*2.6. Iteration Over the Whole Aircraft*

A change in the size of the vertical tail has accumulating effects on the whole aircraft the structural mass, the CG change, and the drag of the aircraft. Therefore, a redesign of the aircraft is necessary to achieve a feasible configuration. This redesign, in turn, has an influence on the required size of the vertical tail. In order to capture these interrelated effects and to obtain a more accurate estimation of the necessary vertical tail size, the methods described in Section 2.4 are extended to take into account the changes in the overall aircraft design. This is performed in two steps. First, the MICADO environment is used to carry out a parametric aircraft design study on a range of fin volume coefficients for all four concept aircraft. Starting from a value of 0.0225, the volume coefficient is increased in steps of 0.02 up to 0.1625 and the resulting aircraft parameters, including among others the fin size, are put out into a data table. This parametric study also includes the fin volume coefficient of 0.0825 of the original Beechcraft 1900D. The data table mentioned before is used as a data source for the subsequent sizing loop of the vertical tail. Second, the iterative design loop for the sizing of the vertical tail which is executed as follows.

The initial iteration step uses the aircraft data from the database created before which belongs to the entry of the original fin volume coefficient of 0.0825. The dataset includes information on e.g., propeller positions and maximum takeoff thrust from the aircraft. Based on this, a new size for the vertical tail is calculated using the algorithm described in Section 2.5, taking into account the propeller positions and wiring options of the partial turboelectric propulsion system. The second and all subsequent iteration steps start with an interpolation of the aircraft data with respect to the previously determined size of the vertical tailplane and the aircraft data, obtained from the parameter study on different fin volume coefficients. Among others, this yields new propeller positions due to changes in wingspan and values for maximum takeoff thrust. As described for the first iteration step, this interpolated data is used to update the size of the vertical tailplane. This process is repeated until the area of the vertical tailplane does not change more than 0.1% between two consecutive iteration steps. The whole iteration process, including the steps from Section 2.5, can be seen in Figure 5.

**Figure 5.** Whole aircraft iteration overview.
