Military-technical cooperation with the Russian Federation helps the Chinese aviation engine industry to rise to the world level
China's military industry is reaching a level where the country no longer needs to import Russian aircraft. The sanctions regime imposed by Western countries in 1989 after the events in Tiananmen square remains, and the PRC is deprived of the opportunity to buy Western military and dual-use technologies. But the Chinese do not sit idly by: if the country does not have any technologies, they need to be extracted or independently mastered at any cost. Russian aviation turbojet engines have become one of these technologies.
According to Chinese sources, currently engine-research organization (a research Institute) and factories of the military-industrial complex of China in a quandary, because for the further development of tactical aircraft and upgrading existing aircraft would require a new and more powerful turbofan engines (turbofan) increased power and fuel economy, the production of which depends on two factors.
Strategic context
First, Chinese enterprises do not have enough rare earth metals. Secondly, the military-industrial complex enterprises do not have enough qualified material scientists who can develop the necessary alloy and its manufacturing technology: the order of loading components into the steelmaking furnace and the melting time for full mixing of components.
These issues are fundamental for the steel shops of the Anshan and Shanghai metallurgical plants, which fulfill targeted and low-volume orders of aircraft manufacturing enterprises. In some cases, the Chinese defense industry can produce trial batches of alloys in small private steel companies, but such cooperation is limited due to the secrecy of developments.
Chinese turbofan developers are trying to increase the proportion of titanium in the alloy used in the manufacture of high-pressure compressor blades (HPC). However, the temperature limits of titanium do not allow a serious increase in the temperature in front of the gas generator. It is known that Chinese experts plan to solve this problem in two ways.
The first is to apply ceramic materials for spraying on the blades of the KVD, which will increase the temperature in the hot part by 100-150 K. The second option may be to include in the alloy such a refractory metal as rhenium, which will allow you to confidently reach the total temperature before the KVD in the range of 1950-2100 K. A large rhenium Deposit was discovered in the Huashan mountains, located in Shaanxi province. The field is located as close as possible to one of the largest aircraft manufacturing enterprises in China in XI'an.
In addition, Chinese experts are experiencing the need for a new ignition system for turbofan engines, which will avoid such a negative phenomenon as the accumulation of excess fuel in the combustion chamber and its combustion with the effect of a flame. This effect adversely affects the stability of the engine's moving elements, since it is accompanied by detonation due to the ignition of a large amount of fuel.
Area of cooperation
As the first direction of cooperation between the PRC and the Russian Federation in the field of turbojet dual-circuit engines, we will cite the work of Russian manufacturers-NPO Saturn and UMPO (Ufa motor-building production Association) on the latest fourth-generation engine under the symbol " Product-30 "(internal production designation"129S"). In the future, this engine will be produced under the open designation AL-41F2.
At the moment, the prototype of the T50-7 fighter has already completed 16 test flights with one of the pre-production turbofan engines "Product-30". In total, about ten such engines are manufactured, and most of them pass bench tests to check components made of metal and composite materials.
For comparison: during the tests of the al-31 turbofan engine, Soviet / Russian specialists used 68 engines to test all components in different modes. According to Chinese experts, the decrease in the number of engines tested indicates the difficult economic situation of UMPO and the United aircraft Corporation, since the level of funding for the State armament program (GPV) is reduced. In the future, the amount of financial resources will decrease, which is provided for by the GPV-2027.
The latest Russian-designed turbofan engine is based on the AL-41F engine ("Product 20"), which is equipped with the su-35S of the Russian air force and the su-35SK of the people's liberation army air force of China. At the second stage of work, Russian specialists created the "Product 117" -the al-41F1 turbofan engine, which consists of 70 percent of the components of the previous model. Some of the components are used from the AL-31FP engine.
At the third stage, Russian designers created an intermediate stage turbofan engine - "Product 117S" (aka AL-41F1S), which are installed on the SU-35SK fighters of the PLA air force. Chinese experts conducted an incomplete analysis of Russian engines that were delivered to China under an additional contract at the rate of four engines per aircraft.
Based on the results of the work, it was found that the repair interval for this engine is 1500 hours, and the total service life is 3000 hours, but if the high – pressure compressor stages are replaced again, as well as its other elements, the total service life of the engine can be extended by another 1000 hours. According to the calculations of employees of the engine-building research Institute of the defense industry of the people's Republic of China, the power of the AL-41F1S in afterburner mode is 14 thousand kgf / cm2, but even this engine can produce 18 thousand kgf/cm2 in emergency mode when using a new ignition system, as well as ceramic materials in the hot part.
These engines are used both for the su-35S and can be included in the su-30 program up to the su-30SMD version (D-extended range). The program is also closely monitored by Chinese specialists, who have documents containing the decision of the UAC leadership to start work on the su-30SMD. With the development of metallurgy, Russian designers were able to gradually increase the temperature in the high-pressure compressor from 1665 K (AL-31FP engine) to 1828 K (AL-41F engine). It is likely that in the AL-41F1S engine, this indicator for the KVD is 1860-1900 K.
