Aircraft Engines - German Turbojets - Part 14
German turbojet engines
Hans von Ohain
The world's first classic turbojet was the German Heinkel He.178. This is a statement that we will not discuss. Success has many fathers, failure is an orphan. For this reason, many laboratories, factories and construction teams in Germany are usurping the palm of priority in this field. There is such a thicket of information that it is difficult to be reliable in it. Therefore, we will focus on a few important facts that seem irrefutable.
It is impossible to talk about German turbojet engines without mentioning the engineer Dr. Hans von Ohain (1911-1998). Hans Joachim Pabist von Ohain was born in Germany. He was a physicist and creator of the first so-called operational turbojet engine. In 1933, he formulated the theory of jet propulsion. Also in 1933, Hans von Ohain wrote his doctoral dissertation at the University of Göttingen on the optical microphone with which it is possible to record sound directly onto film. Siemens bought this patent. Hans von Ohain used the money obtained in this way for his interests, i.e. gas turbines.
Hans von Ohain drove his car to the workshop where he met the mechanic Max Hahn. In 1934, Hans von Ohain offered the mechanic to build a gas turbine together and pay RM 1,000 for the work. The proposal was accepted and the first version of the German engine was built in the garage. The tests were successful, despite the poor thermal resistance of the metals used and the rapid wear of the components.
In 1935, Hans von Ohain obtained another doctorate in physics and aerodynamics from the University of Göttingen and became a junior assistant to professor Robert Pohl. In 1936, Hans von Ohain patented the concepts of a turbojet engine. Thanks to Professor Robert Pohl, Hans von Ohain got in touch with the manufacturer Ernest Heinkel, who became interested in the project. A small laboratory was set up at the Marienehe airport near Rostock. Several changes were made to the design and this is how the Heinkel-Strahltriebwerk 1 engine, abbreviated as HeS 1, was created. Later, this engine was referred to as the Heinkel Jet Engine 1.
The engine was very simple and made mainly of steel plate. It was extremely short because the compressor and turbine were placed close together, back to back. The compressor and turbine were of the centrifugal (radial) type. The combustion chambers are arranged in a circle on the outside. This made the engine very bulky. He worked on hydrogen.
Construction of the engine began in September 1936 and was completed in March 1937. The first launch took place in September 1937. The engine was not suitable for installation in an airplane, but beyond all doubt it was a good basis for building an aircraft propulsion. The designers had problems with the combustion stability and maintaining the optimal speed of the turbine. Often, fuel ignition took place outside the combustion chambers. The flames coming from the outlet nozzle overheated the electric motor that was used to accelerate the turbine. In the course of further work, hydrogen was replaced with gasoline.
The next step in the program was the HeS.3 engine, which was already designed to drive an aircraft. The main design change was to move the compressor and turbine away from each other and to insert the combustion chambers into the space created. The cross-section of the entire engine decreased. The second difference was that the entire engine was significantly enlarged to obtain more thrust to make the engine capable of propelling the aircraft. Over time, the shape of the fuel combustion chambers in the HeS.3b model was changed to shorten the distance between the compressor and the fuel injectors. The HeS.3b engine was compact. Its first launch took place in July 1939. The first HeS.3b engine overheated quickly and burned out. But the second copy was already being completed and it was installed in the Heinkel He 178 airframe. The plane made its first flight on August 27, 1939. The pilot of the Heinkel He 178 was Erich Warstiz. Two prototypes of the aircraft were built. The engine was mounted just behind the center of gravity of the airframe, in the area of the wings.
The He 178 plane flew very badly because of a too weak engine. He was barely lifting himself from the ground. He made turns with a slight tilt, because he was in danger of losing. Anyway, all German turbojet planes from the war period flew very poorly. So let's not be surprised that the interest in the project was minimal. Nevertheless, Heinkel started working on another HeS.6 engine, i.e. an enlarged HeS.3b and HeS.8, with an annular combustion chamber. The HeS.8 engine was to be used in the He 280 fighter. However, the engine development was dragged on.
The initial lack of interest in turbojet engines by the German authorities resulted in a significant reduction in further work by Hans von Ohain, who did not have sufficient support. However, other designers saw the potential of the turbojet and began to develop their own designs, which over time overshadowed the successes of Hans von Ohain. None of the Hans von Ohain engines entered mass production and was not used in service.
