Part II : 1950-1957
Hydrogen Tanks and Systems
 For a hydrogen-fueled airplane, the very low temperature and density of liquid hydrogen pose special design problems for tanks, pumps, lines, instrumentation, and other components in the fuel system. The special requirements imposed by hydrogen are recognized immediately by all who consider such designs and, of course, received major attention by the men of the Skunk Works. The CL-400 design divided the hydrogen tankage into three sections; the forward tank had a capacity of 67 000 liters; aft, 54 000; and center (sump), 15 000. The two main tanks were kept at 2.3 atmospheres pressure and the sump tank slightly lower for fuel transfer. In the sump was a booster pump, built by Pesco Products, that supplied liquid hydrogen to the engines at a pressure of 4.4 atmospheres. The engines were mounted at the wing tips, which meant that the liquid hydrogen had to pass through a hot wing with surface temperatures up to 436 K. The design provided a vacuum-jacketed, insulated line for this purpose.
There were many unknowns in the design of the hydrogen tanks and other fuel components, and numerous experiments were conducted to obtain more information. These were done at Fort Robertson and included half-scale models of the sump tank, the vacuum-jacketed lines for carrying hydrogen from the tanks through the hot wings to the engines, booster pumps, valves, controls, and other components. These were tested in thermal environments simulating flight conditions. Later a full-scale sump pump was built and shipped to Pratt & Whitney for their use in engine testing.