Facing the Heat Barrier - NASA's History Office

Facing the Heat Barrier: A History of Hypersonics
two large quantities: gross thrust and total drag. In view of uncertainties in both
these numbers, he was unable to state with confidence that such an engine would
work. Still he did not rule it out, and his “maybe” gave Avery reason to pursue the
topic further.
Avery decided to set up a scramjet group and to try to build an engine for test in a
wind tunnel. He hired Gordon Dugger, who had worked at NACA-Lewis. Dugger’s
first task was to decide which of several engine layouts, both ducted and unducted,
was worth pursuing. He and Avery selected an external-burning configuration with
the shape of a broad upside-down triangle. The forward slope, angled downward,
was to compress the incoming airflow. Fuel could be injected at the apex, with
the upward slope at the rear allowing the exhaust to expand. This approach again
bypassed the problem of producing shock-free flow in a duct. The use of external
burning meant that this concept could produce lift as well as thrust.
Dugger soon became concerned that this layout might be too simple to be effective.
Keirsey suggested placing a very short cowl at the apex, thereby easing problems
of ignition and combustion. This new design lent itself to incorporation within the
wings of a large aircraft of reasonably conventional configuration. At low speeds the
wide triangle could retract until it was flat and flush with the wing undersurface,
leaving the cowl to extend into the free stream. Following acceleration to supersonic
speed, the two shapes would extend and assume their triangular shape, then function
as an engine for further acceleration.
Wind-tunnel work also proceeded at APL. During 1958 this center had a Mach
5 facility under construction, and Dugger brought in a young experimentalist
named Frederick Billig to work with it. His first task was to show that he too could
demonstrate supersonic combustion, which he tried to achieve using hydrogen as
his fuel. He tried electric ignition; an APL history states that he “generated gigantic
arcs,” but “to no avail.” Like the NACA-Lewis investigators, he turned to fuels that
ignited particularly readily. His choice, triethyl aluminum, reacts spontaneously,
and violently, on contact with air.
“The results of the tests on 5 March 1959 were dramatic,” the APL history continues.
“A vigorous white flame erupted over the rear of [the wind-tunnel model]
the instant the triethyl aluminum fuel entered the tunnel, jolting the model against
its support. The pressures measured on the rear surface jumped upward.” The device
produced less than a pound of thrust. But it generated considerable lift, supporting
calculations that had shown that external burning could increase lift. Later tests
showed that much of the combustion indeed occurred within supersonic regions of
the flow. 22
By the late 1950s small scramjet groups were active at NACA-Lewis, Marquardt,
and APL. There also were individual investigators, such as James Nicholls of the
University of Michigan. Still it is no small thing to invent a new engine, even as
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First Thoughts of Hypersonic Propulsion
an extension of an existing type such as the ramjet. The scramjet needed a really
high-level advocate, to draw attention within the larger realms of aerodynamics and
propulsion. The man who took on this role was Antonio Ferri.
He had headed the supersonic wind tunnel in Guidonia, Italy. Then in 1943 the
Nazis took control of that country and Ferri left his research to command a band
of partisans who fought the Nazis with considerable effectiveness. This made him a
marked man, and it was not only Germans who wanted him. An American agent,
Moe Berg, was also on his trail. Berg found him and persuaded him to come to the
States. The war was still on and immigration was nearly impossible, but Berg persuaded
William Donovan, the head of his agency, to seek support from President
Franklin Roosevelt himself. Berg had been famous as a baseball catcher in civilian
life, and when Roosevelt learned that Ferri now was in the hands of his agent, he
remarked, “I see Berg is still catching pretty well.” 23
At NACA-Langley after the war, he rose in management and became director
of the Gas Dynamics Branch in 1949. He wrote an important textbook, Elements
of Aerodynamics of Supersonic Flows (Macmillan, 1949). Holding a strong fondness
for the academic world, he took a professorship at Brooklyn Polytechnic Institute
in 1951, where in time he became chairman of his department. He built up an
aerodynamics laboratory at Brooklyn Poly and launched a new activity as a consultant.
Soon he was working for major companies, drawing so many contracts
that his graduate students could not keep up with them. He responded in 1956 by
founding a company, General Applied Science Laboratories (GASL). With financial
backing from the Rockefellers, GASL grew into a significant center for research in
high-speed flight. 24
He was a formidable man. Robert Sanator, a former student, recalls that “you
had to really want to be in that course, to learn from him. He was very fast. His
mind was constantly moving, redefining the problem, and you had to be fast to
keep up with him. He expected people to perform quickly, rapidly.” John Erdos,
another ex-student, adds that “if you had been a student of his and later worked for
him, you could never separate the professor-student relationship from your normal
working relationship.” He remained Dr. Ferri to these people, never Tony, even
when they rose to leadership within their companies. 25
He came early to the scramjet. Taking this engine as his own, he faced its technical
difficulties squarely and asserted that they could be addressed, giving examples of
approaches that held promise. He repeatedly emphasized that scramjets could offer
performance far higher than that of rockets. He presented papers at international
conferences, bringing these ideas to a wider audience. In turn, his strong professional
reputation ensured that he was taken seriously. He also performed experiments as he
sought to validate his claims. More than anyone else, Ferri turned the scramjet from
an idea into an invention, which might be developed and made practical.
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