Junkers Jumo 004

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Cutaway example of a Junkers Jumo 004 jet engine at the National Museum of the U.S. Air Force, Wright-Patterson AFB, Ohio.

The Jumo 004 was the world's first turbojet engine in production and operational use, and the first successful axial compressor jet engine ever built. Some 8,000 units were manufactured by Junkers in Germany during late World War II and powered the Messerschmitt Me 262, Horten Ho 229 and Arado Ar 234 aircraft. Variants of the engine were produced in Eastern Europe in the years following the war.

[edit] History

The practicality of jet propulsion had been demonstrated in Germany in early 1937 by Hans von Ohain working with the Heinkel company. Most of the 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. Eventually in 1939 Otto Mader, head of Junkers Motoren (Jumo), 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 was common to all jet projects).

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 a high-speed aircraft design.

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 Elektricitäts-Gesellschaft (AEG - General Electric Company) 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 its more technologically advanced competitor, the BMW 003.

[edit] Design

Frontal view of a Jumo 004 engine mounted in a nacelle on an Me 262 fighter

The first prototype 004A ran in spring 1940, and in January the following year was brought up to full thrust, 4.2 kN. Vibration problems with the compressor blades delayed the program at this point, until a new stator design by Max Bentele solved the problem. With the new stators in place the engine developed 5.9 kN in August, and passed a 10-hour endurance run at 9.8 kN in December. The first flight test took place on March 15 1942, when a 004A was carried aloft by a Messerschmitt Bf 110. On July 18, one of the prototype Messerschmitt Me 262s flew for the first time under jet power from its 004 engines, and the 004 was ordered into production by the RLM to the extent of 80 engines.

The 004A was strictly a test-bed, unsuitable for mass production due to its solid, and thus heavy, construction and considerable use of expensive high-temperature metals in the "hot section". For production, the 004B turned to air cooling instead, using hollow turbine blades made of inexpensive steel, cooled by compressed air "bled" from the compressor. The first production versions weighed 100 kg less than the 004A's, and in 1943 had passed several 100 hour tests.

Later in 1943 a series of engines suffered vibration problems, and solutions dragged on. Eventually, in December, Max Bentele was once again brought in during a meeting at the RLM headquarters, where he suggested several seemingly small changes to change the natural frequencies of the turbine blades, and a slight reduction in operational rpm from 9,000 to 8,700. This cured the problem, but it was not until early 1944 that full production could finally begin. These setbacks were the principal factor delaying the Luftwaffe's introduction of the Me 262 into squadron service.

Given the lower-quality steels used in the 004B, these engines typically only had a service life of some 10-25 hours, perhaps twice this in the hands of a skilled pilot. Another shortcoming of the engine, common to all early turbojets, was its sluggish throttle response. Worse, it was fairly easy to inject too much fuel into the engine by throttling up too quickly, allowing heat to build up before the cooling air could remove it. This led to softening of the turbine blades, and was a major cause for engine failures. Nevertheless, it made jet power for combat aircraft a reality for the first time.

One interesting feature of the 004 was the starter system, which consisted of a Riedel 10 hp (7 kW) 2-stroke motorcycle engine hidden in the intake. A hole in the extreme nose of the centrebody contained a pull-handle which started the piston engine, which in turned spun up the turbine. Two small gasoline tanks were fitted in the annular intake.

The exhaust area of the 004 even featured a variable geometry nozzle, which had a special restrictive body nicknamed the Zwiebel (German for onion, due to its shape when seen from the side) which had a roughly 40 cm (16 inch) fore-and-aft travel to vary the jet exhaust's cross-sectional area for thrust control.

Avia M-04

Tumansky RD-10

A number of more advanced versions were in development at the end of the war. The 004C included an afterburner for increased thrust, but was not built. The 004D improved fuel efficiency with a two-stage fuel injector, and introduced a new throttle control that avoided dumping too much fuel into the engine during throttle-ups. The 004D had passed testing and was ready to enter production in place of the 004B, when the war ended. The 004E was a 004D model with an improved exhaust area for better altitude performance.

A much more advanced model based on the same basic systems was also under development as the Jumo 012. The 012 was based on a "two-spool" system, in which two turbines, spinning at different speeds, drove two separate sections of the compressor for more efficiency. In a jet engine the compressor typically uses up about 60% of all the power generated, so any improvements can have a dramatic effect on fuel use. Plans were also underway to use the 012's basic concept in an engine outwardly identical to the 004, known as the 004H, which improved specific fuel consumption from the 004B's 1.39 kg/(km/h) to a respectable 1.20 kg/(km/h), a decrease of about 15%.

Apart from the Me 262 and Arado Ar 234, the engine was used to power the experimental Junkers Ju 287, and prototypes of the Horten Ho 229 and Heinkel He 280. There were plans to install it in the Heinkel He 162 as well as the Focke-Wulf Ta 183 and Henschel Hs 132 then under development.

Following World War II, Jumo 004s were built in small numbers by Malesice in Czechoslovakia, designated M-04 to power the Avia S-92, itself a copy of the Me 262. Jumo 004 copies were also built in the Soviet Union as the RD-10 engine, where they powered the Yakovlev Yak-15 as well as many prototype jet fighters.

In France, captured 004s powered the Sud-Ouest SO 6000 Triton and the Arsenal VG-70.

[edit] Variants

Layout: ax=axial flow compressor stages, in=individual combustion chambers, tu=turbine stages.

[edit] Specifications (Jumo 004B)

General characteristics

• Type: Turbojet
• Length: 3,860 mm (152 in)
• Diameter: 810 mm (32 in)
• Dry weight: 719 kg (1,585 lb)

Components

• Compressor: 8-stage axial compressor
• Combustors: 6
• Turbine: Single-stage

Performance

• Thrust: 8.8 kN (1,980 lbf) at 8,700 rpm
• Overall pressure ratio: 3.14:1
• Specific fuel consumption: 1.39 kg/km / h
• Thrust-to-weight ratio: 1.25 (12.2 N/kg)

[edit] Trivia

The Junkers Jumo 004 is perhaps the only aero engine to be featured in popular music, being referenced in the lyrics to the Blue Öyster Cult's "ME 262" from the 1974 album, Secret Treaties.

[edit] See also

• Rolls-Royce Derwent - contemporary British engines
• De Havilland Goblin - contemporary British engines

• List of motors of WW2 Luftwaffe Aircraft
• List of aircraft engines