Heinkel HeS 3

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The HeS 3 was the world's first operational jet engine to power an aircraft. Designed by Hans von Ohain while working at Heinkel, the engine first flew as the primary power of the Heinkel He 178 on 27 August 1939. Although successful, the engine had too little thrust to be really useful, and work started on the more powerful Heinkel HeS 8 as their first production design.

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.

A redesign started as the HeS 3b, which dispensed with the "folded" arrangement and returned to simpler flame cans for combustion. In order to keep the dimensions small, the widest part of the cans were arranged in front of the engine, the compressed air first flowing forward into the cans, and then rearward to the tubine. Although not as compact as the original design, the 3b was much simpler. Designed to run on gasoline, the fuel flow was preheated by running it over the rear roller bearing.

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, 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.

[edit] Specifications

For HeS 3b:

Dimensions: 1.48 m long, 0.93 m diameter

Weight: 360 kg

Thrust: 450 kgf (4.4 kN) @ 13,000 rpm and 800 km/h

Compression ratio: 2.8:1

Specific fuel consumption: 2.16 gal/(lb·h) [18.0 L/(kg·h)]

For HeS 6:

Weight: 420 kg

Thrust: 550 kgf (5.4 kN) @ 13,300 rpm and 800 km/h

Specific fuel consumption: 1.6 gal/(lb·h) [13.4 L/(kg·h)]

[edit] References

• German Jet Engine and Gas Turbine Development, Antony Kay, Airlife Books, 2002