LIQUID HYDROGEN AS A PROPULSION
Part II : 1950-1957
6. NACA Research on Hydrogen for High-Altitude
 During the period 1954-1957, the NACA-Lewis Flight Propulsion
Laboratory at Cleveland investigated liquid hydrogen as a fuel for high-altitude
aircraft and missiles. The experiments began in 1954 with an investigation of
low-pressure combustion in a single turbojet combustor, extended to other
components (tanks, pumps, heat exchangers, controls) and complete turbojet
engine systems, and culminated in the first (and only) flight experiments. Among
the many contributions:
(1) Gaseous hydrogen burns well at low pressures in a
 (2) Promotion of hydrogen as a turbojet fuel; especially the
concept that high-altitude, low-speed flight using turbojet engines demands
efficient combustion at low pressure, best provided by hydrogen; and, at the
same time, aircraft configurations for that flight regime favor large-volume
aircraft which alleviates the disadvantage of hydrogen's low
(3) Lightweight, low-loss liquid hydrogen tanks are
(4) Liquid hydrogen can be pumped satisfactorily for
turbojet engine conditions.
(5) Hydrogen requires less combustion volume than
hydrocarbons, making possible shorter and lighter engines.
(6) A complete turbojet engine for subsonic flight can be
operated with hydrogen at higher altitudes and with less fuel consumption
(mass basis) than the same engine using hydrocarbon fuels.
(7) Existing turbojet engines can be easily adapted to
(8) Flight demonstrations that liquid hydrogen can be
handled safely in ground operations and in flight.
(9) Liquid hydrogen is an excellent heat-sink for very
high-speed flight where air friction heats the vehicle surfaces.
(10) Turbojets using hydrogen give good performance at
flight speeds of Mach 4 and ramjets for flight speeds of Mach 7, with much
higher speeds feasible with the latter.
All these advantages made hydrogen appear to be the fuel of
the future for advanced air-breathing engines; but, in fact, its prospects were
already being tested, as we will see.