# 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

Table 1: Main data of \(m_{fb}\)-optimised configurations varying \(BED\) @600 nm. The trend is inverted for a \(BED\) of 500 Wh/kg because the larger the number of batteries on board (hence the possibility of supplying electrical energy in flight), the higher the benefit in terms of \(m_{\beta}\), reduction. In other terms, the level of technological maturity of batteries defines the actual feasibility of regional hybrid-electric aircraft, if benefits in terms of \(m_{\beta}\), are the performance index. In fact, as shown in Figure 3, although increasing \(W_{c}\) allows for similar on-board battery mass increases for all the values of \(BED\) considered, only the technological value predicted for 2035 provides significant fuel consumption reductions. The trend between \(m_{\beta}\) and MTOW thus points to an observation regarding the energy efficiency of the hybrid-electric aircraft. In fact, for these optimised configurations, increases in MTOW correspond to reductions in \(PREE\) for all the \(BED\) values up to the forecasted reference for the 2035, as shown in Figure 4.  
To discuss this contrast between metrics related to emissions (\(m_{\beta}\)) and those related to aircraft operating efficiency (\(PREE\)), a second set of optimisations in which the \(FoM\) to be  
Figure 4: \(PREE\) vs. MTOW varying BED, for optimisations with FoM \(\triangleq\ m_{\beta}\) @600 nm. maximized was set equal to the \(PREE\) was performed. In this context, Table 2 shows the obtained results. Even for the \(PREE\), if we consider the state of the art of the \(BED\), the optimal results tend towards configuration with a low in-flight electric power supply, and a similar trend is found for a value of the \(BED\) equal to 300 Wh/kg. For these configurations, in fact, maximizing the lift-to-drag ratio (hence maximizing the \(W/S\)) and minimizing the take-off weight coincides with minimizing the energy required for flight \(E\) and, therefore, since the payload and range are fixed, with maximizing the \(PREE\). The situation slightly varies for \(BED=500\) Wh/kg, for which the \(PREE\)-optimal configuration substantially differs from the \(m_{\beta}\)-optimal one. In fact, while exhibiting a non-negligible share of electrical power utilisation, the \(PREE\) optimum is far from that relevant to \(m_{\beta}\), and settles around much lower MTOW values. Once again, it is evident that for hybrid-electric aircraft, conflicts occur that differentiate sizing in the case of seeking solutions oriented towards reducing the fuel consumption (environmental benefits) or increasing the energy-efficiency metrics (operational benefits). To validate this hypothesis, also for the \(PREE\) optimisations, several runs were performed with the MTOW = \(W_{c}\) constraint, whose results are shown in Figure 5. In particular, for a value of the \(BED\) up to 300 Wh/kg, increasing \(W_{c}\) leads to penalisations in \(PREE\), as the main contribution in increasing MTOW results in higher energy required to perform the mission. A slightly different trend is evident for \(BED\) values equal to 400 and 500 Wh/kg, where the maximum is obtained at \(W_{c}\) larger than the minimum values. This occurs because there is a trade-off between the two different contributions to the energy required for flight because increasing \(W_{c}\) results in a larger energy demand to trim the aircraft in flight, while on the other hand, it allows for an increase in the on-board