, especially in the context of regional aviation.  
Figure 18: Planform comparison of optimized TW (grey line) and BW (black line) hybrid-electric configurations.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**ICAO Code** & **Wingspan (b) [m]** \\ \hline A & b \(<\) 15 \\ \hline B & 15 \(<\) b \(<\) 24 \\ \hline C & 24 \(<\) b \(<\) 36 \\ \hline D & 36 \(<\) b \(<\) 52 \\ \hline E & 52 \(<\) b \(<\) 65 \\ \hline F & 65 \(<\) b \(<\) 80 \\ \hline \hline \end{tabular}
\end{table}
Table 8: ICAO Aerodrome Codes [53].