# Parametric Analysis for Hybrid-Electric Regional Aircraft Conceptual Design and Development
## 4 Conclusions  
The aim of this paper was to identify the feasibility boundaries of regional hybrid-electric aircraft at a conceptual stage. Battery performance, in terms of gravimetric energy density, represents a bottleneck for the effective application of hybrid-electric propulsion in transport aviation. In this paper, a sensitivity analysis in this regard was conducted by considering the design of regional hybrid-electric aircraft equipped with a parallel powertrain. There are two main conclusions that can be summarized from this sensitivity analysis of the results presented in this paper. On the one hand, a clear limitation of the design space is identified, forced by the technological maturity of the batteries, which does \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{_BED (Wh/kg)_} & \multicolumn{3}{c}{**MTOW (kg\({}_{\ell}\))**} & \multicolumn{3}{c}{_m\({}_{fb}\) (kg)_} & \multicolumn{3}{c}{_PREE_} \\ \cline{2-10}  & **400 nm** & **600 nm** & **800 nm** & **400 nm** & **600 nm** & **800 nm** & **400 nm** & **600 nm** & **800 nm** \\ \hline Full-thermal & 15,210 & 15,783 & 16,404 & 734 & 1103 & 1487 & 0.871 & 0.869 & 0.859 \\
200 & 18,607 & 17,031 & 18,277 & 718 & 1097 & 1527 & 0.851 & 0.862 & 0.828 \\
300 & 46,021 & 17,462 & 19,578 & 525 & 1073 & 1509 & 0.675 & 0.873 & 0.823 \\
400 & 47,204 & 30,116 & 20,040 & 89 & 967 & 1507 & 0.941 & 0.777 & 0.812 \\
500 & 37,488 & 50,211 & 28,977 & 10 & 525 & 1378 & 1.188 & 0.729 & 0.764 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of the comparison of main results for hybrid–electric \(m_{fb}\)-optimised regional configurations, varying _BED_ and range. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{_BED_} & \multirow{2}{*}{_m\({}_{fb}\) (kg)_} & \multirow{2}{*}{_MTOW_ (kg\({}_{\ell}\))_} & \multirow{2}{*}{_H\({}_{P}\)_} & \multicolumn{2}{c}{_W/S_ (kg/m\({}^{2}\))_} & \multirow{2}{*}{_\(\mathbf{\phi}_{cl}^{t}\)_} & \multirow{2}{*}{_\(\mathbf{\phi}_{cl}^{c}\)_} & \multirow{2}{*}{_\(\mathbf{\phi}_{cl}^{t}\)_} & \multirow{2}{*}{_\(\mathbf{\phi}_{cr}^{t}\)_} & \multirow{2}{*}{_\(\mathbf{\phi}_{cr}^{c}\)_} & \multirow{2}{*}{_\(\mathbf{\phi}_{de}^{t}\)_} & \multirow{2}{*}{_\(\mathbf{\phi}_{de}^{c}\)_} \\ \cline{1-1}
200 & 1527 & 18,277 & 0.163 & 325 & 0.493 & 0.693 & 0.438 & 0 & 0.291 & 0.122 \\
300 & 1509 & 19,578 & 0.302 & 324 & 0.409 & 0.794 & 0.518 & 0 & 0.292 & 0.131 \\
400 & 1507 & 20,040 & 0.338 & 325 & 0.520 & 0.516 & 0.530 & 0.015 & 0.088 & 0.676 \\
500 & 1378 & 28,977 & 0.337 & 325 & 0.242 & 1 & 0.349 & 0.289 & 0.135 & 0.282 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Main data of \(m_{fb}\)-optimised configurations varying _BED_ @800 nm. not allow for significant reductions in fuel consumption to be achieved unless the _BED_ value of 500 Wh/kg, at pack level, is reached. On the other hand, it emerges that there is a need to change the design paradigm of such aircraft if benefits in terms of reducing greenhouse emissions are to be effectively reached. Specifically, penalties in terms of take-off weight and overall aircraft energy efficiency should be allowed for if real benefits in terms of reducing flight-related emissions are to be achieved. Furthermore, reducing the design range, and hence the operating capability of the regional aircraft, may lead to a substantial reduction in fuel consumption and direct greenhouse gas emissions. That trade-off is crucial and needs to be deeply addressed during the initial phases of the design process of such an innovative aircraft concept. Conceptualization, K.A.S., G.P. and A.A.Q. ; methodology, G.P. and K.A.S. ; software, G.P. and K.A.S. ; formal analysis, K.A.S. and G.P. ; investigation, G.P. and K.A.S. ; data curation, G.P. and K.A.S. ; writing--original draft preparation, K.A.S. and G.P. ; writing--review and editing, A.A.Q. ; visualization, G.P. and K.A.S. ; supervision, G.P., K.A.S. and A.A.Q. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable.