Taking Off Toward a Sustainable Future

The aviation of tomorrow

Intensive research into alternatives for zero-emission air travel has been underway for years. One particularly innovative project stems from a focus project at ETH Zurich.

The vision of Cellsius is to operate aircraft in a climate-neutral, efficient, and sustainable manner in the future. The current project is implementing this using a hydrogen propulsion system. Electricity is generated in the fuel cell from hydrogen and oxygen (from the air). This electrical energy is then used by an electric motor to power the aircraft.

Swagelok Switzerland has supported the Focus Project from the very beginning with products, services, and expertise, particularly in the field of hydrogen and fluid technology, where the highest levels of safety and precision are required.

Cellsius Liquid H2 Team 2025/26

Success Story and Progress

CELLSIUS launched its first major project, the e-Sling, in 2020—a battery-powered aircraft that successfully completed its maiden flight in 2022. For about four years now, the focus has been on the H₂ project, which involves developing a hydrogen propulsion system for small aircraft. Hydrogen offers a significantly higher energy density than batteries and enables longer flight ranges. In 2023, Swagelok had the opportunity to staff a booth alongside CELLSIUS at Powerfuel Week in Lucerne and conduct a video interview with the project team at the time.

In 2024, the team presented the modified Sling chassis at the Swiss Innovation Park in Zurich; it had been adapted to accommodate H₂ tanks and featured extended wings for optimal lift. Engine and inverter tests were then conducted on the test stand, with power supplied by the fuel cell.

You can find the video of our impressions from the rollout and the inverter tests here:

Rollout 2025 and Outlook

The H₂-Sling was rolled out in October 2025. The prototype, which was nearly ready for flight, was unveiled, and a taxi run was already successfully conducted. Once all approvals have been obtained, the H₂-Sling is expected to achieve a flight time of up to 2 hours and a range of approximately 200 kilometers.

The goals for the near future are clear: The maiden flight in 2026 will confirm the H₂-Sling’s practical viability, while a long-term plan is in place to cross the Alps to test the range and performance of the hydrogen propulsion system under real-world conditions.

The project for 2025/26 is also already in the starting blocks. The focus here is on liquid hydrogen as an energy source. It has an energy density roughly three times higher than that of kerosene. This should make longer flight routes possible in the future, such as crossing the English Channel.

 

 

Technology, Safety, and Swagelok

The current team is working on the development of a cryogenic hydrogen powertrain. To meet the requirements for high pressure and extreme cold, the team is developing some of the components—such as the tank—itself. Advisors, experts, and freelancers are on hand to provide technical support.

Swagelok supports Cellsius with our expertise in hydrogen technology. Our valves, ball valves, and pressure regulators are installed in the mobile test rig and in the aircraft, in addition to the supply lines to the hydrogen tanks. To ensure that the products are installed correctly and safely, some team members completed the Swagelok Tube Fitting Installation Essentials training.

Leak tightness plays a crucial role, especially with hydrogen, the smallest molecule. To ensure safety, we rely on 316 stainless steel with elevated chromium and nickel content. This stainless steel contains at least 17% chromium and 12% nickel, exceeding the minimum requirements of ASTM and significantly minimizing the risk of hydrogen embrittlement.

Here is an overview of the products in use:

• Pressure regulators (K-Serie)

• Pressure gauge (PGI)

• Ball valves (Serie 40)

• Check Valves (Serie C)

• Full metal hoses (Serie FJ)

• Safety valves (Serie PRV)

• various pipes and fittings, as well as hand tube benders.

CELLSIUS impressively demonstrates how students, industry partners, and sponsors are working together to shape the future of aviation. Swagelok Switzerland is proud to be part of this project and will continue to report on its progress.

Further Information: www.cellsius.aero