# A Conceptual Design Methodology for e-VTOL Aircraft for Urban Air Mobility
## 4 Sensitivity Analyses for Design Space Exploration  
This section describes the application of the sizing procedure presented in Section 2 to a case study related to the _TiltOne_. The choice of this specific architecture lies in a peculiar combination of capabilities, which makes it worth investigation. These are:  
* the possibility to exploit the advantages of the box-wing, i.e., the minimization of induced drag for given wingspan and lift, in several ways depending on the given priorities and needs:
* to reduce the energy consumption for assigned payload-range and wingspan;
* to enhance transport capabilities (payload and/or range) for assigned wingspan, as highlighted by the results of the PARSIFAL project [76];
* to reduce the wingspan for assigned payload-range [77]. * the possibility to exploit one of the theoretical advantages of a tilt-wing system, consisting of:
* the transition phases can be performed with the fuselage in horizontal position;
* the possibility to exploit a tilt-wing system, which allows vertical take-off/landing, and hovering, but also to fly with the high aerodynamic efficiencies typical of fixed-wing aircraft when flying in cruise. As described in the introduction, these air vehicles are conceived to operate autonomously in the Urban Air Mobility sector, i.e., for the commercial transport of passengers on urban routes. For this purpose, following the studies on possible operating scenarios and the analysis of the related literature [37; 38; 39; 40], the Top Level Aircraft Requirements (TLARs) reported in Table 8 have been considered. Table 8 shows that:  
* the propulsion system adopted is totally electric;
* the number of motors/propellers selected is equal to eight, with four propellers placed on the front wing and four on the rear wing (as explained in Section 2.3);
* given the several unknowns about the future UAM scenario, it has been decided not to constrain the design with a given reference mission, but to allow the variation of mission range and the cruise speed within the intervals indicated in Table 8.  
In addition to the main requirements defined in Table 8, there are also further constraints that have a direct impact on the design of the flying machine; the main ones are summarized in Table 9, which highlights the following aspects:  
* the latest release of European regulations for Urban Air Mobility [32] has been considered to set the upper limit of MTOW equal to 3175 kg;
* a constraint on the maximum wingspan, which is fundamental when considering the compatibility and the use of \"vertiport\" facilities, has been derived from the feasibility \begin{table}
\begin{tabular}{c c} \hline \hline
**Type of Propulsion** & **Full-Electric** \\ \hline N\({}^{\circ}\) of motors/propellers & 8 \\ \hline N\({}^{\circ}\) of passengers & 4 \\ \hline Design range & [50,60] nm \\ \hline Cruise speed & [45,55] m/s \\ \hline Cruise height (AGL) & 500 m \\ \hline Diversion range & 5 nm \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Main Top Level Aircraft requirements for the box-wing tilt-wing conceptual design. studies carried out by Uber Elevate [38]; however, as the study and development of vertiport infrastructure is rapidly evolving, and currently there are no effective regulations or constraints, this constraint can be reviewed later and in more detailed stages of the design process;
* a minimum clearance between propellers (see Figure 9) has been set to ensure good efficiency of the propulsion system; in fact, as shown in [84], an overlap of propeller tips leads to an increase in the power required for flight. However, establishing the minimum distance in the conceptual design phase is a non-trivial problem that requires advanced analysis to optimise performance in both vertical and horizontal flight; therefore, a minimum distance of 0.1 m has been set as an initial design guideline. The fulfilment of general prescriptions on minimum axial and radial clearances between propellers and other aircraft components and structures have been implemented in the design process.