**2. Materials and Methods**

In the following sections, the classical aircraft design methods build the base of the familiar design process. Moreover, the unconventional design methods for the hybridpropulsion technologies are described in detail. As this aircraft design is part of the FUTPRINT50 Aircraft Design Challenge, the guidelines [5] that were predefined by the challenge committee had to be strictly followed in order to ensure comparability between the different design proposals. Hereby, the main requirements were defined in the top level aircraft requirements (TLAR) [5] and elaborated by Eisenhut et al. [10], and these are listed in Table 1. The aim of the design process is to achieve the TLAR under the lowest possible direct operating costs (DOC).

**Table 1.** Top level aircraft requirements [5].


Using a reference aircraft facilitates the design process and improves accuracy [11]. Therefore, a market analysis with the goal of finding a proper aircraft was conducted. The regional aviation sector led to aircraft such as the Dash 8 and ATR 42. For the following design process, the concept refers to only one reference aircraft that fit the given TLAR the best. In this case, the ATR 42-600 [12] formed the most promising foundation and was, thus, selected as the reference aircraft.

A basic comparability of the ATR 42 and ATR 72 can be generally assumed under certain conditions, since the ATR 72 is merely an extended ATR 42 with an increased maximum seat capacity from 48 to 78 seats [13]. In addition, the wingspan and engine power are increased from the ATR 42 to the ATR 72 [13]. In the typical cases, the ATR 42-600 was used for reference values. However, if no reference values for the ATR 42-600 were available, relative values from the ATR 72 were used, which are still legitimate due to the scaled relationship between the two aircraft.
