# Parametric Analysis for Hybrid-Electric Regional Aircraft Conceptual Design and Development
## 3 Simulation Results and Discussion
### Battery Technology Impact on Hybrid-Electric Regional Aircraft Design
#### 3.1.1 Reference Design Range: 600 nm
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \begin{tabular}{c} \(BED\) \\ **(Wh/kg)** \\ \end{tabular} & \multirow{2}{*}{\(PREE\)} & \
\begin{tabular}{c} **MTOW** \\ **(kg\({}_{d}\))** \\ \end{tabular} & \multirow{2}{*}{\(H_{P}\)} &
\begin{tabular}{c} **W/S** \\ **(kg/m\({}^{2}\))** \\ \end{tabular} & \multirow{2}{*}{\(\[PERSON]_{cl}^{t}\)} & \multirow{2}{*}{\(\[PERSON]_{cl}^{e}\)} & \multirow{2}{*}{\(\[PERSON]_{cl}^{t}\)} & \multirow{2}{*}{\(\[PERSON]_{cl}^{e}\)} & \multirow{2}{*}{\(\[PERSON]_{cl}^{e}\)} & \multirow{2}{*}{\(\[PERSON]_{cl}^{e}\)} & \multirow{2}{*}{\(\[PERSON]_{de}^{t}\)} & \multirow{2}{*}{\(\[PERSON]_{de}^{e}\)} \\ \hline
200 & 0.859 & 16,591 & 0.084 & 325 & 0.501 & 0.910 & 0.415 & 0 & 0.326 & 0.061 \\
300 & 0.882 & 16,339 & 0.152 & 325 & 0.557 & 0.415 & 0.460 & 0 & 0.293 & 0.189 \\
400 & 0.892 & 17,393 & 0.209 & 325 & 0.496 & 0.659 & 0.473 & 0 & 0.175 & 0.572 \\
500 & 0.899 & 21,995 & 0.403 & 325 & 0.294 & 0.839 & 0.471 & 0.173 & 0.194 & 0.249 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main data of \(PREE\)-optimised configurations varying BED @600 nm. Figure 5: \(PREE\) vs. MTOW varying \(BED\), for optimisations with FoM \(\triangleq\)\(PREE\) @600 nm. battery mass and thus in a higher share of electric power supply. This aspect, for a parallel hybrid-electric powertrain, increases the total propulsive efficiency \(\eta_{p}\) defined as  
\[\eta_{p}=[(1-\lambda)\eta_{t}+\lambda\eta_{e}]\eta_{g} \tag{5}\]  
where \(\lambda\) is the ratio between the power supplied by the battery and the total supplied power [44]; while \(\eta_{t}\), \(\eta_{e}\), and \(\eta_{g}\) are the efficiencies of the thermal engine, electric motor, and gearbox, respectively. In particular, as discussed in [8], increases in \(\lambda\) (associated with increases in MTOW) imply increments of \(\eta_{p}\), as shown in Figure 6 on the left. This propulsive efficiency effect is, however, of minor significance on the overall requested flight energy for a value of the \(BED\) up to 300 Wh/kg, while it has a beneficial prevalence with respect to the increase in aircraft weight up to 22,000 kg\({}_{\text{f}}\) for the case with a value of the \(BED\) of 500 Wh/kg, where (slight) reductions of \(E\) can be observed (see the right part of Figure 6). Figure 7 shows the results in terms of \(m_{fp}\) for the \(PREE\)-optimised configurations, in which a similar trend (with respect to MTOW) to that obtained for the \(m_{fp}\)-optimised configurations (see Figure 2) is observed. Setting \(PREE\) as \(FoM\), hence, may lead to a better utilisation of on-board power sources, providing energy-efficient aircraft operations. However, this conduc  
Figure 6: Parallel hybrid–electric powertrain \(\eta\) (**left**), total energy supplied (**right**) @600 nm. Figure 7: \(m_{fp}\) vs. MTOW varying BED, for optimisations with FoM \(\triangleq\)\(PREE\) @600 nm. close to the thermal-powered aircraft if the current technology for batteries is considered and to a slightly lower-power hybridisation if the technology for 2035 is considered. This aspect does not lead to actual savings in terms of fuel consumption and hence is not an effective strategy to cut greenhouse gas emissions from regional aircraft operations. Indeed, the results here discussed highlight that a paradigm change in conceiving and developing regional hybrid-electric aircraft is necessary to reach the environmental targets for which this technology is under investigation. In fact, with current technology forecasts for 2035, it seems that accepting having a much higher MTOW (and hence energy consumption) than that of the state-of-the-art full-thermal aircraft turns out to be a necessary price to pay if actual emissions benefits are to be achieved. That conclusion is true if we consider only flight-related emissions.