The PLA Air Force wants to load Russian factories with orders to get ahead of India
The sanctions regime imposed by Western countries in 1989 after the Tiananmen events persists, and China is deprived of the opportunity to buy Western military and dual-use technologies. Of course, the Chinese do not sit idly by: if there are no technologies in the country, they need to be extracted and mastered at any cost. Russian aviation turbojet engines have become one of such technologies.
According to Chinese sources, engine-building research organizations and factories of the Defense industry of the People's Republic of China are in a difficult situation. For the development of operational and tactical aviation, new turbojet twin-circuit engines (turbojet engines) of increased power and efficiency are needed, the production of which depends on two factors. Firstly, Chinese enterprises lack rare earth metals. Secondly, there are no qualified materials scientists capable of developing the necessary alloy.
This issue is of fundamental importance for the steel workshops of the Anshan and Shanghai Metallurgical Plants that fulfill targeted low-volume orders of aircraft manufacturing enterprises. Small private companies can also produce trial batches of alloys, but such cooperation is limited due to the secrecy of developments.
Chinese turbofan developers are trying to increase the proportion of titanium in the composition of the alloy for high-pressure compressor blades (HPC). But the temperature capabilities of titanium do not allow to seriously increase the temperature in front of the gas generator. This problem is planned to be solved in two ways.
Firstly, use ceramic materials for spraying on the blades of the KVD, which will increase the temperature in the hot part by 100–150K. Secondly, it is possible to include such a refractory metal as rhenium in the alloy, which will allow to reach the temperature before the KVD in the range of 1950-2100 K. A large deposit of rhenium has been discovered in the Huashan Mountains in Shaanxi Province near an aircraft manufacturing plant in the city of Xi'an.
In addition, Chinese specialists need a new ignition system for turbofan engines, which will avoid the accumulation of excess fuel in the combustion chamber and its combustion with a flame effect. This effect adversely affects the stability of the moving elements of the engine, since it is accompanied by fuel detonation.
AREAS OF COOPERATION
As the first direction of cooperation between China and the Russian Federation in the field of turbofan engines, we will cite the work of NPO Saturn and UMPO (Ufa Engine-Building Production Association) on the latest 4th generation engine under the designation "Product-30". In the future, this engine will be produced under the open designation Al-41F2. The prototype of the T50–7 fighter has already completed 16 test flights with one of the pre-production turbofan "Product-30". In total, about 10 units of such motors have been manufactured, most of them are undergoing bench tests to check components made of metal and composite materials. For comparison, during the tests of the Al-31 turbofan engine, 68 engines were used to test all components in different modes. According to Chinese experts, the decrease in the number of engines tested indicates the economic difficulties of UMPO and the United Aircraft Corporation (UAC).
The latest Russian-designed turbofan engine is based on the Al-41F engine ("Product 20"), which are equipped with Su-35S fighters of the Russian Aerospace Forces and Su-35SK of the PLA Air Force. At the second stage of the work, a "Product 117" was created – the Al-41F1 turbofan engine, which consists of 70% of the components of the previous model. Some of the components are used from the Al-31FP engine. At the third stage, an intermediate stage turbofan engine was created – "Product 117S" (Al-41F1S). They are installed on the Su-35SK fighters of the PLA Air Force.
Chinese experts conducted an incomplete analysis of the Russian engines received in China under an additional contract. It is established that the repair interval for this engine is 1500 hours, and the total resource is 3 thousand hours, but with the repeated replacement of the KVD stages and other elements, the service life can be extended by another 1000 hours. According to the calculations of employees of Chinese engine-building research institutes, the power of the Al-41F1S in afterburner mode is 14,000 kgf / cm2, but this engine is capable of delivering 18,000 kgf/cm2 in emergency mode with a new ignition system and the use of ceramic materials in the hot part.These engines are used for the Su-35S and can be included in the program for the Su-30SMD version (extended flight range). This program is also under the close supervision of the Chinese, who have documents containing the decision of the UAC leadership to start work on the Su-30SMD. Russian designers managed to increase the temperature in the KVD from 1665 K (Al-31FP engine) to 1828 K (Al-41F engine). Probably, in the Al-41F1C engines, this indicator is 1860-1900 K.
