Aviation of World War II
Creation of the TV-2 (NK-12) Turboprop Engine
D.A. Sobolev, D.B. Khazanov
On 3 November 1946 German engine specialists came to Experimental Plant No. 2 located in the settlement of Upravlencheskiy on the Volga River, 30 kilometers from Kuybyshev and 6 kilometers from the Krasnaya Glinka railroad station. The settlement appeared in the late 1930s during construction of the Kuybyshev Hydroelectric Node and consisted of houses for workers and hydro-logical laboratories. During the war, the Kirov 145th Machine-Building Plant evacuated from Moscow occupied the premises.
By the time the Germans arrived at Upravlencheskiy, extant buildings had been repaired and newT industrial blocks and houses erected. The reconstructed plant's production area amounted to 35 acres and included a designer's block, mechanical workshops, laboratories, and test station (built in 1948-1949).
Like the plant at Podberez'ye, Experimental Plant No. 2 had mostly captured German equipment. More than 1000 railroad cars loaded with machine tools, laboratory installations, and other equipment had arrived at the plant from Dessau, Halle, and other German cities.
The number of employees working in 1947 totaled about 2500, including 662 Germans. In addition to A. Scheibe and K. Prestel, the leading German engine specialists there included Dr. Scheinost, who headed the strength and fuel section, Dr. Vogts, Dr. Schulze, and Dr. Cordes.
In early January 1947, Austrian Ferdinand Brandner, former technical director of the Junkers engine production plant in Dessau, joined the "foreign specialists". In May 1945 he agreed to collaborate with the Soviet authorities and passed to them all the technical documentation in his possession. He then was brought to Moscow for consultations on engine production. Brandner hoped that the Soviets, having "pumped" all the information out of him, would permit him to go back to Vienna where his family had moved from Germany. But instead, the Ministry of Internal Affairs sent him to a concentration camp near Moscow. In the spring of 1946, when the government instructed the MVD to search for skilled workers among prisoners so they could work in industry, Brandner was taken from the camp and sent to Aircraft Plant No. 26 in Ufa. At that time, the plant headed by V. Ya. Klimov was beginning series production of Jumo 004 (RD-10) jet engines and Brandnefs experience stood him in very good stead. In late 1946 Klimov was appointed chief designer in Leningrad and Brandner was sent to Experimental Plant No. 2, where he worked in OKB-2, which had been formed from Junkers engine specialists. Later, Brandner wrote about his life in Russia in his autobiography called "Life Between Fronts".
When the plant was being organized the supposition was that the Germans in the USSR would continue the work they had initiated in Germany—creation of augmented series-produced German Jumo 004 and BMW 003 turbojet engines and new powerful Jumo 012 and BMW 018 jet engines. However, in late 1946, a new task appeared: development of turboprop engines. Deputy Minister of the Aviation Industry M. M. Lukin wrote the following to Experimental Plant No. 2 Director N. M. Olekhnovich on 6 December 1946:
Research has been done in TsAGI to define the field of rational use of turboprop engines on high-speed bombers.
According to this research work, the field of rational use of turboprop engines is defined as the speed range from 600 to 900 km/h.
Their use on bombers with maximum speeds of about 750-800 km/h, depending on aircraft weight, is the most advantageous. This advantage expresses itself in a flight range increase of 2000-2500 km, which is 80-100 percent of the entire maximum flight range of the same bombers fitted with piston or turbojet engines.
It would be most advisable to develop a turboprop engine delivering about 4000-4500hp at altitude H=8000 m at a speed of 800 km/h.
I suggest that chief designers Messrs Scheibe and Prestel be assigned the urgent task to design and build a propeller unit for Jumo 012 and BMW 018 engines in 1947".
After consultations with the German specialists, the task was defined more precisely An enactment on experimental engine manufacture the USSR Council of Ministers approved 11 March 1947 tasked Experimental Plant No. 2, as follows:
OKB-1 (chief designer Scheibe) designs and builds: a) 5000hp "022" turboprop engine; b) 2000 kg "032" turbojet with a compressor driven by piston engine.
OKB-2 (chief designer Prestel) designs and builds: a) 6800hp "028" turboprop engine; b) completes the development and hands over for testing the 1050 kg "003C" turbojet engine.
