flight demonstration of a Liquid HYdrogen load-bearing tank in an unmanned cargo platform

Project Information

fLHYing tank

Grant agreement ID: 101101946

DOI

10.3030/101101946

Project terminated on 22 April 2025

EC signature date 9 December 2022

Start date 1 January 2023

End date 31 December 2025

Funded under

• Climate, Energy and Mobility

Total cost

€ 3 947 691,25

EU contribution

€ 2 998 491,25

Coordinated by

PIPISTREL VERTICAL SOLUTIONS DOO PODJETJE ZA NAPREDNE LETALSKE RESITVE
Slovenia

Periodic Reporting for period 4 - fLHYing tank (flight demonstration of a Liquid HYdrogen load-bearing tank in an unmanned cargo platform)

Reporting period: 2025-01-01 to 2025-12-31

Summary of the context and overall objectives of the project

The fLHYing Tank project was conceived in response to the urgent need for lightweight, efficient, and certifiable liquid hydrogen (LH2) storage solutions in aviation - an essential enabler for achieving the EU’s climate neutrality goals.

The project aimed to design, manufacture, and flight-test a 1,000-liter, flight-load-bearing, vacuum-insulated composite LH2 tank onboard the Pipistrel Nuuva V300 cargo UAV. This approach was disruptive in several ways:

- It targeted the end-to-end development and qualification of a relevant-scale, fully composite LH2 tank.
- It proposed a fast-track flight-testing methodology using UAVs to safely accelerate the validation of low-TRL, high-risk technologies.
- It introduced a digital twin framework—a fluid-dynamic, thermal, and structural model calibrated with real flight data—to support future digitalized certification pathways for hydrogen technologies.

By focusing on rapid knowledge acquisition through real-world flight testing, the project sought to dramatically reduce the time-to-market for revolutionary hydrogen storage systems.

The fLHYing Tank project was designed to deliver strategic impact by:

- Supporting the Clean Aviation Programme’s Phase 1 goals.
- Contributing to the REPowerEU and Fit for 55 packages by enabling hydrogen-powered flight.
- Providing a scalable and certifiable LH2 storage solution for future zero-emission aircraft.

Although the project was ultimately terminated due to the unavailability of a suitable tank development partner—a result of budget and timeline constraints—it remains a highly relevant and strategically aligned initiative.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

- The requirements for the liquid hydrogen storage and distribution system were defined and finalized during the System Requirements Review.
- Comprehensive safety assessments were conducted at the aircraft level, covering liquid hydrogen handling procedures as well as ground and flight testing activities.
- Thermal, fluid-dynamic, and structural evaluations were carried out on various liquid hydrogen tank configurations, providing critical insights that informed system architecture decisions.
- Multiple architectural solutions at the system, subsystem, and component levels were proposed and systematically cross-evaluated.
- A material screening campaign was conducted to assess the permeability of composite samples following immersion in liquid hydrogen, yielding valuable data on material behavior and permeability changes due to LH2 exposure.
- The risk of rapid vacuum loss was identified as a critical concern. Technical and project-level evaluations of mitigation strategies were performed by the consortium, ultimately leading to a decision to switch to a Type III tank with proven vacuum tightness, which also necessitated a change in project - partners.
- In parallel, alternative motion testing methods were explored to supplement or replace UAV-based testing. These included helicopter-based testing (via sling load or cargo cabin), ground vehicle testing (using rail systems or cargo vans), and simulations using a 6-DOF platform (hexapod). These approaches were established as contingency options in the event UAV testing was not feasible.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

- Innovative tank system architectures were developed, accompanied by comprehensive trade-off studies.
- The layout for flight test instrumentation aimed at tank data collection, along with the associated flight test requirements, was formulated.
- The permeability of three novel composite materials for cryogenic tanks was characterized following exposure to liquid hydrogen (LH2), contributing new insights into their behavior under such conditions.
- Computational methodologies were developed, verified, and calibrated for calculating structural and thermal stresses in laminated and filament-wound composites.
- Interlaminar stresses were derived with sufficient accuracy to predict potential delamination damage.
- A reduced-order thermodynamic model was formulated to provide a more detailed representation of evaporation under static conditions.
- New insulation materials and strategies were evaluated, including low-density aerogels and various polymer foams.
- A spray model was implemented to simulate tank bunkering, incorporating several state-of-the-art heat transfer correlations.