Frank Whittle and Hans von Ohain had similar difficult working conditions. They both went against the tide and both met with the distrust of conservative constructors and decision makers. The idea of Frank Whittle was carefully scrutinized by the British Air Ministry and rejected as impossible. Hans von Ohain received similar views when he presented his concepts to the construction team at Heinkel. However, both of them had sufficient persuasion to find a few allies and receive partial help. Frank Whittle went to study at Cambridge at the expense of the ministry, and Hans von Ohain took up the position of an independent designer at Hainkel. Both achieved their first success around 1937, putting into operation the first gas turbines for aircraft propulsion.
In 1947, Hans von Ohain was taken to the US as part of Operation Paperclip, where he began working for the United States Air Force. In 1956, he became director of the Air Force Aeronautical Research Laboratory, and in 1975, scientific head of the Aero Propulsion Laboratory.
The first flight of the He 280 with HeS.8 engines took place on April 2, 1941. On April 5, 1941, the He 280 aircraft was demonstrated to authorities. Everyone was impressed, and only then did orders and funds flow.
However, there were other designers on the market at this point. Junkers with Jumo 004 engine, BMW with BMW 003 engine and HeS.30 with axial compressor (not implemented by Hans von Ohain). The HeS.8 engine never reached mass production maturity and was abandoned in the spring of 1943. German experts say that the main reason for the failure of HeS.8 was simultaneous work on other projects. In 1940, Heinkel was working on ramjet and pulse motors. A separate program has also been launched for the development of an axial compressor. As a result, individual teams fiercely competed with each other, and politics was involved in it all. It was established, inter alia, that the He 280 aircraft will be powered by two engines, either HeS.6 550 kg each, or in the future HeS.8 700 kg each, or a competitive HeS.30 with an axial compressor. The He 280 aircraft was built in 9 prototypes. Various engines were tested on it. During the first flight in September 1940, the first prototype was destroyed. He was unable to break away from the ground.
While the HeS.8 engine offered 700 kg thrust, the new competitor, the Heinkel HeS.30 engine, was developing 860 kg thrust as early as October 1941. Not only that, there was a prospect of increasing the thrust to 1,000 kG. Nevertheless, Heinkel management decided to abandon the development of these engines as the first generation and ordered them to proceed with the program aimed at a 1,300 kg engine thrust. It was about a clear advance of Junkers and BMW. This new engine was never made.
The BMW 003 engine (full RLM designation BMW 109-003) is a turbojet engine produced by BMW AG in Germany during World War II. The BMW 003 and Junkers Jumo 004 engines were the only German turbojet engines to go into production during World War II.
Work on the BMW 003 project began ahead of its rival Jumo 004, but protracted development problems saw the BMW 003 go into production much later. Airplanes were designed to mount different engines.
About 3,500 BMW 003 engines were built in Germany, but very few have ever been installed on aircraft. The BMW engine also laid the foundation for the development of jet aircraft in Japan during and after the war in the CCCP. The BMW 018 was a more modern engine, but only three prototypes were built by the end of the war. This version of the engine was used as the basis for the successful post-war French Snecma Atar engine.
The airplane Messerschmitt Me 262.
The Messerschmitt Me 262 is an important turbojet aircraft that it was used operationally and was built in large numbers.
It is not known why, in 1938, the German aviation ministry placed an order for a turbojet from Messerschmitt. After all, one had to know that there was a laboratory dealing with turbojet engines in the Heinkel concern and the construction of an experimental aircraft was already started, which was tested in August 1939.
The Messerschmitt aircraft was to be powered by two BMW engines. The airframe was marked P.1065, and the entire aircraft Me 262. The airframe was completed at the end of 1940. However, the BMW 003 engines were in their infancy. There is no doubt that major policymakers fought each other. The project was accused of being unrealistic. Funds were blocked. Protests were received. The first Me 262 plane flew on April 18, 1941, and was powered by one conventional 700hp Junkers Jumo 210G engine mounted in the nose of the machine. The first flight with BMW 003 engines took place on March 25, 1942 with a preserved piston engine. And this saved the prototype, because the turbojet engines stopped working right after take-off. The compressor blades have failed. Suspected due to pumping. The third Me 262 prototype was equipped with Junkers Jumo 004 engines, which proved to be more reliable. It was the first plane without an additional piston engine. His flight test took place on July 18, 1942.
