## 1 Introduction
[13] tested a PEMFC model to examine the impact of water and oxygen-depleted air (ODA) on the performance of the system. It was concluded that a PEMFC can theoretically produce enough water for flights reaching a distance of 16,000 km, avoiding the need for water fill-up prior to take-off and lowering the take-off weight. [PERSON] and [PERSON] [14] tested five different types of fuel cells, namely solid oxide fuel cells, proton exchange membrane fuel cells, alkaline fuel cells, photocatalytic fuel cells, and molten-carbonate fuel cells, taking into consideration different factors for each type of fuel cell using an analytical hierarchical process. The results showed that PEM fuel cells worked effectively in small aircraft when used as an APU to create a hybrid electric aircraft. [PERSON] et al. [15] performed a design analysis for a lightweight aircraft in which the propulsion system operates with the PEMFC, and a Cri-Cri--the smallest twin-engine crewed aircraft--was chosen for system analysis and fuel cell-testing performance. The PEM fuel cell used 0.71 kg of hydrogen, and a total of 30.4 kWh of energy was consumed. Additionally, the Cri-Cri's flying duration with the PEM fuel cell was 73 min at 150 km/h. In contrast, the Cri-Cri aircraft's flying time without PEM fuel cell was only 30 min. [PERSON] and [PERSON] [16] designed a PEMFC power system to examine the feasibility of PEM fuel cells used for aircraft APUs; the fuel cell stack was sized to produce the developed design's highest specific energy. It has been suggested that reducing the weight of the hydrogen vessel, which makes up 47% of the fuel system's overall weight, will improve system overall efficiency. [PERSON] et al. [17] studied the potential limitations of using PEMFC in aircraft to increase the energy density of the fuel cell propulsion system, and for ice protection, heat exchangers and cryogenic hydrogen can be used as coolants for superconductors. Batteries are also suggested to prevent thrust loss brought by faulty fuel cell systems in emergency circumstances. [PERSON] et al. [18; 19] developed and examined a simplified mathematical model for a 1 kW self-humidifying PEM fuel cell stack for high-altitude unmanned aerial vehicle (UAV) operation. The model incorporates major thermodynamic and electric parameters involved in the operation of fuel cells under different operational conditions. [PERSON] et al. [20] developed a PEMFC to optimise the operating parameters of the stack to maximise system effectiveness for hybrid aircraft. The results showed that the PEMFC operated effectively depending on the phase of flight. [PERSON] et al. [21] devised a plan to tackle the high weight issue of SOFCs for aeroplane applications by re-designing each material of the SOFC stack to achieve efficient operations at low temperatures (below 873 K). [PERSON] et al. [22] investigated the impact of using extracted air from high altitudes on the operation and performance of a PEM fuel cell whilst maintaining a certain level of delivered power, and they aimed to determine the most adequate trade-off choice between fast response and reactant consumption of PEM fuel cell used for unmanned aerial systems (UASs). [PERSON] et al. [23] addressed major issues in using fuel cell systems in unmanned aerial vehicles (UAVs). Several hybrid fuel cell integrations with batteries, solar panels, and supercapacitors were investigated. It was found that combining fuel cells and solar cells considerably boosted the UAVs' endurance and offered a lightweight design. [PERSON] and [PERSON] [24] examined the design requirements for a UAS powered by a 1 kW PEM fuel cell for high-altitude operation and correlated them into a quantitative data model to produce a design-constraint diagram. [PERSON] and [PERSON] [25] analysed UAV performance with a fuel cell and solar cells. The performance of the flight was improved, with an increase in endurance from 470 min to 970 min. [PERSON] et al.