Efforts on the "003C" must be finished by August 1947; other engines were to be presented for testing in mid-1948. The task regarding an augmented version of the Jumo 004 was transferred to Plant No. 26.
In 1947 the group of former BMW employees headed by Karl Prestel was mainly engaged in developing the 003C engine because of the August deadline. The lack of the super alloys used in Germany to make turbine blades was the main obstacle. With the switch from German Tinidur to the domestic EI-403 alloy, engine operating time decreased. The turbojet operating in conventional non-augmented mode could undergo 100 hours of testing but, with a thrust of 1050 kg, operating time did not exceed 25 hours thanks to turbine blade malfunctions. In general this engine, low-pow- ered for 1947. was already of little interest and the theme was transferred to Engine Production Plant No. 16 in Kazan' where BMW 003 (RD-10) engines were being manufactured. Thanks to an improved combustion chamber, turbine, and tail pipe, engine operating time was increased to 50 hours. It was designated RD-21 and was in series production for installation on MiG-9 jet fighters.
Work on the ''032" turbojet with an auxiliary compressor that specialists in the A Scheibe OKB developed was also halted in late 1947. Calculations showed that this type of power plant promised no advantages over the conventional turbojet engine.
Work on the Jumo 012 that was to become a prototype for a future turboprop engine continued in a most energetic way. I would remind you that, by the autumn of 1946, two of these turbojets had been built in Dessau. In the USSR they were subjected to refinement in order to increase their operating time. Thus, at Brandner` s suggestion, a new combustion chamber was made. This was a combination of the BMW annular combustion chamber and the separate combustion chambers characteristic of the Jumo. To reduce the intensity of internal processes, the rate of compression was lowered from 6 to 4.5. Much effort was expended to observe the turbine blade-mounting angle since a violation of this parameter caused a breakdown of flow; vibrations, and other unpleasant phenomena. But, many difficult questions such as nozzle thermal stratification, blade flow phenomena, reasons for sympathetic oscillation, and so on could not be solved without the use of precision instrumentation, which the plant lacked.
Finally, in late 1947, the preliminary studies were completed and an engine designated "012B" went into production. During the summer of 1948, five prototypes were ready and Dr. Vogts was made responsible for their testing. Despite the many changes in the engine design made to prolong the operating time, one problem after another arose. This is from a Ministry of the Aviation Industry report on the prototype engines (1948): "In June No. 5 underwent an endurance test run without takeoff. A compressor rear bearing broke down in the 28th hour. After the bearing and other parts were replaced, the engine ran another 25 hours in July. During this test, cracks were found in turbine blades and compressor stator blades. In the latter half of July, this engine underwent a test in the takeoff mode but, due to defects found, it was removed from the bench".
By late 1948 after a new series of refinements, the "012B" underwent a 100-hour State Test. Success was close, but a turbine blade broke in the 94th hour of engine operation.
In 1948 under V. Ya. Klimov's supervision, the USSR assimilated production of the British Nene turbojet engine, which began to be produced under the designation RD-45. It was much more compact than the German "012B" while retaining practically the same thrust. However, the key was that its weight was less by a factor of 1.5. This predetermined the decision to cease work on the "012B" turbojet.
In parallel with the turbojet testing, in accordance with a Ministry of the Aviation Industry assignment, plant OKB employees were tasked with designing the "022" and "028" turboprop power plants. By late 1947, a theoretical analysis was completed and working drawings began to be released simultaneously with the manufacture of production tooling. However, the work was hampered by a shortage of test benches and other equipment. Therefore, the decision was made in 1948 to combine the OKBs and concentrate efforts on the manufacture of one engine-the "022".
"It should be stated that the presence of two OKBs headed by German specialists and with a complement mainly of German specialists who still have not overcome the elements of bourgeois competition did not ensure that the experience of one OKB was used by the other. Thus, this reason also had an influence on the decision to unite OKB-1 and OKB-2," plant director N. M. Olekhnovich wrote in his 1948 report.
A. Scheibe became the chief designer of the combined OKB, J. Vogts was appointed head of the preliminary design group. F. Brandner headed the design group, and K. Prestel was responsible for testing.
