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thrust augmentation

Hans von Ohain

Hans Joachim Pabst von Ohain (December 14 1911 March 13 1998) was one of the inventors of jet propulsion. The engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently during the late 1930s, although credit for the first turbojet is given to Whittle, Ohain designed the first self-contained jet engine to run, and he was the first to power an all-jet aircraft. Although none of his designs entered production, his contributions to the development of the jet engine in Germany are invaluable. After the war, he met his British counterpart, Frank Whittle, and the two became good friends.

Early life and jet development

Born in Dessau, Germany, he earned a Ph.D. in Physics and Aerodynamics from the University of Göttingen, then one of the major centers for aeronautical research. During his studies, in 1933 he conceived of "an engine that did not require a propeller." After receiving his degree in 1935, Ohain became the junior assistant of Robert Wichard Pohl, then director of the Physical Institute of the University.

In 1936, while working for Pohl, von Ohain earned a patent on his version of jet engines, Process and Apparatus for Producing Airstreams for Propelling Airplanes. Unlike Frank Whittle's design, von Ohain's engine used a centrifugal compressor and turbine placed very close together, back to back, with the flame cans wrapped around the outside of the assembly. The resulting engine was even larger in diameter than Whittle's, although much shorter along the thrust axis.

While working at the University, von Ohain often took his sports car to be serviced at a local garage, Bartles and Becker. Here he met an automotive engineer, Max Hahn, and eventually arranged for him to build a model of his engine, which cost about 1,000 DM. When it was complete he took it to the University for testing, but ran into serious problems with combustion stability. Often the fuel would not burn inside the flame cans, and would instead be blown through the turbine where it would ignite in the air, shooting flames out the back and overheating the electric motor powering the compressor.

Heinkel

In February 1936, Pohl wrote to Ernst Heinkel on behalf of von Ohain, telling him of the design and its possibilities. Heinkel arranged a meeting where his engineers were able to grill von Ohain for hours, during which he flatly stated that the current "garage engine" would never work but there was nothing wrong with the concept as a whole. The engineers were convinced, and in April, von Ohain and Hahn were set up at Heinkel's works at the Marienehe airfield outside Rostock, Germany in Warnemünde.

Once moved, a study was made of the airflow in the engine, and several improvements made over a two month period. Much happier with the results, they decided to produce a completely new engine incorporating all of these changes, running on hydrogen gas. The resulting Heinkel-Strahltriebwerk 1 (HeS 1), German for Heinkel Jet Engine 1, was built by hand-picking some of the best machinists in the company, much to the chagrin of the shop-floor supervisors. Hahn, meanwhile, worked on the combustion problem, an area he had some experience in.

The engine was extremely simple, made largely of sheet metal. Construction started late in the summer of 1936, and completed in March 1937. It ran two weeks later on hydrogen, but the high temperature exhaust led to considerable "burning" of the metal. The tests were otherwise successful, and in September the combustors were replaced and the engine was run on gasoline for the first time. This proved to clog up the combustors, so Hahn designed a new version based on his soldering torch, which proved to work much better. Although the engine was never intended to be a flight-quality design, it proved beyond a doubt that the basic concept was workable.

While work on the HeS 1 continued, the team had already moved on to the design of a flight-quality design, the HeS 3. The major differences were the use of machined compressor and turbine stages, replacing the bent and folded sheet metal, and a re-arrangement of the layout to reduce the cross-sectional area of the engine as a whole by placing the flame cans in an extended gap between the compressor and turbine. The original design proved to have a turbine area that was simply too small to work efficiently, and increasing the size of the turbine meant the flame cans no longer fit in the gap correctly. A new design, the HeS 3b was proposed, which moved the flame cans out of the gap and modified their shape to allow the widest part of the cans to lie in front of the compressor's outer rim. In the 3b, compressed air was piped forward to the combustion chambers, and from there the now-hot air flowed rearward into the turbine inlet. While not as small as the original HeS 3 design, the 3b was nevertheless fairly compact. The 3b first ran July 1939 (some references say May), and was air-tested under the Heinkel He 118 dive bomber prototype. The original 3b engine soon burned out, but a second one was nearing completion at about the same time as a new test airframe, the Heinkel He 178, which first flew on August 27, 1939, the first jet powered aircraft to fly.

