Performance of a hybrid, fuel-cell-based power system during simulated small unmanned aircraft missions

• Aircraft mission simulations run on a small, fuel cell/battery hybrid power system.
• Significant dynamic interaction between fuel cell and battery via voltage matching.
• Total fuel consumption is independent of the rate of climb during the climb phase.
• Fuel-cell-only profile decreases fuel use but with reduced flexibility

Hybrid electric, fuel-cell-based power systems can significantly increase the endurance of small unmanned aerial systems (UAS) in comparison with that available from batteries. However, their detailed performance in realistic aircraft missions is relatively unknown, a situation that hinders optimal system selection and integration. This article presents the results of tests with a compact, hybrid fuel-cell/battery power system intended for aerospace applications. Flight simulations representative of surveillance and remote-sensing missions conducted with small UAS were created using the aerodynamic and system characteristics of a notional UAS with a 3.1 m wingspan; and the hybrid-power-system hardware was subjected to power-demand profiles for missions with different cruise speeds and climb rates. The results demonstrate that the performance of the fuel cell can deviate significantly from its steady-state polarisation curve for short periods of time and that careful selection of the mission profile (or inversely, selection of a specific fuel-cell/battery combination for a given mission) can increase overall performance and reduce fuel consumption by up to 3% by exploiting the high efficiency of the fuel cell at part-load.