*3.7. Performance Data*

Evaluating the payload-range diagram in Figure 4, it is clear that the range TLAR are proven to be fulfilled. The aircraft can fly both the design mission of 800 km with a payload of 5300 kg as well as a maximum payload mission of 400 km. The rest of the TLAR are confirmed in Table 15. Now, the performance characteristics of HAIQU can be compared with the reference aircraft. It must be kept in mind that other criteria than the DOC specified for HAIQU may were used in the design of the reference aircraft. In Table 15, the performance characteristics of the reference aircraft [12] are displayed.

HAIQU exceeds the in the TLAR required climb rate at sea level, improving the take-off performance about 30% compared to the reference aircraft. The glide ratio is not ground breaking, which can be attributed to the short take-off distance requirement and the resulting wing design trade-off. At this point, it should be stated again that HAIQU is designed with the aim of fulfilling the specified TLAR of Table 1. This is why the target missions for HAIQU and the reference aircraft may differ and cannot always be compared directly. With a fuel flow of 132 kg/h during cruise, the lost mass in flight is much lower than for similar kerosene aircraft, such as the reference aircraft.

However, it has to be said that this flow of pure hydrogen is combined with oxygen from the air, which results in a production of several tons of water, which is released in fluid form at low temperatures. The total required energy amounts to 2360 kWh for the DOC benchmark mission, which is less than 1/3 of the required energy of the reference aircraft, leading to the significant cost reduction discussed in Section 3.5.4.

**Table 15.** Performance characteristics.


<sup>1</sup> Assuming an energy density of Jet A-1 at 42.8 MJ/kg [77] and an interpolation of the fuel mass for the DOC mission.

#### **4. Discussion**

The decrease in DOC shows a great deal of promise for a more environmentally friendly hydrogen-powered and more economical new aircraft. Recent press releases by Embraer [78] and Airbus [79] indicated that the near future of aviation is moving jointly towards fuel-cell powered aircraft for the regional market. Big players, such as Airbus, being part of the movement, aim at aircraft larger than 50 seats.

However, there are many challenges ahead that need to be overcome before the first hydrogen-powered regional aircraft can enter service. Regarding the fuel, there is currently no infrastructure at airports for storing hydrogen and refueling aircraft. There is also no sufficient production for blue or green hydrogen as of now, including the means of distribution from production facilities to consumers. Regarding the technical side, many technologies are still evolving and will need multiple years to achieve market readiness. Right now, no 1 MW superconducting electric motors for the aviation industry exist in the market, and fuel cells are still being tested.

The true impact of the thermal management system on aircraft performance has to be evaluated. From a legal point of view, procedures and criteria for the certification, production, maintenance and operation of hydrogen aircraft have to be developed. In order to be able to make more precise statements concerning the actual effects of these new technologies utilized in the proposed aircraft, more detailed studies using CFD and FEM may be considered for future investigations.

**Author Contributions:** Conceptualization, methodology, software, formal analysis, validation, writing—original draft preparation, J.E., S.L., C.M.B., J.S. and T.W.; writing—review and editing, J.E., S.L., C.M.B., J.S., T.W., J.M. and A.S.; supervision, A.S. and J.M.; funding acquisition, S.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 875551. The student team also thanks Stuttgart Airport for the financial support for both the trip to present at the EASN Conference in Barcelona as well as for the trip to Amsterdam to meet with Embraer.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to being in German language.

**Acknowledgments:** The findings presented here were studied, acquired and prepared by the student teams independently. The teams were able to obtain support from the expertise of the FUTPRINT50 Consortium. However, the statements made herein do not necessarily have the consent or agreement of the FUTPRINT50 Consortium. These represent the opinion and investigations of the author(s). Copyright © 2023, FUTPRINT50 Consortium, all rights reserved.

**Conflicts of Interest:** The authors declare no conflict of interest.
