Heinkel HeS 1 / HeS 3 / HeS 6
In 1933, Hans von Ohain wrote his PhD thesis at the University of Göttingen on the topic of an optical microphone that could be used to record sound directly to film. Siemens bought the patent for RM 3,500, a princely sum. Ohain used the money to invest in his real interest, the gas turbine. In 1934 von Ohain contracted his mechanic, Max Hahn, to build a prototype of his concept. Later referred to as the "garage engine", it quickly burned out due to the use of low-temperature metals. Nevertheless, it was successful and piqued the interest of his professor, Robert Pohl.
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.
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.
In some ways the HeS 3 design was simply a cleanup of the original HeS 1, converted to burn liquid fuel instead of the HeS 1's hydrogen gas. von Ohain was also unhappy with the large external diameter of the HeS 1, and re-arranged the layout of the new engine to allow the parts to be "folded together" in a more compact layout.
The first HeS 3 design was generally similar to the HeS 1, using a 16-bladed centrifugal compressor supported by an 8-blade impeller to smooth out the airflow in the intake. The compressed air flowed into an annular combustion chamber arranged to lie between the compressor and turbine, which were separated much more than in the HeS 1 to allow this arrangement. The first example was bench tested around March 1938, but the arrangement led to a smaller than useful compressor and poor combustion.
The engine was completed in early 1939, and was flight-tested under one of the remaining Heinkel He 118 dive bomber prototypes. The flight tests were carried out in extreme secrecy, taking off and landing under propeller power, and only flying in the early morning before other workers had arrived. Testing proceeded smoothly, but the engine eventually burned out its turbine.
A second engine was completed just after completion of the He 178 airframe, so it was decided to move directly to full flight tests. A short hop was made on 24 August during high-speed taxi tests, followed by full flight on 27 August, piloted by Erich Warsitz, the first aircraft to fly solely under jet power. Testing continued and in November the aircraft was demonstrated to RLM officials in hopes of receiving funding for the development of a larger engine, but nothing seemed forthcoming.
Hans Mauch later told von Ohain the RLM was in fact extremely impressed, but he was concerned that Heinkel's airframe team did not have the knowledge to undertake engine development. Instead he and Helmut Schelp secretly visited a number of aircraft engine manufacturers to try to start programs there. Mauch left his position in 1939 leaving Schelp in command. Schelp was not as concerned about where development was taking place, and immediately started funding Heinkel to produce a more powerful engine.
Work on a larger version, the HeS 6, started immediately, and was tested under a Heinkel He 111 late in 1939. While successful, notably in terms of vastly improved fuel economy, the weight was considered excessive and the design was abandoned in favour of the more advanced Heinkel HeS 8.