Work started immediately on larger versions, first the HeS 6 which was simply a larger HeS 3b, and then on a new design known as the HeS 8 which once again re-arranged the overall layout. The 8 separated the compressor and turbine, connecting them with a long shaft, placing a single annular combustion chamber between them, replacing the individual flame cans. It was intended to install the engine on the Heinkel He 280 fighter, but the airframe development progressed much more smoothly than the engine, and had to be used in gliding tests while work on the engine continued. A flight-quality HeS 8 was installed in late March 1941, followed by the first flight on April 2. Three days later the aircraft was demonstrated for a party of Nazi and RLM officials, all of whom were impressed. Full development funds soon followed.

By this point there were a number of turbojet developments taking place in Germany. Heinkel was so impressed by the concept that he had brought on Adolph Müller from Junkers, who was developing an axial compressor-powered design, renamed as the Heinkel HeS 30. Müller had left Junkers after they purchased the Junkers Motoren company, who had their own project under way, which by this time was known as the Junkers Jumo 004. Meanwhile BMW was making good progress with their own design, the BMW 003.

By early 1942 the HeS 8, officially the 109-001 (HeS 001), was still not progressing well. Meanwhile Müller's HeS 30, officially the 109-006 (HeS 006), was developing much more quickly. Both engines were still some time from being ready for production, however, while the 003 and 004 appeared to be ready to go. In early 1942 the director of jet development at the RLM, Helmut Schelp, refused further funding for both designs, and ordered Heinkel to work on a new "pet project" of his own, eventually becoming the Heinkel HeS 011. Although this was the first of Schelp's "Class II" engines to start working well, production had still not started when the war ended. Work continued on the HeS 8 for some time, but it was eventually abandoned in the spring of 1943.

After the war

In 1947 von Ohain was brought to the United States by Operation Paperclip and went to work for the United States Air Force at Wright-Patterson Air Force Base. In 1956 he was made the Director of the Air Force Aeronautical Research Laboratory and by 1975 he was the Chief Scientist of the Aero Propulsion Laboratory there.

During his work at Wright-Patterson, von Ohain continued his own personal work on various topics. In the early 1960s he did a fair amount of work on the design of gas core reactor rockets which would retain the nuclear fuel while allowing the working mass to be used as exhaust. The engineering needed for this role was also used for a variety of other "down to earth" purposes, including centrifuges and pumps. von Ohain would later use the basic mass-flow techniques of these designs to create a fascinating jet engine with no moving parts, in which the airflow through the engine created a stable vortex that acted as the compressor and turbine.

This interest in mass-flow also led von Ohain to research magnetohydrodynamics (MHD) for power generation, noting that the hot gases from a coal-fired plant could be used to extract power from their speed when exiting the combustion chamber, remaining hot enough to then power a conventional steam turbine. Thus an MHD generator could extract further power from the coal, and lead to greater efficiencies. Unfortunately this design has proven difficult to build due to a lack of proper materials, namely high-temperature non-magnetic materials that are also able to withstand the chemically active exhaust.

He also invented the idea of the "jet wing", in which air from the compressor of a jet engine is bled off to large "augmented" vents in the wings to provide lift for VTOL aircraft. A small amount of high-pressure air is blown into a venturi, which in turn sucks a much larger volume of air along with it, thus leading to "thrust augmentation". The concept was used in the Rockwell XFV-12 experimental aircraft, although the market interest in VTOL aircraft was short-lived.

During his career, von Ohain won many engineering and management awards, including (among others) the AIAA's Goddard Award, the US Air Force Exceptional Civilian Service Award, Systems Command Award for Exceptional Civilian Service, the Eugene M. Zuckert Management Award, the Air Force Special Achievement Award, and just before he retired, the Citation of Honor. In 1991 von Ohain and Whittle were jointly awarded the Charles Stark Draper Prize for their work on turbojet engines.

He retired from Wright-Patterson in 1979 and took up an associate professor position at the nearby University of Dayton. He later moved to Melbourne, Florida with his wife Hanny, where he died in 1998. He is survived by four children.

References

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