By this time, young Soviet engineers who had just graduated from aviation higher educational institutes joined the ranks of the German specialists. Thus, the entire graduating class of the Engine Department at the Kuybyshev Aviation Institute was sent to Plant No. 2 in 1947.
F. Brandner remembered: "The Russian engineers we had to deal with were inquisitive and industrious. However, at that they were very fond of endless political discussions. As a rule, the young engineers had narrow special education. They were excellently trained theoretically, but completely lacked any practical experience".
The Germans were promised that they would be free to go home after successful turboprop tests. It was a huge incentive for the concerted work of the entire German team.
As has been pointed out, the "022" turboprop engine was created from the Jumo 012 turbojet. This design was conceived initially at the Junkers firm back in 1944 but it had not been realized. Now the Germans had at their disposal a more or less developed "012" engine and it provided some hope. However, many things had to be redone. In comparison with the prototype the "022" had a three-stage turbine and other significant design differences. Also, the propeller, reduction gear, and speed governor had to be designed. The TS-1 starter, a small gas turbine developing 60hp shaft power, was designed to start the engine.
Much attention was paid to increasing engine efficiency since the specifications required that the propellant consumption rate could not exceed 0.32 kg/ehp-hour. For this, compressor blade-tip clearance was reduced to the minimum and the engine air intake diffuser was very carefully shaped. Bypass valves were installed beyond the fifth stage to avoid surging. Theoretical and experimental work was done on the control system (propeller-throttle).
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In mid-1948 the design of the engine was completed and three prototypes ordered for production. A new 6000hp brake test bed was erected at the plant. In 1949 at the height of the work on the "022'' engine, a new director came to Plant No. 2—N. D. Kuznetsov. He already had experience in working with German jet engines: in 1946 along with Klimov and Brandner, he assimilated production of the Jumo 004 in Ufa. Also, he went to Germany to become familiar with German jet technology. Being an intelligent and sociable man, Kuznetsov immediately was liked by the Germans, as Brandner reflected in his memoirs.
In 1950, the engine, given the Russian designation TV-2 ("Turboprop Engine-2") in 1951, was placed in a test stand. After plant tests, it successfully underwent the 100-hour State Test and was admitted to series production. Its maximum equivalent power exceeded 5000hp (shaft power 4663 kg, plus jet thrust 469 kg). "Engine TV-022 No. 14 in its design and operational (under test bed conditions) data conforms to the general tactical and technical specifications of the Soviet Air Forces," according to the report on the State Test. When the testing ended, all German specialists received cash bonuses.
In 1951 two TV-2 engines underwent flight-testing on a Tu-4 aircraft at the Flight Research Institute. They were mounted in place of the bombers outboard piston engines. The airplane made 27 flights with the test engines with a flying time exceeding 70 hours. On 8 October an accident occurred due to a fire in the starboard engine caused by fuel entering the engine nacelle when the engine was started in flight.
Later, the TV-2 was upgraded at P. A. Solov`yev`s OKB and its power increased to 7650 ehp (TV-2M). Counter-rotating propellers were used instead of the conventional four-bladed props. In the mid-1950s some Soviet heavy aircraft such as the first An-8s and Tu-91s were fitted with this engine. This engine became the foundation for creation of the first Soviet helicopter turboprop engine, the TV-2VM, in the mid-1950s.
Let me remind you that a promise was made to allow the Germans to return to their homeland upon completion of the turboprop engine project. In actuality, a group of German specialists and their families received permission to leave the USSR following the successful TX-2 tests. But. far from all were released. In 1950, 241 German engine specialists (610 persons, including their family members) departed Upravlencheskiy for their homeland but several hundred engineers and workers from Germany remained at the plant. They were assigned a new task—to build a turboprop engine of unprecedented power, 12,000hp. Such engines of gigantic power were required for the new A. N. Tupolev-designed Tu-95 strategic bomber.