Initially, the plane had a classic landing gear with a tail wheel. But then the exhaust fumes from turbojet engines tore the turf and destroy the surface of the ascent area. Therefore, a landing gear with a front wheel was used, which leveled the plane, and at the same time improved the visibility from the flight deck. For various reasons, serial production of the Me 262 aircraft did not start until 1944. Despite its shortcomings and underdevelopment, the Me 262 signaled the arrival of a new era.
The BMW 003 engine powered such planes as Me 262, Heinkel He 162, Arado Ar 234. Work on it started ahead of the competitor Jumo 004, but was completed later due to the problems encountered. Work on the engine began at the end of 1938 at Bramo in Berlin as the P3302 (109-002) project. At the same time, BMW ran its own program 109-003. The Bramo program was more promising, but the company was taken over by the BMW concern, so one program was created, which was eventually designated BMW 003.
In mid-1940, the engine was tested as an auxiliary propulsion on the Messerschmitt Bf 110. The results were disappointing. There was even an intention to quit the program. But during this time, the HeS.3b engine continued to thrive and worked. Probably at that time the BMW 003 engine was completely redesigned. The engine received an axial compressor so that the frontal resistance was as low as possible. During the period 1939-1941, about ten prototypes were built. According to the announcement of the BMW company, the engine gave a thrust of 800 kG, while in fact the max thrust was 500-600 kG, which, however, could not be verified. The stakes were very high, so the lie was used. In early 1942, the engine was redesigned. It has been enlarged so that the compressor passes 30% more air than before. In 1943, a full 800 kg of thrust was obtained. The first satisfactory BMW 003 engine was tested on the Ju-88 in October 1943. In 1944, the BMW 003 engines were mounted on the Arado Ar 234 aircraft. The aircraft did not reach a sensational speed, but reached an altitude of 13,000 m, which was an excellent result. Mass production started at the end of 1944, but for various reasons it was not possible to achieve full production capacity.
BMW 003 engine data: The BMW 003 engine has one shaft. The axial compressor consists of 7 stages. Paddles made of steel. Annular combustion chamber with 16 fuel injectors. 1-stage turbine. Length 3.635 m, diameter 0.69 m, thrust 7.84 kN (800 kG), at 9,500 rpm, weight 620-623 kg. Exhaust gas temperature after the turbine 620 degrees C. Aviation gasoline fuel with an octane number of 87, marked as B4. Fuel consumption 1.48 kg / kp.h (151 kg / kN.h). Thrust to weight ratio 1.29 kp.kg (0.01265 kN / kg).
The plans for the BMW 003 engine were transferred to Japan, where the Ishikawajima Ne-20 version was developed for the Nakajima Kikka aircraft.
Junkers Jumo 004.
The Junkers Jumo 004 engine began to be developed later than the BMW 003 engine. Both engines have very similar designs. The first launch of the Junkers Jumo 004 engine on the ground took place in 1940. The Junkers constructors coped with the difficulties faster and that is why the engine was the first to successfully drive the Messerschmitt Me 262 and Arado Ar 234 aircraft. Later it also powered other structures. The Junkers Jumo 004 engine variants were mass-produced in CCCP and Czechoslovakia.
The Junkers turbojet engine laboratory was established at the beginning of 1940. The team was headed by Dr. Anselm Franz. The program was approved by the Ministry of the People's Republic of China and was designated RLM 109-004. The Ministry gave the prefix 109 to all jet engine designs. Even rocket engines designed for piloted aircraft.
The Jumo 004 engine also received an axial compressor. Its diameter was about 10 cm smaller than that of the BMW 003 engine. To facilitate construction and production, the stator housing in the compressor area consisted of two halves instead of a single cylinder. Anselm Franz was criticized for this solution, but during production he was admitted to be right. Another difference was the use of six flame cans (combustion chambers) instead of the annular combustion chamber. This solution in fact simplified the production, although combustion is less efficient with such a system. During the production of the engine, it turned out to be much simpler than the production of reciprocating engines. One Jumo 004 series engine took 400 man-hours to build, while reciprocating engines required over 1,000 man-hours. The machine park is also poorer. In fact, the engine could be built with tools designed to build car bodies. Of course, the durability and reliability of the Jumo 004 turbojets were far below expectations. But here the problem was the lack of high-temperature metals.
