**1. Introduction**

Over the past 40 years, air traffic has grown 10-fold, and air cargo has grown 14-fold [1]. Despite numerous crises in the 21st century, air traffic has been growing continuously [2]. Therefore, the climate responsibility of the aviation sector is even more important than ever before. The overall goal of halving the carbon emissions by the year 2050 relative to 2000 was set by the aviation industry [3]. In order to meet the European Union (EU) Green Deal main objectives [4], an overall willingness from all parties to take new paths and design bold concepts must be present.

For reaching the goals, the aircraft technology roadmap to 2050 engages in several contributing opportunities [3]. In addition to focusing on the improvement of known technologies, the roadmap foresees the increased use of new-generation technologies from 2030 onward. The EU-funded project FUTPRINT50 focuses on the possible technologies for commercial hybrid-electric aircraft for the years 2035–2040 [5]. As part of the project and contributions to the FUTPRINT50 Aircraft Design Challenge [5], the authors of this paper designed the hybrid regional aircraft HAIQU (Hydrogen Aircraft desIgned for Quick commUting).

This aircraft design provides capacity for 50 passengers and combines the advantages of battery and fuel-cell technology in a hybrid combination. Therefore, the motivations for HAIQU are to achieve zero emissions during the whole flight mission and to bring regional aviation one step closer to a modern environment as well as to encourage future aircraft

**Citation:** Eissele, J.; Lafer, S.; Mejía Burbano, C.; Schließus, J.; Wiedmann, T.; Mangold, J.; Strohmayer, A. Hydrogen-Powered Aviation—Design of a Hybrid-Electric Regional Aircraft for Entry into Service in 2040. *Aerospace* **2023**, *10*, 277. https://doi.org/ 10.3390/aerospace10030277

Academic Editor: Dimitri Mavris

Received: 2 February 2023 Revised: 1 March 2023 Accepted: 6 March 2023 Published: 11 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

designs. Using liquid hydrogen to approach net zero emissions is based on the production method of liquid hydrogen [6]. Depending on the method of production, hydrogen is labeled with different colors depending on the method of production [6,7].

Indeed, green hydrogen is the only climate-neutral type [7,8]. However, the amount of renewable energy required to produce green hydrogen in large quantities is enormous [9]. To ensure the efficiency and effectiveness of the aircraft design, various methods are utilized during the design process, which are outlined in Section 2. The trade-off studies and their results are summarized in Section 3. Finally, in Section 4, the advantages and disadvantages of the aircraft design are discussed to provide a comprehensive understanding of the design's strengths and limitations.
