Hydrogen-fueled aircraft will have a slightly lower lift-to-drag ratio (L/D) and a lower wing loading than conventionally fueled aircraft. The lower L/D results from the fact that, despite requiring only about ⅓ the number of pounds of fuel, the liquid hydrogen (LH2) requires a very large volume. It has been found advantageous to carry LH2 fuel in the fuselage, rather than in wing tanks as is the case with jet fuel, in order to minimize the surface-to-volume ratio of the tanks. The low wing loading characteristic follows from the fact that LH2-fueled aircraft have an abnormally low weight of fuel to burn off during flight. Consequently, LH2-fueled aircraft tend to have larger fuselages than otherwise. Gaseous hydrogen and helium are the only products which can be used for the final purging operation because all other gases will be liquefied upon exposure to LH2.