Both the Jumo 004 and BMW 003 engines used an identical starter for starting. The starter is a 10 HP (7.5 kW) 2-cylinder, two-stroke boxer engine by Norbert Riedel. The procedure for starting turbojets was also similar.
The choice of fuel was a problem for the designers. The first Jumo 004 engine, launched in October 1940, ran on diesel fuel. Ultimately, the engine was designed to run on three different fuels: diesel fuel, synthetic gasoline produced from hard coal (J-2), aviation gasoline. J-2 fuel was the best fuel for the engine. Aviation gasoline had a too high combustion temperature, which resulted in faster engine wear. Diesel fuel caused soot build-up on the injectors.
In early 1941, the Jumo 004 engine reached 430 kg (950 lbf), but the ministry demanded a minimum of 600 kg (1,300 lbf). This requirement resulted from the combat weight provided for the Me 262 aircraft.
The constructors had to face the problem of too much vibration in the compressor area. The compressor stator initially made of aluminum was replaced by one made of steel.
The final engine configuration was as follows: an engine almost entirely made of steel. It was also related to the lack of strategic raw materials: nickel, cobalt and molybdenum. Only the turbine blades were made of Cromadur alloy developed by the Krupa plant, containing: 12% chromium, 18% manganese and 70% iron. All engine elements were joined by welding or twisting with bolts and screws. 8-stage axial compressor. Combustion chamber consisting of six flame cans cooled from the outside by air flow. Single stage turbine with hollow blades and cooling air flowing through them. So configured in December 1941, the engine passed a 10-hour test of continuous operation, generating 9.8 kN (2,200 lbf) thrust. The first flight tests were carried out in March 1942 with the Messerschmitt Bf 110. On July 18, 1942, the Me 262 took off into the air with Jumo 004 engines. It was then decided to order 80 engines.
The serial Jumo 004 engine weighed about 800 kg. After the conducted ground tests, the engine received a certificate of durability of 100 hours of operation with a repair period of 50 hours. As it turned out, it was a theory. In 1943 it was confirmed that hardly any engine lasted 20 hours of operation. Usually the turbine blades were damaged. These failures resulted in the suspension of serial production. The constructors looked for the reasons in material defects or faulty welding. It turned out, however, that the cause was the vibration frequency. As a result of the analyzes, it was decided to shorten the turbine blades by 1 mm. As a result of this procedure, the spool speed dropped from 9,000 rpm to 8,700 rpm and the engine thrust dropped from the declared 9.8 kN to 9.2 kN.
Only in 1944, serial production could start at full speed. It is estimated that 5,000 - 8,000 Jumo 004 engines were built. The Germanic ones themselves do not give a reliable number. But what about when the steel from which the engines began to be made deteriorated. At that time, there were already carpet bombing raids on the Pipe Basin and the steelworks often stopped working. The engine had a service life of 10-25 hours and usually not suitable for any overhaul. These 25 hours were achieved on the condition that an experienced pilot who could smoothly operate the gas was at the controls. Too rapid addition of gas caused too much fuel to be supplied before the turbine accelerated. The effect was that some of the fuel was already burning outside the combustion chamber, in the area of the turbine blades, overheating them.
An adjustable nozzle was developed for the Jumo 004 engine. The change in the area of the outlet cross-section was realized by a central cone, which had the shape of an onion. It was moved axially over a length of about 0.40 m by an electric mechanism.
After the Second World War, the Jumo 004 engine was produced in Czechoslovakia as the Avia M-04 and in the CCCP as the Tumański RD-10.
Jumo 004B basic version data: length 3.86 m, diameter 0.81 m, weight 720 kg, 8-stage axial compressor, 6-flame cans, single turbine, adjustable discharge nozzle. Maximum thrust of 8.8 kN. Compressor 3.14: 1 compression. Fuel consumption 1.39 N / (N hr). Thrust to weight ratio 1.25 (12.2 N / kg).
Written by Karol Placha Hetman