The simplest way to provide the characteristics the new power plant required was to combine two TV-2 engines with a single reduction gear power transmission. By the way, Germany had a similar experience. In 1939 Heinkel built the He 177 heavy bomber with four paired Daimler Benz engines. True, this experience was not a success because the power plant overheated and a strong vibration arose. But the Experimental Plant No. 2 German specialists either did not know about that, or maybe just preferred to keep silent. All hoped that the long awaited return home would occur after the task was fulfilled, and they tried to finish it as soon as possible. The work began after this idea was coordinated with A. N. Tupolev as a temporary measure making it possible to speed up the testing of the bomber.
Prior to building the "paired" engine it was necessary to augment the existing TV-2. This was achieved through the use of the new temperature-resistant EI-481 super alloy in the turbine structure that allowed an increase in the combustion temperature. Simultaneously use of high-pressure compressor stages with a small insert ratio increased the airflow through the engine. During 1951 bench tests, the TV-2F engine delivered 6250 ehp.
That same year 1951, two paired prototypes designated 2TV-2F were assembled. The engines were placed side by side; one was positioned a little bit behind the other. Their turbine power was transmitted to a single epicyclical gearbox with 0.094 reduction ratio. It rotated two coaxial propellers 5.8 meters in diameter. Power plant control was carried out through a single throttle quadrant connected with each engine.
After some refinement in September 1952, 2TV-2F No 13 underwent the 100-hour plant bench testing. Then, without awaiting the results of state testing, the engines were installed on an aircraft. On 12 November 1952, a Tu-95 fitted with four 2TV-2F engines took to the air for the first time.
Meanwhile, the official bench tests conducted in January and April 1953 showed that the fatigue strength of the reduction gear was insufficient. "2TV-2F engine No. 14 did not pass the 100-hour State Test because a reduction shaft right gear tooth failed and 10 bolts on the load-carrying tube middle flange were broken after 50 hours of operation in the assigned mode...", a January test report stated. "2TV-2F engine No. 15 failed the 100-hour State Test because of spalling of the working surfaces of the right reduction gear drive tooth, destruction of the cover of the right drive shaft, and damage to the hydraulic drive oil seal in the propeller control system after 21 hours of operation in the assigned mode...", this from an April test report.
This is hard to explain from the standpoint of common sense but, despite the fact that State Test conclusions about insufficient engine reduction drive gear strength were repeated twice, Tu-95 test flights continued. What had to happen did happen on 11 May 1953 when, due to a breakdown of the reduction gear in flight, the Tu-95 caught fire, lost control, and crashed. Aircraft captain test pilot A D. Perelet and three crewmembers were killed.
It had become clear already during the first ground tests of the paired TV-2s that a new reliable engine had to be created. Both German and Soviet engineers took part in its design, which began in 1951. A new giant test bench, special braking propeller, and testing devices for the reduction gear and pitch control mechanism were made.
The number of turbine stages in the new engine, with an estimated 12,000hp, was increased to five. Thanks to the new heat-resistant Nimonic alloy, compressor pressure and gas temperature were increased as well. To enhance engine efficiency, much research work was done to reduce losses in blade mechanisms: tighteners minimizing the blade-tip clearance were used and hollow cooled blades of an original design made. A new reduction gear was manufactured and questions concerning the coordination of a turboprop with counter-rotating propellers were solved. Engineer Bockermann was engaged in designing the planetary reduction gear together with Russian specialists and another German engineer named Enderlein worked on the propeller.
More than 100 stand tests of separate systems and units —combustion chambers, reduction gears, collective pitch governors, propeller blades and so on—preceded assembly of the turboprop engine.
These measures resulted in the required power, high reliability and good fuel efficiency of the engine. It proved much more efficient in respect to specific fuel flow than its TV-2 predecessor.
In early 1953, the engine assembly was finished. It was designated TV-12 and later redesignated the NK-12 to reflect the first letters in the name of the plant director.
The bench tests of the TV-12 went well. The engine demonstrated the required power and long operating time. Up until now, there is no engine in the world that matched it in power and a number of other characteristics.
Creation of the TV-2 (NK-12) engine was the final work in which the German specialists took part. In late 1953, the last Germans left the plant. Final tests were conducted and improvements made by a Soviet team headed by N. K. Kuznetsov. The NK-12 and its modifications were successfully used on Tu-95, Tu-114, and An-22 aircraft.