*2.1. Overview of the Conceptual Aircraft Design Tool MICADO*

For the analysis of the aircraft, the multidisciplinary-integrated conceptual aircraft design and optimization (MICADO) environment is used [13,14]. MICADO is an extended version of the university conceptual aircraft design and optimization (UNICADO) environment [15] and was developed at the RWTH Aachen University's Institute of Aerospace Systems (ILR) in 2008.

As shown in Figure 2, the MICADO aircraft design process features an iterative part including aircraft component sizing, detailed system design and a design analysis step. The iteration is repeated until selected parameters of the aircraft, e.g., maximum takeoff mass (MTOM), operating empty mass (OME), mission fuel mass and lateral position of the aircraft's centre of gravity, do not change more than user-defined margins between two consecutive iteration steps.

As comprehensive descriptions of MICADO and its tools can be found in the previously mentioned references, the following paragraphs focus on the MICADO tools and equations most important for this study.

The volume coefficient of the vertical tail determines its area. The value of the volume coefficient is either set by the user or calculated using an existing tail geometry.

Whereas mass estimation of most aircraft components, such as fuselage, landing gear, tail plane, is performed using semi-empirical handbook methods, wing mass estimation stands out as a tool based on analytical and semi-empirical methods. This tool takes into account the effect of point masses representing propulsion system components on the resulting wing structure and mass [16]. The secondary wing structure mass and mass penalties were estimated with semi-empirical methods; however, mass penalties due to aeroelastic effects were not included. Since the tail plane and electrical conductors are the focus of this study, applied methodologies for the estimation of their masses are presented in the following. The approach for estimation of the mass of the tail surfaces is taken from [17]. The fin mass is calculated in pounds according to Equation (1) and later converted to kilograms,

$$\mathcal{W}\_{\rm fin} = 2.62 \cdot \mathcal{S}\_V + 1.5 \cdot 10^{-5} \cdot \frac{N\_{\rm nl} \cdot b\_V^3 \cdot (8.0 + 0.44 \cdot \frac{\rm MTOM}{S\_{\rm ref}})}{(t/c)\_{\rm avg} \cdot \cos^2 \Lambda\_{\rm ca}} \tag{1}$$

where *SV* is the fin area including the rudder, *Nult* the ultimate load factor, *bV* the span of the fin, *Sref* the reference wing area, (*t*/*c*)*avg* the average airfoil thickness of the fin and Λ*ea* the average sweep of the quarter chord line.

For calculation of the power cable masses according to Stückl [18], the length of the conductor using the positions of the components connected by each conductor, and the power to be transferred (in terms of current *I* and voltage *U*) by each conductor is taken into account. Moreover, for calculation of the overall conductor mass, the copper wire itself as well as insulation and sheath materials are considered. Assumptions regarding material constants and equations can be found in Table 1.


**Table 1.** Assumptions and equations for conductor design.

Within the aerodynamic performance estimation module, lift and induced drag of the clean wing configuration are calculated using the German Aerospace Centre's LIFT-ING\_LINE [19]. This program is able to consider the propeller-induced velocities on wing aerodynamics. Propeller-induced velocities are calculated for cruise conditions using a blade element momentum theory. The results are added to the LIFTING\_LINE inputs. A more detailed description of this process can be found in [16]. Remaining drag components of the lifting surfaces and the remaining aircraft components are estimated using semi-empirical handbook methods. Most important for the study at hand is the estimation of the fin's viscous drag, calculated following an approach by Raymer [20]:

$$\mathcal{C}\_{D,Fin} = \frac{\mathcal{C}\_f \cdot FF \cdot Q \cdot S\_{\text{net},Fin}}{S\_{ref}} \tag{2}$$

where *CF* is the flat-pate skin-friction drag coefficient of the fin, *FF* is the form factor of the fin, *Q* is a interference factor, *Swet* is the fin's wetted area and *Sref* is the wing's reference area.

The entire design and convergence process with the modules employed for this study is shown in Figure 2 above.
