Part II : 1950-1957

7. New Initiatives in High-Altitude Aircraft



Other Engines and Hydrogen Proposals


[122] Rae's proposal to use liquid hydrogen as an aircraft fuel was, of course, not new nor was his engine the only possibility for using it. In 1937, von Ohain found that his experimental turbojet engine worked well on gaseous hydrogen (p.73). In 1954, J.M. Wickham of Boeing studied the use of hydrogen for a strategic bomber powered by turbojets. For a subsonic cruise-supersonic dash flight, Wickham concluded that hydrogen gave a theoretical 30 percent increase in range over the use of a hydrocarbon fuel.19


Wright Field was also well aware of another type of engine capable of using liquid hydrogen which-like Rae's Rex I-used liquid oxygen for combustion independent of altitude. This was the turborocket, a combination of rocket and air-breathing engine, which went back as far as a suggestion by Goddard (p.74). During World War II, the Germans developed such an engine using a turbine, driven by decomposed hydrogen peroxide (steam and oxygen) to power an axial-flow compressor. The fuel was injected into the air stream and burned. The British had also investigated the turborocket by 1945, and Wright Field became interested after the war. Alfred M. Nelson, an analyst at Wright Field, reported his study of rocket-driven, turbinecompressor engines in December 1946 (fig. 30, top). Nelson described an engine where the rocket provides fuel-rich hot gases to power a turbine which drives a compressor. After leaving the turbine the fuel-rich gases burn in the air in the aft section of the engine. The hot gases expand through the exhaust nozzle to produce thrust. One of the best known champions of the turborocket was William C. House, who proposed a cycle in 1949 while an employee of the Aerojet Engineering Corporation.* House examined a number of bipropellants including liquid hydrogen and liquid oxygen. He apparently proposed this combination to the Air Force in September 1953 and later, but nothing came of it (fig. 30, bottom).20


With all this previous experience both in hydrogen as a fuel and in hybrid engines, why did the Air Force become so interested in Rae's proposal? The reasons came less from the technical interest of experts at Wright Field than from Air Force managers of research and development at Headquarters. They were under increasing pressure from other Air Force elements to develop means for increasing the operational altitude of aircraft. Rae's idea stirred interest because it was timely.


* Aerojet applied for and was granted a patent in Sept. 1950, but it was issued under a secrecy order because of potential military application. That order was removed and House received Patent 31110153 in Nov. 1963