The Airplane - Jay Spenser [103]
After initially paying a local automotive mechanic to build test devices, von Ohain found unexpected sponsorship through the university. This financial support came from Ernst Heinkel, a German industrialist and bon vivant who had his own aircraft company. After graduating, von Ohain went to work for Heinkel Flugzeugwerke.
In 1937, von Ohain developed a prototype gas turbine that ran on hydrogen. A flightworthy engine soon followed that burned diesel fuel. The Heinkel He 178, a small research prototype, was built expressly for this experimental power plant. Late in August 1939, a week before the start of World War II, Luftwaffe test pilot Erich Warsitz took it aloft to successfully perform history’s first jet airplane flight.
In England, meantime, Royal Air Force officer Frank Whittle (later Sir Frank) had been working along parallel lines since the late 1920s. Although he started earlier and secured a landmark patent in 1930, a lack of either government or industry support prevented his ideas from taking wing until May 1941, nearly two years after von Ohain’s.
Having worked independently, the two men later became friends and happily shared credit as independent co-inventors of the jet engine. Their engines were remarkably similar overall. Both employed a centrifugal-flow compressor, a scaled-up version of existing technology employed in turbo-superchargers.
A centrifugal-flow compressor is a rotating disc with closely spaced, radially arranged scoops or turbine buckets. When this disc spins around the engine’s central shaft, these scoops gather air and throw it outward, packing it tight in the surrounding casing. Rounding the compressor disc, this compressed flow angles inward to enter combustion chambers, where it is mixed with fuel and ignites, feeding the engine’s continuous combustion.
The result is an exploding efflux that provides the jet’s thrust. Before exiting the tailpipe, this hot exhaust passes through turbine blades arrayed around the engine’s central shaft, causing the shaft to spin at high speed. This bearing-mounted shaft in turn is what drives the compressor at the front, keeping the cycle going.
Nazi Germany’s leaders passed over von Ohain’s engine and the He 280 jet fighter that Ernst Heinkel developed from it. Instead they sponsored other lines of development, notably the Messerschmitt Me 262 jet fighter with its Junkers Jumo 004 jet engines.
The Junkers Jumo 004 was the design of Dr. Anselm Franz, an Austrian engineer who ranks among the top tier of turbine-propulsion pioneers. Unlike the Whittle and von Ohain designs, Franz’s engine featured an axial-flow compressor. In this alternative design approach, air flows through multiple courses of compressor blades arranged radially around a central shaft instead of being thrown outward around a spinning disc. Consequently, axial-flow jet engines are longer and narrower than centrifugal-flow designs.
Franz’s slender engine allowed slimmer, more efficient designs that incurred less frontal-area drag. On the minus side, axial-flow engines are much more ticklish in terms of their internal airflow and are subject to sudden and damaging compressor stalls.
When a parallel BMW axial-flow engine development failed to materialize in time, Franz’s Jumo 004 was selected for both the Messerschmitt Me 262 and the Arado Ar 234, history’s first jet fighter and jet bomber, respectively. Matériel shortages saw this engine built largely out of sheet metal, which shortened its life in service to somewhere between twelve and twenty-five hours, necessitating frequent engine changes.
The United States did so well in World War II using conventional propulsion technologies that it had little incentive to pursue jets. This is ironic because Sanford Moss’ supercharger—in essence, one-third of a jet engine—had already contributed to U.S. leadership in high-temperature metal alloys and turbine fabrication.
Great Britain