The PEM fuel cell stack will be modelled starting from single-cell level to take into account the effect of the various losses: activation, ohmic and concentration. Different polarization curves will be then used for the model validation. The main goal is to design a full-hydrogen aircraft, considering also different options for the hydrogen storage. For each configuration, the optimal operating point will be defined so as to minimize the overall weight of the system. Sensitivity analysis will be also performed to evaluate the effect of the main electrochemical parameters of the fuel cell model. The influence of different weight and volume values of the FC system and hydrogen storage will be finally investigated.