Experimental study on flight characteristics of unmanned aerial vehicles powered by air-cooled proton exchange membrane fuel cells in high-altitude environments

Air-cooled proton exchange membrane fuel cells (PEMFCs) are suitable as the power source of unmanned aerial vehicles (UAVs), but their performance in high-altitude environments lacks systematic quantitative research. This study investigates the high-altitude characteristics of air-cooled PEMFCs within a parameter-controllable climatic chamber, then conducts field flight tests of a model of hydrogen-powered UAV in Xizang Autonomous Region of China. The results show that the performance of air-cooled PEMFCs declines significantly as altitude increases, caused by the reduction of ambient oxygen molar concentration. At 60 kPa, the maximum power is only 58% of that under sea-level pressure. The flight of hydrogen-powered UAV in high-altitude environments faces dual impact of reduction of stacks power and decrease of propeller lift. At 4500 m, the power required for hovering rises 30% by that of flight in plain regions. Meanwhile, the tested model of UAV requires lithium battery to sustain hovering at altitudes above 3800 m, and lithium battery is deeply involved in power supply for takeoff and maneuver flight at all test altitudes. This study provides a typical case where the discharge behavior of lithium battery is determined by the architecture of hybrid power system. Finally, the test results also show that targeted measures need to be taken to address the decline of heat dissipation and hydrogen utilization efficiency in high-altitude environments to ensure the long-endurance performance of hydrogen-powered UAV.