2.2.6. Landing Gear and Electric Green Taxiing System

There are two main options for the integration of the main landing gear in reference to other high-wing aircraft [12,32]. The first option is the integration in a belly fairing similar to the reference aircraft. The second option is the integration in the cowling of the turboprop engine as on the De Havilland Dash 8–400 [32]. The integration in the cowling is challenging due to the propulsion choice of the relatively compact electric motor instead of a gas turbine. To reduce energy use and noise on the ground, we investigated alternative forms of taxiing.

At larger European airports, an aircraft spends 10–30% of its block time taxiing [33]. The electric green taxiing system (EGTS) promises to be a great solution to increase efficiency during this phase. Electric motors have a relatively low noise output, and, locally, they emit no emissions [34]. The technology readiness level (TRL) of onboard electric taxiing systems is between TRL 6 to 7 [35]. With regenerative breaking during the taxiing phase, 15% of the energy could be recovered [36], and the lifetime of the brake system would be increased [37,38]. The utilized dimensions for an electric taxiing system were calculated with the formulas from Heinrich et al. [39].

#### 2.2.7. Mass Calculation and Center of Gravity

The individual component masses were calculated by semi-empirical equations, which were derived by Torenbeek [11]. To start the iterative calculations, first, assumptions were made with the existing data of the reference aircraft [40]. The propulsion concept eliminates the conventional turboprops; therefore, the mass of the electric motors, including cabling, is calculated by linear scaling using the required power [41]. Electric motors are scalable and adjustable within the required power [42].

The mass of the fuel cell and batteries are calculated according to the methods in Sections 2.3.1 and 2.3.4. In case the reference aircraft differs in the composite vs. total structure volume ratio, further mass reduction factors can be introduced [43]. One method for calculating mass reduction factors is to reference existing data, such as the 20% structural mass savings achieved by Boeing through the use of 50% composite materials [44]. However, there is inherent uncertainty in this extrapolation, and thus conservative values as calculated by Kolb-Geßmann [45] were adopted and are presented in Table 3.


**Table 3.** Component mass reduction factor and composite amount.

The crew is considered to consist of two pilots and one cabin crew member, which were conservatively assumed at 85 kg each [46]. According to Roskam [14], the crew is an element of the operating mass empty (OME). Furthermore, the center of gravity (CoG) of the components can be determined with the methods of Torenbeek [11]. Considering the aircraft at OME with the added max fuel mass, the maximum static margin can be determined.
