The fLHYing tank project aims to flight-test a 1,000-liter flight-load-bearing vacuum-insulated composite LH2 tank in the Pipistrel Nuuva V300 cargo UAV. This project proposal is disruptive in several perspectives: (i) definition of requirements, design, manufacturing and qualification of a relevant-scale flight-load-bearing fully composite liquid hydrogen tank, (ii) accelerated acquisition of knowledge via flight-testing low-TRL hazardous technologies using UAVs, and (iii) effective application of the knowledge via calibration of a fluid-dynamic, thermal and structural digital twin of a composite LH2 tank using flight test data for advancement towards digitalized certification of aeronautical technologies. The fLHYing tank project covers the disruptive maturation of lightweight liquid hydrogen storage systems via the accelerated acquisition of knowledge on flight operation of LH2 tanks, as required by the demonstrator strategy of the Clean Aviation Strategic Research and Innovation Agenda. The main impact of the fLHYing tank project is the unprecedented reduction in the time-to-market of revolutionary technologies in the aeronautical industry, thanks to the ground-breaking fast-track flight testing of a relevant-scale composite LH2 storage system using a UAV, achieving comprehensive understanding of the behaviour of LH2 tanks in the flight environment within minimum timeframe, risk, and cost. This ambitious goal can be achieved within the 1st phase of the Clean Aviation Programme thanks to the fLHYing tank project.