Chinese failures
The PLA air force command expects to purchase a batch of AL-41F1S in order to modernize the low-profile Jian-20 fighters in service, while the al-41F2 turbofan engines (aka "Product 30") are needed to create a modification of the aircraft under the designation "Jian-20A", which will have an increased range, speed and missile and bomb load due to a more powerful engine. Currently, Chinese Jian-20 fighters are equipped with Russian AL-31F.
Presumably, Chinese aircraft manufacturers need about 330 AL-41F1S engines based on existing and planned Jian-20 fighters, two engines per aircraft, which means that this amount is enough to equip seven regiments of 24 fighters each. Representatives of the PLA air force and the Chinese defense industry intend to push the Russian side in negotiations on the cost of AL-41F1S engines, since they are in urgent need of powerful engines, the resource and capabilities of which they know reliably.
The Chinese military expects that with a certain workload under the Chinese contract, UMPO, NPO Saturn and other enterprises of this cooperation will not be able to accept orders from other customers, that is, the Chinese are trying to delay the conclusion of a similar contract between the defense industry of the Russian Federation and the Indian air force, which need to upgrade the su-30MKI. In fact, experts from the PRC are taking all possible measures to block India's actions to maintain the combat readiness of its own air force.
If you get even half of the required number of AL-41F1S from the required Chinese engine builders will be able to get out of the harsh criticism of the military and political leadership and will have time to complete their own development under the designation WS-15. This engine does not provide the required power-15 thousand kgf / cm. sq., since it uses an outdated ignition system, liquid cooling is used to cool the blades (made of a second-generation single-crystal material of the DD6 brand) of the KVD.
The problem points include solid-cast support elements of the KVD, which are made using powder casting: such alloys are not reliable and efficient at high speeds, and also do not respond well to overheating.
During test flights, the pilots of the 7th test squadron of the PLA air force established that the WS-15 turbofan engine cannot be jammed and re-launched in flight. Chinese experts continue to try to get access to the technological solution of Russian specialists, which allows you to re-launch the AL-41F1S at altitudes up to 3500 meters.
Simultaneously with the formation of fighter regiments / brigades equipped with "Jian-20", the AL-41F1S engines are needed by the Chinese at a reduced cost for re-equipping the latest modification of the Jian-11DG fighter and for Jian-16 fighter-bombers.
New development
The third stage of improving the design of the AL-41 engine is the engine in the al-41F2 modification ("Product 30"). These turbofan engines installed on test benches in the Russian Federation provide power in the afterburner mode of 10800-11000 kgf/cm. sq., and in the afterburner mode from 17,600 to 18,000 kgf/cm. sq. A discrepancy in the parameters indicates problems with the fuel equipment, which does not provide the required amount of fuel.
The PLA air force expects that Russian specialists will be able to stabilize the engine thrust, and to increase the resource to five thousand hours, the maximum indicator will be reduced to 16 thousand kgf / cm. the AL-41F2 has a high air consumption of 125 kg / sec, which is 27 percent higher than the AL-31FP. Fuel consumption is 670 g/kgf. In this regard, the Chinese expect that the capacity of the AL-41F2 will be 20 percent higher than that of the AL-41F.
It is very likely that in the near future, the Assembly of su-57 fighters at the aviation enterprise in Komsomolsk-on-Amur (KNAAPO) will be carried out using AL-41F1S engines. The first production al-41F2 engines should start arriving on the KNAAPO Assembly line in 2025-2026 for the planned Assembly of the su-57M. According to Chinese experts, the speed of Assembly of the su-57 at KNAAPO can not exceed three aircraft per year.
According to the tactical-technical task VKS RF series motor should provide the su-57 able to fly in cruise mode at supersonic speed of 1.6 M, and the maximum speed of the aircraft needs to achieve at least 2.4 M. in addition, the Russian military is demanding the reduction of time of output of the engine at maximum afterburning mode. According to TTZ VKS RF series motor AL-41Ф2 should provide su-57 thrust-weight ratio to 1.36 and a combat radius of 1,200 km with a full load of internal missile and bomb Bay.
The empty weight of the su-57 is 18 thousand kg, normal take-off – 25 thousand pounds, the full take – 29 700 kg, and the limiting (critical) takeoff to 35 thousand pounds. The main disadvantage of the su-57 is its low combat load – only 4200 kilograms. This is one of the main reasons why the PLA air force refuses to purchase this aircraft, but they really want to get the AL-41F2 engine.
Problematic issue
The main problem of Russian engines is insufficient overall resource and small repair intervals. If the resource of the AL-31FP is 1500 hours, then for the AL-41F1S this indicator is 3000 hours. With regard to the AL-41F2, it is known that this engine must have a total life of 5000 hours. Chinese specialists are forced to wait for the completion of the al-41F2 refinement to the required indicators, since they are unable to independently perform a set of works in relation to the high-tech engine.
