A hydrogen fuel cell stack only works below roughly 90 degrees Celsius, and the radiators large enough to keep it there did not fit the airframe AeroDelft started with. The Delft student team is converting a small aircraft to run on liquid hydrogen, and every redesign meant new ducting to route air between enlarged radiators and the engine bay. With student membership constantly changing and no budget for tooling, the team needed a way to iterate duct geometry in days rather than months. Working with Materialise, they moved to selective laser sintering in a flame-retardant polyamide, printing the ducts in sections joined with alignment pins so they could be reshaped as the radiator layout changed. The parts have already passed wind-tunnel testing, and AeroDelft is preparing two test flights, first on gaseous hydrogen, then liquid, to prove the propulsion system in the air.