Retrofitting of ultralight aircraft with a fuel cell power system

Hydrogen power systems are one of the main development prospects of our century in all means of transportation. Among them, the conversion of hydrogen energy in a fuel cell system guarantees the highest value of efficiency. However, fuel cells need to be coupled with a secondary electric storage system in mobility applications because of their limitations in terms of dynamic response and power density. In the present investigation, the preliminary design of a hybrid electric power system with fuel cells for an ultralight aerial vehicle is addressed with a retrofitting approach. The proposed power system includes a fuel cell, a lithium battery, and a compressed hydrogen vessel to replace the conventional piston-prop configuration while keeping the same maximum take-off mass. A simple but comprehensive procedure is used to find the size of the power system components that minimize the total mass and satisfy the target of a size below 200 L. The inputs of the parametric analysis are the hybridization ratio and the type of lithium battery. The results of the analysis revealed that fuel cell systems are suitable for the electrification of ultralight aviation if the desired endurance is higher than 30 min In this case, batteries by high power density are needed to satisfy the power requirements at take-off. For shorter flight times, a battery configuration is to be preferred and energy density is the most critical parameters for the choice of the battery. The possibility of charging the battery on-board determines a larger fuel cell and a higher consumption of hydrogen than a charge depleting strategy (+10 %) but avoid long charging times between two consecutive flights.