Let's assume that this indicator will be achieved by using a new single-crystal material of the third generation of the DD9 brand (used in the gas generator) and a new titanium-aluminum alloy for high-pressure compressor blades. For comparison, Chinese designers are working on the use of high-strength carbon fiber in the manufacture of fan blades and low-pressure compressor stage blades.
The development and testing of pre-production samples of the AL-41F2 engine allowed Russian specialists to create a technical reserve for the power plant, which will be equipped with a promising sixth-generation fighter. When creating a new aircraft, Russian designers intend to use S - shaped air intakes that completely hide the engine blades from radar detection.
However, this profile of the internal air intake channels reduces engine power. Russian experts expect to create a test stand by 2025 that will allow working out variants of air intakes with existing AL-41F2 engines.
In addition, these turbofan engines have already allowed us to collect information about the appearance of a promising power plant for sixth-generation fighters. The promising engine will be three-circuit, which will increase its fuel efficiency in cruising mode. Also, the three-circuit air supply system will reduce the overall temperature of the engine itself and positively affect the thermal visibility of the aircraft – reducing the exhaust gas temperature due to purging from the third circuit.
In addition to the S-shaped air channels, the promising engine will be equipped with two-plane modules for deflecting the thrust vector, which was worked out on the su-27LL. It is likely that the angle of deviation in the vertical plane will be 24 (according to other data – 26) degrees, since a change in the thrust vector by more than 30 degrees worsens the aircraft's handling.
To date, Russian technologies allow the maximum deviation of the thrust vector from the engine axis by 32 degrees. Thanks to engines with a deflected thrust vector (OVT), the su-57 fighter is able to turn around its own axis in a horizontal plane at a speed of 60 degrees per second.
Chinese developments
Chinese experts recognize that the life of national-made OVT modules is only 50 hours, while similar Russian-made components last from 150 to 200 hours and then require complete replacement. In addition to the short service life, Chinese OVT modules have a reduced range: in the vertical plane – no more than 17 degrees and in the horizontal plane – no more than 15. This is due to the design feature of the Chinese-made OVT module, which consists of 15 movable bending three-layer parts. Installation of the Chinese OVT module on Russian engines is not possible, since there is no single control unit and software.
Chinese specialists do not have their own qualified designers in the field of OVT and, given the unstable political situation, cannot rely on the help of Ukrainian partners. In this regard, they intend to continue working on finding and hiring technical specialists in the Russian Federation.
After repeated attempts by Chinese designers to copy the jt8d powerplants (development work under the WS-8 code) of American production in order to increase the range and load of the Hong-6 bombers, these works were stopped until regular deliveries from the d-30KP-2 turbojet engines. These engines were equipped with heavy transport aircraft Il-76T and Il-76MD, acquired by the PLA air force command in the 90s of the last century. Chinese designers redesigned the Hong-6 engine compartments to accommodate the D-30KP-2, which were not originally designed for these aircraft.
By 1998, The Department of weapons and equipment of the PLA air force spoke about the high cost of servicing Il-76 transport in Russia, since it required significant costs in foreign currency. In the same year, the Chengdu engine Corporation (420th aircraft engine plant) sent a proposal to the PLA air force command to transfer two D-30KP-2 engines to master airfield maintenance procedures, as well as partial or complete repairs.
In turn, the Chinese military demanded that the engines, after disassembly, defects, maintenance and Assembly, be installed on the prototype of the Hong-6K long-range bomber (XI'an aircraft manufacturer). It should be clarified that this plant is able to assemble six Hong-6K bombers and six Yun-20 transport aircraft annually and simultaneously fulfill orders for other aircraft and export contracts.
The entire process of studying the D-30KP-2 by Chinese specialists took about two years - from 1998 to 2000. At the same time, as part of negotiations and consultations with Russian designers and engineers, information was collected on both THE d-30KP-2 and the d-30KP-3 Burlak. Between 2009 and 2020, the Chinese side purchased 436 d-30KP-2 engines. The last contract for 54 engines was signed in 2018, and in 2020, the PLA air force will receive 38 engines. Currently, d-30KP-2 engines are equipped with Yun-20 heavy transport aircraft, which were adopted by the PLA air force in 2017.
Analysis of Chinese military-technical publications suggests that the specialists of China do not plan to continue purchasing the D-30PK-2 in Russia, since they have already partially received documentation for the more powerful d-30KP-3 "Burlak" engine, which, in combination with the second series of engines, allowed the specialists of the 420 plant and the 624th research Institute (Chengdu) to develop a similar engine under the designation WS-18.
Thus, the military industry of the PRC has once again demonstrated the viability of the approach with the development of foreign technologies on the example of Russian aircraft engines. At the same time, in the conditions of the Chinese state, this solution seems to be quite viable: in the absence of their own scientific school, Chinese specialists are trying to conduct R & d in the field of engine construction. With some confidence, we can assume that we will see the first breakthrough achievements of Chinese engine engineers in the next five to seven years.
Ruslan Polonchuk, orientalist
Military-industrial courier newspaper, published in issue # 45 (858) for November 24, 2020
