The Jumo 004 (109-004) Turbojet

The Jumo 004 project was initiated in late 1939 in a project led by Dr Anselm Franz, then in charge of Junkers' turbo- and supercharger development. The Heinkel company had proved the potential of jet propulsion as early as 1937, and the German Air Ministry encouraged other engine manufacturers to initiate their own jet engine developments. The 004 was assigned the RLM designation "109-004"

German turbojet-engine development work had begun in the mid-1930s, with the initial concepts conceived by an engineer named Hans-Joachim Pabst von Ohain, whose efforts paralleled those of Frank Whittle of Britain.

In 1933, while von Ohain was working on his doctorate at the University of Goettingen, he began investigate the gas turbine as a basis for an advanced aircraft engine. Although most of the feedback he received suggested that gas turbines would be too heavy for such a role, he pressed on anyway, developing a demonstrator model of a "turbojet" engine in his garage, with the help of a mechanic named Max Hahn.

Von Ohain managed to impress his professor, R.W. Pohl, with a test run of the model. Pohl was both open-minded and well-connected, and in 1936 he sent von Ohain on to aircraft manufacturer Ernst Heinkel with a letter of recommendation. Von Ohain defended his ideas under grilling by Heinkel engineers, and was put in charge of a design team to develop a practical turbojet engine.

Von Ohain's team had a working bench-test prototype in September 1937, six months after Whittle had reached the same benchmark. Von Ohain's prototype burned hydrogen, which was not a practical fuel, but further work with Max Hahn led to an engine that burned kerosene.

Ernst Heinkel gave the go-ahead to develop a flight-test engine, designated the "HeS-3", which was strapped to an He-118 dive bomber for evaluation. Tests began in May 1939 and continued until the engine burned itself out a few months later. Enough had been learned to build a pure jet-powered experimental aircraft, the "Heinkel He-178", powered by an improved "HeS-3B" engine with 2.94 kN (300 kgp / 835 lbf) thrust. Later in the flight test program, the He-178 would be fitted with a further improved "HeS-6" turbojet with 5.78 kN (590 kgp / 1,300 lbf) thrust.

The He-178 was a simple "flying stovepipe", with straight-through airflow from nose to tail. The aircraft had high-mounted tapered wings and a conventional tail assembly. Although it had fully-retractable "tailsitter" landing gear, the landing gear was bolted into the down position.

The He-178 performed its first test flight on 27 August 1939, a few days before the outbreak of World War II. The flight lasted about five minutes, with the pilot reporting that the aircraft "had no vibration and no torque like a propeller engine. Everything was smooth, and ... felt wonderful." Von Ohain was now well ahead of Whittle, whose efforts were bogged down, first by official indifference and then by national crisis. Whittle would not fly his own experimental jet aircraft, the "Gloster-Whittle G.40", until May 1941.

The Luftwaffe and the German Air Ministry ("ReichsLuftfahrtMinisterium / RLM") were preoccupied with war, and the authorities didn't witness a flight demonstration of the He-178 until November 1939. They were generally unimpressed, since the He-178 was not as fast as the best piston fighters. Heinkel was told: "Your turbojet is not needed. We will win the war on piston engines."

After a total of about a dozen test flights, the He-178 was sent to the national air museum in Berlin, where it was destroyed in a bombing raid in 1943. A second He-178 was planned, but not completed.

Although the RLM seemed indifferent to the He-178, the ministry was nonetheless actively pushing German industry to develop turbojets. In hindsight, it seems that the left and right hands of the RLM were not in agreement, which summarizes most of the Third Reich's attempts to develop advanced weapons.

Hans A. Mauch had become head of rocket development at the RLM in April 1938, and quickly expanded his office's charter to emphasize turbojet development, working with an experimental department under Helmut Schelp in the RLM research branch. By mid-1938, the two men had set up a comprehensive program of jet engine development that was soon sponsoring a range of turbojet and turboprop projects.

The design Dr Franz at Junkers Motoren (Jumo) initiated differed from von Ohain's design by using a new type of compressor, recently developed by the Aerodynamische Versuchsanstalt (AVA - Aerodynamic Research Institute) at Göttingen. This was an axial-flow compressor, which offered greater efficiency and a smaller cross section then the earler designs.

In order to speed development and production of the new design, Dr Franz used a simple combustion area using six "flame cans". This was less efficient then the single annular can, but was simpler to implement. He also collaborated on the development of the engine's turbine with Allgemeine Elektricitäts-Gesellschaft (AEG - General Electric Company) in Berlin. This approach was proved correct when the Jumo 004 entered production and service much earlier then the competing BMW 003 design

Before this, in the fall of 1938, a Messerschmitt design team under Dr. Waldermar Voight had drawn up concepts for a interceptor fighter with twin turbojet engines. The preliminary designs for "Project 1065", as it was designated, went through a iteration or two and finally resulted in a proposal submitted to the RLM in May 1940

Messerschmitt's dream fighter had the turbojets mounted in nacelles under the middle of the wings. The wings were slightly swept to ensure proper center of gravity, and had an unusually thin chord, or ratio of thickness to width, for good high-speed performance. Since the wing's features for high-speed performance compromised low-speed handling, a "slat" was added to the front of the outer wings. The slat was automatically extended to improve handling at low speeds.

The fuselage had a triangular cross section and substantial fuel capacity to feed the thirsty engines. The aircraft was a "taildragger", with fully retractable landing gear. In July 1940, the RLM ordered three prototypes, under the designation "Messerschmitt 262 (Me-262)", to be powered by BMW-003 engines.

Airframe development far outpaced engine development, and so the first prototype, the "Me-262-V1" ("V" standing for "Versuchs / Experimental"), was fitted with a single Jumo-210G piston engine with 530 kW (710 HP) and a two-bladed propeller for preliminary test flights. First flight was on 18 April 1941. The RLM was becoming more interested in the aircraft, ordering five more prototypes in July 1941, to follow the initial order for three.

The Me-262-V1 was finally fitted with a pair of BMW-003 turbojets, each with 5.40 kN (550 kgp / 1,200 lbf) thrust, in November 1941. The Jumo 210G piston engine was retained, which was fortunate, since the turbojet engines were hopelessly unreliable. On 25 March 1942, Messerschmitt test pilot Fritz Wendel took off and suffered immediate failures of both engines. He managed to make a go-round on the piston engine and land, damaging the aircraft but suffering no injury himself.

The BMW 003 engine was abandoned for the Me 262, being replaced by the Junkers Jumo-004 which seemed more promising. The third prototype, the "Me-262-V3", was fitted with two Jumo-004A pre-production engines with 8.24 kN (840 kgp / 1,850 lbf) thrust each. Wendel took the V3 into the air on 18 July 1942 and found the aircraft extremely impressive. Work on the BMW 003 continued at BMW, and by late 1942 it had been made far more powerful and reliable. The improved engine was flight tested under a Junkers Ju 88 in October 1943 and was finally ready for mass production in August 1944.

Apart from the Me 262 and Arado Ar 234, the engine was used to power the experimental Junkers Ju 287 , and prototypes of the Gotha Go 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.

Derived from an article by Greg Goebel