Ground testing and analysis of a liquid-hydrogen propulsion system for UAVs

This paper presents an experimental campaign on a complete liquid hydrogen (LH 2 ) propulsion system for small uncrewed aerial vehicles. The first part investigates the boil-off performance of five 12 L (0.85 kg) LH 2 reservoirs with different internal designs. Results show average evaporation rates of 17–37 g/h and total evaporation times of 23–50 h, corresponding to endurance of up to 50 h depending on fabrication technique and insulation design. The second part examines the integrated propulsion chain, from the LH 2 reservoir to the fuel cell, including hydrogen transfer through an instrumented line and heat exchanger. The system delivers over 14,000 Wh of electrical energy, enabling ranges up to 4,400 km for a 4 m fixed-wing UAV with flight speeds of 24–27 m/s. A first-order theoretical model is introduced to support preliminary sizing, mass estimation, and boil-off prediction. These results demonstrate clear endurance advantages of LH 2 storage over compressed hydrogen systems. • LH 2 system for UAVs enables multi-day flight with up to 50 h boil-off endurance. • Tanks with same gravimetric index show varied boil-off due to internal design differences. • Complete LH 2 propulsion chain tested, delivering over 14 kWh for long-range flight. • Simplified model aids LH 2 tank sizing, mass estimation and boil-off prediction.