Mass–energy relationships in multirotor unmanned aerial vehicles powered by proton exchange membrane fuel cells: An indicator-based approach

The dynamic development of hydrogen-powered unmanned aerial vehicles (UAVs) has increased the need for consistent methods to assess their mass-energy characteristics, particularly in multirotor platforms, which are characterised by high and continuous power demand during hover-dominated operation.This study aims to identify mass-energy relationships in multirotor UAVs powered by proton exchange membrane fuel cells using an indicator-based comparative framework.The analysis was based on technical data obtained from manufacturer datasheets, technical reports, catalogues, and scientific publications, including maximum take-off weight, empty weight, payload, declared flight endurance, PEMFC rated power, hydrogen tank capacity, and storage pressure.A set of normalised indicators referenced to maximum take-off weight was used, including payload fraction, structural mass fraction, specific endurance, and PEMFC power-to-weight ratio.Pearson correlation analysis, simple linear regression, confidence intervals, and bootstrap resampling were applied to support the graphical interpretation of mass-dependent trends.The results show that most analysed platforms are characterised by structural mass fractions of 75-90% of MTOW, while payload fractions are typically within 10-25% of MTOW.Specific endurance generally falls within the range of 4-10 min/kg and shows a strong negative relationship with MTOW (r=-0.75,R^2=0.56),indicating that endurance efficiency per unit mass decreases as platform mass increases.In contrast, payload fraction and structural mass fraction showed weak or negligible linear dependence on MTOW, while the power-to-weight ratio exhibited greater dispersion, reflecting manufacturer-specific PEMFC sizing strategies.In addition, a power consistency ratio was introduced to compare estimated average power demand with PEMFC rated power and to assess the internal consistency of manufacturer-declared performance data.The proposed framework provides a first-order comparative tool for identifying mass-energy trade-offs, design constraints, and potential inconsistencies in commercial hydrogen-powered multirotor UAV platforms, rather than an experimentally validated predictive model.