FAILURES OF THE CHINESE
The PLA Air Force Command expects to purchase a batch of Al-41F1S to modernize the unobtrusive Jian-20 fighters. And the Al-41F2 turbofan engine ("Product 30") is necessary to create a modification of the Jian-20A with an increased range, speed and missile and bomb load. Currently, the Jian-20 fighters are equipped with Russian Al-31F.
Presumably, the Chinese need about 330 Al-41F1S engines based on the existing and planned construction of the Jian-20, two engines per aircraft. This amount is enough to equip seven regiments of 24 fighters each. Representatives of the PLA Air Force and the PRC Defense Industry want to "push" the Russian side at the cost of the Al-41F1S, because they feel an urgent need for powerful engines, the resource and capabilities of which they know reliably. The Chinese military expects that with the workload under the Chinese contract, UMPO, NPO Saturn and other Russian enterprises will not be able to accept other orders. So 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 modernize the Su-30MKI. In other words, the Chinese are trying to block India's actions to maintain the combat readiness of its Air Force.
With the receipt of even half of the required number of Al-41F1S, Chinese engine builders will be able to get out from under the harsh criticism of the military-political leadership and will have time to complete their own WS-15 development. This engine does not provide the required power of 15,000 kgf / cm2, since it uses an outdated ignition system, and liquid cooling is used for the blades of the KVD (from a single crystal of the 2nd generation of the DD6 brand).Solid-cast KVD support elements made using powder casting are also problematic, such alloys are not reliable at high rotational speeds and react poorly to overheating. In addition, the pilots of the 7th test detachment of the PLA Air Force established that the WS-15 turbofan engine cannot be jammed and re-launched in flight. Chinese specialists continue to try to gain access to Russian technologies that allow the re-launch of the Al-41F1S at altitudes up to 3500 m.
In addition to the formation of fighter regiments equipped with the Jian-20, the Chinese need the Al-41F1C turbofan engines to re-equip the latest modification of the Jian-11DG fighter and for the Jian-16 fighter-bombers.
NEW RUSSIAN DEVELOPMENTS
The third stage of improvement of the Al-41 is precisely the modification of the Al-41F2 ("Product 30"). These turbofan engines on test benches provide power in afterburner mode from 10,800 to 11,000 kgf/cm2, and in afterburner mode – from 17,600 to 18,000 kgf/cm2. The discrepancy in the parameters indicates problems with the fuel equipment, which does not provide the necessary amount of fuel.
PLA Air Force specialists expect that the Russians will stabilize the thrust of the engines, and to increase the resource to 5000 hours, the maximum indicator will be reduced to 16,000 kgf / cm2. Al-41F2 has a high air consumption – 125 kg / sec, which is 27% higher than that of Al-31FP. Fuel consumption is 670 g/kgf. In this regard, the Chinese expect that the capacity of the Al-41F2 will be 20% higher than that of the Al-41F.
The assembly of the Su-57 at the enterprise in Komsomolsk-on-Amur (KNAAPO) will be carried out using Al-41F1S engines. The first serial Al-41F2 engines are to be delivered to the KNAAPO assembly line in 2025-2026 for the planned assembly of the Su-57M. According to Chinese experts, the assembly speed of the Su-57 at KNAAPO cannot exceed three aircraft per year.
According to the tactical and technical task (TTZ), the serial engine should provide the Su-57 fighter with the ability to fly in cruising mode at a supersonic speed of Mach 1.6, and the maximum speed should reach Mach 2.4. At the same time, the Russian military requires a reduction in time for maximum afterburner mode. Also, the serial Al-41F2 engine should provide the Su-57 with a thrust-to-weight ratio of up to 1.36 and a combat radius of 1200 kg with a full load of the internal rocket and bomb compartment.
The empty weight of the Su-57 is 18,000 kg, the normal take–off is 25,000 kg, the full take–off is 29,700 kg, the maximum (critical) take–off is 35,000 kg. The main disadvantage of the Su-57 is the low combat load – 4200 kg. This is one of the reasons why the PLA Air Force refuses to purchase this aircraft, but they really want to get the Al-41F2 engine.
PROBLEMS AND QUESTIONS
The main problem of Russian engines is insufficient overall resource and small repair intervals. The resource of Al-31FP is 1500 hours, the resource of Al-41F1C is 3000 hours. Al–41F2 should have a total resource of 5000 hours. The Chinese are forced to wait for the Al-41F2 to be refined to the required indicators. It is assumed that this indicator will be achieved through the use of a new single crystal of the 3rd generation of the DD9 brand and a new titanium-aluminum alloy for KVD blades.
The development and testing of pre-production samples of the Al-41F2 will allow Russian specialists to create a technical reserve for the power plant of a promising 6th-generation fighter. When creating it, Russian designers intend to use S-shaped air intakes that completely hide the engine blades from radar detection. Mathematical modeling has established that the S-shaped profile of the air intakes will reduce engine power, as the air passage time will increase. It's up to the test bench, which allows you to work out all the options.
These turbofan engines have already allowed us to collect information about the appearance of the power plant for 6th generation fighters. The promising engine will be three-circuit, which will increase its fuel efficiency in cruising mode. Also, a three-circuit air supply system will reduce the overall engine temperature and the thermal visibility of the aircraft (reducing the exhaust gas temperature due to purging from the third circuit).
The engine will be equipped with two-plane thrust vector deflection modules (OVT), worked out on the Su-27LL. Probably, the angle of deviation in the vertical plane will be 240 (according to other data, 260), since a change in the thrust vector by more than 300 worsens the controllability of the aircraft. Thanks to the engines with OVT, the Su-57 fighter is capable of turning around its own axis in a horizontal plane at a speed of 600 per second.
WHAT THE CHINESE ARE WORKING ON
Chinese experts admit that the resource of national-made OVT modules is only 50 hours (similar components of Russian production last from 150 to 200 hours and then require complete replacement). In addition, Chinese modules achieve thrust deflection in the vertical plane no more than 17 degrees, and in the horizontal no more than 15 degrees. Installation of the Chinese OVT module on Russian engines is impossible, since there is no single control unit and software. The Chinese do not have qualified designers in the field of OVT and, given the political situation, cannot rely on the help of Ukrainian partners. They intend to continue the search for technical specialists in the Russian Federation.
Attempts by the Chinese to copy American-made JT8D powerplants for their Hong-6 bombers were stopped after regular deliveries of D-30KP-2 turbofan engines. Such engines were equipped with IL-76T and IL-76MD transport aircraft acquired by the PLA Air Force Command in the 1990s. Chinese designers redesigned the engine compartments of the Hong-6 to accommodate the D-30KP-2, which were not originally intended for these aircraft.
By 1998, the Department of Weapons and Equipment of the PLA Air Force was convinced of the high cost of servicing the Il-76 in Russia. In the same year, the Chengdu Engine Corporation (420 Aircraft Engine Plant) sent a proposal to the PLA Air Force Command to transfer two D-30KP-2 engines to it for mastering the procedures for partial or complete repair and airfield maintenance. In turn, the Chinese military demanded that the engines, after disassembly, defects, maintenance and assembly, be installed on the prototype of the long-range bomber "Hong-6K" (Xi'an Aircraft Factory). The test squad of the Chengdu Aviation Enterprise handed over one IL-76T, from which the engines were removed for further study. It is worth clarifying that the Xi'an plant is able to assemble six Hong-6K bombers and six Yun-20 transport aircraft annually, as well as fulfill orders for other aircraft and export contracts.
The process of studying the D-30KP-2 by Chinese specialists took about two years (1998-2000). Meanwhile, as part of negotiations and consultations with the Russian side, information was collected on both D-30KP-2 and D-30KP-3 "Burlak". From 2009 to 2020, the Chinese side purchased 436 D-30KP-2 engines. The last contract for 54 engines was signed in 2018. Currently, the D-30KP-2 engines are equipped with Yun-20 heavy transport aircraft, which were adopted by the PLA Air Force in 2017.
Chinese specialists do not plan to continue purchasing the D-30PK-2 engine in Russia, since they have already partially received documentation for the more powerful D-30KP-3 Burlak engine. This documentation allowed the specialists of the 420 plant and the 624th Research Institute (Chengdu city) to develop a similar WS-18 engine. The military industry of the People's Republic of China has once again demonstrated the ability to master foreign technologies on the example of Russian aircraft engines.
In the absence of their own scientific school, Chinese specialists are still trying to carry out work in the field of engine building. We can carefully assume that we will see the first breakthrough achievements of Chinese engine builders in the next five to seven years.
Vasily Ivanovich Ivanov is a journalist.