A Leaf-Vein Hydrogen Spar Architecture for Cryogenic Fuel Conditioning and Distributed Waste-Heat Rejection: Toward Low Infrared Contrast in a Long-Endurance UAV

Abstract

Hydrogen's high specific energy makes it attractive for long-endurance UAV missions. This paper investigates the thermal architecture of MARID, a proton exchange membrane (PEM) fuel-cell UAV concept. Hydrogen stored in liquid form absorbs heat at the motor mount, warms to near-ambient temperature, and enters a recirculating 50 bar loop. Fuel tapped from the loop passes through a coolant-heated jacket to the anode. Leaf-inspired networks beneath the inboard wing and V-tail skins, together with a fuselage network, reject heat over 6.86 m^2 of modeled active skin. At 3,000 m, a steady-state para-hydrogen model predicts 4.195 kW of loop rejection, about 86% of modeled waste heat, with 77 W pump input and a 9.96 K area-mean active-skin temperature rise above ambient. The 10 m planform gives L/D = 27.64 at 28.73 m/s equivalent airspeed under an assumed drag build-up with tripped cooled surfaces. For the 48-hour design mission, mass convergence predicts 200.4 kg gross, including 11.50 kg of loaded hydrogen with its unusable ullage residual and three vacuum-jacketed spherical tanks totaling 17.89 kg dry. Results depend on assumed inventory, skin conductance, and component capacities.