Junkers Jumo 004

The Junkers Jumo 004 was the world's first production turbojet engine in operational use, and the first successful axial compressor turbojet engine. Some 8,000 units were manufactured by Junkers in Germany late in World War II, powering the Messerschmitt Me 262 fighter and the Arado Ar 234 reconnaissance/bomber, along with prototypes, including the Horten Ho 229. Variants and copies of the engine were produced in Eastern Europe and the USSR for several years following the end of WWII.

Design and development

The feasibility of jet propulsion had been demonstrated in Germany in early 1937 by Hans von Ohain working with the Heinkel company. Most of the Reich Air Ministry (RLM) remained uninterested, but Helmut Schelp and Hans Mauch saw the potential of the concept and encouraged Germany's aero engine manufacturers to begin their own programmes of jet engine development. The companies remained skeptical and little new development was carried out.

In 1939 Schelp and Mauch visited the companies to check up on progress. Otto Mader, head of the Junkers Motorenwerke (Jumo) division of the large Junkers aviation firm, stated that even if the concept was useful, he had no one to work on it. Schelp responded by stating that Dr Anselm Franz, then in charge of Junkers' turbo- and supercharger development, would be perfect for the job. Franz started his development team later that year, and the project was given the RLM designation 109-004 (the 109- prefix, assigned by the RLM was common to all reaction engine projects in WWII Germany, including German WWII rocket engine designs for manned aircraft).

Franz opted for a design that was at once conservative and revolutionary. His design differed from von Ohain's in that he utilised a new type of compressor which allowed a continuous, straight flow of air through the engine (an axial compressor), recently developed by the Aerodynamische Versuchsanstalt (AVA – Aerodynamic Research Institute) at Göttingen. The axial-flow compressor not only had excellent performance, about 78% efficient in "real world" conditions, but it also had a smaller cross-section, important for high-speed aircraft. Dr. Bruno Bruckman's old assistant on the jet engine program, Dr. Österich, took over for him in Berlin, and selected the axial flow design, due to its smaller diameter; it was less than the competing axial-flow BMW 003.

On the other hand, he aimed to produce an engine that was far below its theoretical potential, in the interests of expediting development and simplifying production. One major decision was to opt for a simple combustion area using six "flame cans", instead of the more efficient single annular can. For the same reasons, he collaborated heavily on the development of the engine's turbine with Allgemeine Elektrizitäts-Gesellschaft (General Electric Company, AEG) in Berlin, and instead of building development engines, opted to begin work immediately on the prototype of an engine that could be put straight into production. Franz's conservative approach came under question from the RLM, but was vindicated when even given the developmental problems that it was to face, the 004 entered production and service well ahead of the BMW 003, its more technologically advanced but slightly lower thrust competitor (7.83 kN/1,760 lbf).

At Kolbermoor, location of the Heinkel-Hirth engine works, the post-war Fedden Mission, led by Sir Roy Fedden, found jet engine manufacturing was simpler and required lower-skill labor and less sophisticated tooling than piston engine production; in fact, most of the making of hollow turbine blades and sheet metal work on jets could be done by tooling used in making automobile body panels. Fedden himself criticized the attachment of the 004's compressor casing, which was in two halves, bolted to the half-sections of the stator assemblies.

Technical description and testing

right|thumb|Frontal view of a Jumo 004 engine mounted in a nacelle on an Me 262 fighter, showing the starter pull-start handle in the center of the intake nose cone.

thumb|right|Riedel starter, with pull-start handle & cable

The first prototype 004A, which used diesel fuel, was first tested in October 1940, though without an exhaust nozzle. It was bench-tested at the end of January 1941 to a maximum thrust of , and work continued to increase the thrust, the RLM contract having set a minimum of thrust.

Vibration problems with the compressor stators, originally cantilevered from the outside, delayed the program at this point. Max Bentele, as an Air Ministry consulting engineer with a background in turbocharger vibrations, assisted in solving the problem. straight-through combustion chambers (made from sheet steel), and a one-stage turbine with hollow blades.

Later in 1943 the 004B version suffered turbine blade failures which were not understood by the Junkers team. They focused on areas such as material defects, grain size and surface roughness. Eventually, in December, blade-vibration specialist Max Bentele was once again brought in during a meeting at the RLM headquarters. He identified that the failures were caused by one of the blades' natural frequencies being in the engine running range. His solution was to raise the frequency, by increasing the blade taper and shortening them by 1 millimetre, and to reduce the operating speed of the engine

J-2, its standard fuel, a synthetic fuel produced from coal.
Diesel oil.
Aviation gasoline; not considered desirable due to its high rate of consumption.

Costing RM10,000 for materials, the Jumo 004 also proved somewhat cheaper than the competing BMW 003, which was RM12,000, and cheaper than the Junkers 213 piston engine, which was RM35,000. Moreover, the jets used lower-skill labor and needed only 375 hours to complete (including manufacture, assembly, and shipping), compared to 1,400 for the BMW 801.

Production and maintenance of the 004 was done at the Junkers works at Magdeburg, under the supervision of Otto Hartkopf. Completed engines earned a reputation for unreliability; the time between major overhauls (not technically a time between overhaul) was thirty to fifty hours, and may have been as low as ten, though a skilled flyer could double the interval. (The competing BMW 003's was about fifty.) at the end of the Second World War, production stood at 1,500 per month.

Australian National Aviation Museum, Moorabbin Airport, Melbourne, Victoria, Australia; ANAM displays a single detached Jumo 004
Deutsches Museum, Munich, Germany; The museum displays a Jumo 004B, built in 1944
The Imperial War Museum Duxford, Cambridge, United Kingdom; Displays a sectioned Jumo 004 engine.
Luftfahrt-Museum Laatzen-Hannover, Hannover, Germany; Offering the pre-production model Jumo 004A and a cutaway model of the later Jumo 004B besides a diverse collection of aircraft.
National Air and Space Museum (NASM) of the Smithsonian Institution, Washington D.C., USA; NASM is in possession of two Jumo 004s, a complete engine (on display as of 2020) and a 'cutaway' engine (not on display or is in storage as of 2020)
National Museum of the United States Air Force, Wright-Patterson Air Force Base, Dayton, Ohio, USA; NMUSAF displays one detached Jumo 004, along with one of the few surviving Me 262s (which still retains its two 004 engines)
New England Air Museum, Bradley International Airport, Windsor Locks, CT, USA; NEAM displays a 'cutaway' engine on-loan from the NMUSAF.
The Flying Heritage & Combat Armor Museum, located at Paine Field in Everett, Washington is currently restoring an Me 262 and its accompanying Jumo 004 engines to airworthy condition. The 004s have been re-tooled to allow for greater fatigue resistance and, therefore, a longer overall engine life. As of October 2019, the restored 262 has successfully performed taxiway testing under the power of its 004 engines
The South African Air Force Museum, located at Ysterplaat, Cape Town. Partly sectioned Jumo 004

Specifications (Jumo 004B)

thumb|A Jumo 004 engine is being investigated by [[Aircraft Engine Research Laboratory engineers of the National Advisory Committee for Aeronautics in 1946]]

References

Notes

Bibliography

External links

"Design Analysis of Messerschmitt Me-262 Jet Fighter Part II – The Power Plant"
First Attempt of the 21st Century to Start an Me 262A's Restored Jumo 004B jet engine with its Riedel 2-stroke APU Unit