**4. Conclusions**

The sizing of the vertical tailplane based on volume coefficients is clearly inadequate when it comes to novel powertrain concepts. The presented method allows to amend an existing preliminary design tool with a more detailed assessment of the vertical tailplane design without the need of changing the design process itself. This is performed by resizing the vertical tail with handbook methods that account for specific concepts, such as outboard positioned propellers. Within the given restrictions the research showed that the introduction of wing tip propellers has a significant influence on the sizing of the vertical tail. Out of the four configurations investigated in this study, only one configuration leads to a smaller vertical tail, reducing the VTP area by 53.7%, compared to the initial volume coefficient-based sizing of the PT2025opt configuration performed in MICADO, whilst fulfilling the necessity to counteract the residual torque resulting from the loss of one gas turbine. This leads to a reduction in OME of and 3.7% and a 4.9% lower fuel consumption over the given design mission. For the PT2025 configuration the electrification of the powertrain leads to unrealistic large vertical tailplanes that supersede the reference wing area.

The results of this work present a simple method to be integrated in the preliminary aircraft design and the necessity to do so. In our specific high-wing, T-tail configuration with wing tip propulsors, the possibility to reduce the VTP size and therefore the possibility to reduce fuel consumption and emissions of the investigated configuration was shown. As this method has the potential to improve the preliminary design of unconventional aircraft, further research should be conducted to test its suitability for different configurations, while possibly substituting the used handbook methods by advanced methods, depending on the required computation time.

**Author Contributions:** Conceptualization, A.A., A.B., E.S. and A.S.; methodology, A.A.; software, A.B.; data curation, P.S. and C.Z.; writing—original draft preparation, A.A., A.B, P.S. and C.Z.; writing—review and editing, A.A., A.B., P.S., C.Z., E.S. and A.S.; supervision, E.S. and A.S.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by Federal Ministry for Economic Affairs and Energy on the basis of a decision by the German Bundestag under Grant Agreement No. 20E1916A and 20E1916F.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** This research was conducted with data compiled by the "GNOSIS" consortium. It is yet available in various publications, this paper references. Please check the References, or contact the researchers for access to data.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

#### **Abbreviations**

The following abbreviations are used in this manuscript:

