"People's Liberation Army Daily" published a speech by Gong Feng, deputy chief designer of the J-20, on the 19th, which mentioned that the J-20 was finally replaced by a domestic engine 10 years after its first flight. Some analysts said that the maximum thrust of the domestic engine used by it reached 14.5 tons, which was already comparable to the 117S engine used by the Su 35S, showing that after more than 30 years of development, the Taihang engine has gradually entered a better state. However, the Taihang engine is not the original supporting engine of the J-20, and the supporting turbofan 15 engine is needed to fully release the full potential of the J-20. Today, let's briefly review the J-20's bumpy hair change process.
The first replacement of the J-20 - Russian AL-31F-M1 emergency
As Gong Feng, deputy chief designer of the J-20, mentioned in his speech, "The engines of the past (Russian-made engines and domestic Taihang) were not tailor-made for the J-20. On the one hand, we have to think of many ways to adapt the aircraft to the engine to meet the needs of combat. On the other hand, the aircraft had to make some concessions and compromises."
All along, the J-20 has been waiting for a suitable engine. However, this is also understandable, after all, the development time of advanced aero engines is very long, and the successful development of the F-119, the supporting engine of the American F-22, took 12 years to successfully develop, and it took another 8 years to reach the mass production standard, a total of 20 years. However, unlike the "F-22 and the supporting F-119 engine developed at the same time" adopted by the United States, the turbofan-15 was developed in 2006, which is exactly 9 years later than the J-20, and the delivery of the demonstrator was in 2011, almost at the same time as the test flight of the J-20 prototype. However, it is possible that we really underestimated the difficulty of the development of the fifth-generation fighter engine, and the subsequent development of the J-20 and turbofan-15 engines gave people a feeling of "parting ways" for a long time. The J-20 took off for the first time on January 18, 2016 and made its public appearance at the Zhuhai Airshow in the same year. On July 30, 2017, the J-20 participated in the battlefield parade marking the 90th anniversary of the founding of the army, and on February 9, 2018, it was officially installed as a combat unit.
The supporting turbofan-15 has encountered too many problems, which has also led to the J-20 having to urgently "change", using Russian engines from the first prototype to emergency. The engine model is "AL-31F-M1", which is a small optimization and improvement of the AL-31F engine by the Russian "Salyut" production enterprise, and the national finalization test was completed in 2005.
The military thrust of the AL-31F-M1 engine increased from 7.7 tons to 8.25 tons, and the maximum afterburner thrust increased by 1 to 13.5 tons. At the same time, the fuel consumption of the AL-31F is about 0.78kg/kgf.h, and the AL-31F-M1 is reduced to 0.77kg/kgf.h, and the service life is extended to 4000 hours. However, the price paid was that the fan size increased from 905 mm to 924 mm, and the weight increased from 1.49 tons to 1.52 tons accordingly.
AL-31F-M1 engine
Combined with the news of Russia and other media, China should have selected this engine as a transitional model before 2011, and purchased a small amount for prototype test flight. The AL-31F-M1 engine was then purchased in bulk from 2014 to equip the first mass-produced J-20.
Although the use of Russian-made engines solved the urgent need, the first batch of J-20s were also successfully put into service. But the AL-31F-M1 engine is only an engine developed in the 1970s and 1980s, which cannot really play the performance of the fifth-generation aircraft, and the most important point is that it cannot make the J-20 have the same super-patrol performance as the F-22 (Mach 1.5 flight for 30 minutes). Let's use the F-22 data to derive a simple deduction.
The weight data of the J-20 is not officially given, but the official gives the size data of the J-20: the fuselage is 21.2 meters long, 4.69 meters high, and the wingspan is 13.01 meters. The size data of the American F-22 is: fuselage length 18.92 meters, height 5.08 meters, wingspan 13.56 meters. Obviously, the J-20 is longer and taller than the F-22, but it is not as wide as the F-22. Here we assume that the weight of the J-20 is equivalent to that of the F-22, that is, the normal take-off weight is about 25.77 tons (52% internal oil), and the maximum take-off weight is about 37.6 tons. The F-119-PW100 engine is known to have a single military thrust of 105KN, and the F-22 supercruiser has a thrust-to-weight ratio of 0.83. To put it simply, as long as the J-20 can reach 0.83 at the normal take-off weight, it can achieve a super-patrol capability comparable to or even stronger than the F-22. It is known that the J-20 is equipped with a Single Military Thrust of the Russian AL-31F-M1 engine of 8.25 tons, and the calculated military thrust-to-weight ratio is only 0.64, although with a more slender fuselage and a better aerodynamic layout, the J-20's transonic drag is lower than that of the F-22, but it is generally believed that the super-patrol capability of the J-20 equipped with Russian engines is still weaker than that of the F-22.
Russian version of the J-20
In addition, because the engine is not domestic, the "full-authority digital engine control" (FADEC) of the AL-31F-M1 engine cannot be integrated with the fire control system of the J-20 (Russia is likely not to cooperate), so the Russian version of the J-20 does not support the iconic "flying fire push integration" technology of the fifth-generation aircraft, and there is a huge gap in the performance of the complete version of the J-20.
Of course, the Russian version of the J-20, with its excellent "stealth performance, super perception ability and supersonic mobility", can still easily kill the fourth/fourth generation half fighter in the super visual range air battle. On September 14, 2020, the official media "Jiefangjun Bao" reported on a brigade of the Eastern Theater Air Force, which mentioned that Chen Xinhao, the pilot of the brigade's "Wang Hai Brigade", "shot down 17 enemy planes" in one fell swoop at the cost of "zero damage" during a confrontation training. The "Wang Hai Brigade" is the first batch of units of the mainland air force to change into J-20s. This also shows that in the confrontation with non-stealth fighters, the engine will not become the shortest plank of the barrel.
The second change of the J-20 - the domestic Taihang engine is in place
It is also because it cannot be integrated with the fire control system, and in order to avoid large-scale mass production of the J-20 because the engine is pinched by Russia. The mainland began the second remake of the J-20 to adapt it to the domestic turbofan-10 engine.
After 18 years of development, the Taihang engine was designed and finalized in 2005, and then began to be installed on the J-11. However, according to the objective law, a newly designed engine has a process from design to maturity, and in the early stage of use, the Taihang engine also has a large number of problems, spending a lot of time and energy to solve one by one. In fact, even the J-11B and J-10B/C that are matched with the Taihang engine still use Russian engines at the beginning.
According to the analysis of public information on the Internet, the first batch installation of The Taihang engine was on the J-16, which entered service in 2016. For the sake of reliability, the J-10C, which was in service at almost the same time as the J-16, will not begin to be fully equipped with the Taihang engine until 2020. That is to say, the real maturity of the Taihang engine is in 2020.
The Taihang engine was adapted to the J-20 in 2017, by the J-20 numbered 2021, and this J-20 also became the first 100% domestically produced J-20.
However, considering the huge difference between the fifth-generation machine and the fourth-generation aircraft, it was not until last year that the mass-produced version of the J-20 began to be fully equipped with domestic Taihang engines, becoming the latest model to be equipped with Taihang engines in China. As for how to distinguish between the J-20 using the Russian engine and the J-20 using the Taihang engine, the method is very simple, look at the engine tail spout, like the following figure, the tail nozzle is jagged, even if the J-20 using the Taihang engine, there is no Russian version.
Taihang version of the J-20
The reason why the J-20 replacement will take 4 years, mainly because the replacement is a matter of one hair and one body for the J-20, and the "airframe, structure, pipeline, circuit, each subsystem and subsystem" of the aircraft must be redesigned.
What impact will the replacement of the domestic Taihang engine have on the J-20? The first is that the production quantity will no longer have the risk of being stuck in the neck of others, and the production will be as much as you want. Secondly, the Taihang version used by the J-20 belongs to the improved model, the maximum push of a single unit reached 14.5 tons, reaching the level of the three-stage AL-31F-M3 engine, the total thrust increased by 2 tons, so the acceleration performance, climbing performance and even the performance of the stable disk and the instantaneous disk of the Taihang version of the J-20 have not been small, plus it is a pure domestic engine, the engine's "FADEC" and fire control system can be seamlessly integrated, and the Taihang version of the J-20 has achieved "flying fire integration". Although there is no thrust vectoring technology for the time being, the Close-range combat maneuverability of the Taihang version of the J-20 is still much better than most fourth-generation/fourth-generation half-generation fighters. The J-20, which has China's "heart", has finally achieved "the unity of body and mind, both inside and outside, and both gods and forms"!
Of course, the disadvantages still exist, that is, because the military thrust of the engine has not increased compared to the AL-31F-M1 engine, the supersonic cruise capability of the Taihang version of the J-20 has not been improved, and it is still unable to compare with the F-22.
When will the third haircut arrive?
As Gong Feng, deputy chief designer of the J-20, mentioned in his speech, if we can use advanced domestic engines, it will free the J-20 from the shackles and release greater potential. So when does the J-20 need to be replaced by a turbofan-15 engine? Liu Daxiang, an aviation power expert and academician of the Chinese Academy of Engineering, once mentioned at a public meeting in 2018 that the fourth-generation turbofan engine (turbofan-15) in the mainland will be finalized in four or five years, that is to say, the turbofan-15 engine will be finalized as soon as this year, and the slower will be finalized next year. Referring to the time from finalization to installation of the F-119 engine in the United States, the large-scale installation of the turbofan-15 may take several years.