One of the marketing challenges of unmanned aerial vehicles (UAVs) for various applications is enhancing flight durability. Due to the superior characteristics of proton exchange membrane fuel cells (PEMFCs), they have the potential to reach a longer flight time and higher payload. In this regard, a numerical assessment of a UAV air-cooled PEMFC is carried out using a three-dimensional (3-D), multiphase, and non-isothermal model on three flow fields, i.e., unblocked bean-shaped, blocked bean-shaped, and parallel. Then, the results of single-cell modeling are generalized to the PEMFC stack to provide the power of 2.5 kW for a UAV. The obtained results indicate that the strategy of rising air stoichiometry for cooling performs well in the unblocked bean-shaped design, and the maximum temperature along the channel length reaches 331.5 K at the air stoichiometric of 30. Further, it is found that the best performance of a 2.5 kW PEMFC stack is attained by the bean-shaped design without blockage, of which its volume and mass power density are 1.1 kW L⁻¹ and 0.2 kW kg⁻¹, respectively. It is 9.4% lighter and 6.9% more compact than the parallel flow field. Therefore, the unblocked bean-shaped design can be a good option for aerial applications.