Advanced assembly ≠ independent research and development South Korea's new generation fighter plans to move forward with difficulty ■ Zhu Jinbo Kf-21 fighter renderings. Data picture Last month, the South Korean Ministry of Defense announced the medium-term national defense plan for 2022-2026, which plans for the construction and development of the South Korean army in the next five years. The South Korean military proposed that the future national defense budget will mainly invest in the development of advanced weapons and equipment such as kf-21 fighters. South Korea's kf-x stealth fighter project has a long history. The kf-21 mentioned this time is the first prototype developed by Korea Aerospace Industry Corporation for the project. According to the analysis of some experts, South Korea's development of kf-x fighter is based on two considerations: one is to promote the development of its national defense industry, and the other is to replace the old models such as American F-4 with kf-x fighter. Kf-21 fighter is regarded by the South Korean military as the backbone of future air combat. Considering the actual level of South Korea's national defense industry, can the model meet the design requirements in the future, and can the new fighters be loaded into the South Korean Air Force as planned? See the interpretation. From kf-x to kf-21, the R & D threshold of the fifth generation machine is high Since the kf-x stealth fighter project was proposed in 2001, it has encountered many problems in technology, technology and capital, and has been uneven all the way. In order to ensure the normal progress of the project, Korea Aerospace Industry Corporation proposed to reduce the kf-x to a fourth generation and a half fighter and continue its research and development. Even so, the project's first prototype kf-21 was reluctantly offline until April this year. Behind the poor progress of kf-x stealth fighter project, it reflects the practical problems such as complex technology and difficult development of the fifth generation fighter. Since the first flight of the U.S. F-22 fighter, only a handful of countries have been able to successfully develop the fifth generation fighter for more than 20 years. To successfully develop the fifth generation aircraft, we need to cross multiple thresholds—— One is the stealth function. The fifth generation aircraft highlights the stealth function, which requires a very high manufacturing level. The stealth function of landing gear, vertical tail, main wing, tail nozzle and other components should be considered. Any subtle process defect will increase the radar reflection area and expose the flight trajectory of the fighter. According to Russian media reports, under the condition of greatly improving the mobility performance, the su-57 forward radar reflection area is 0.5 square meters, only one percent of that of the Su-27. The second is engine technology. On the one hand, the engine of the fifth generation aircraft should have the function of vector propulsion, that is, the additional control torque is obtained through the deflection of the tail nozzle to realize the control of aircraft flight attitude change; On the other hand, we should consider reducing the infrared radiation of the engine to prevent the opponent from detecting the hot wake by using the infrared search and tracking system. The F-22 fighter is equipped with two F119 turbofan engines with high thrust and thrust weight ratio coefficients. In the case of afterburner, the maximum speed of the fighter can reach Mach 2.25. The third is the performance of radar system. Compared with the fourth generation aircraft, the airborne radar system of the fifth generation aircraft has been fully upgraded - the target detection performance, target capacity and reliability have been greatly improved. Taking the "squirrel" radar equipped with su-57 as an example, each antenna array has hundreds of radar wave radiator units. Each radiator unit can independently transmit and receive radar signals, scan the surrounding airspace 360 degrees and monitor ground targets at the same time. It can be said that most of the equipment components of the fifth generation machine are the crystallization of high technology, behind which is the embodiment of a country's comprehensive strength. In addition, the high R & D and use cost is an important threshold to be crossed in the development of the fifth generation machine. The fifth generation aircraft has adopted a large number of new technologies and new components in terms of engine, radar system and stealth materials, and the R & D and use cost is more than twice that of the fourth generation aircraft. Take Lockheed Martin F-35 fighter as an example, the R & D capital is more than 50 billion US dollars. The purchase price is about US $100 million, plus subsequent costs such as maintenance and system upgrade, the life cycle cost of an F-35 fighter is about US $373 million. Such "money burning" projects are unbearable for many countries. Kf-21 has low technical indicators, which is more like the "slimming version" of F-22 In recent years, South Korea has vigorously developed its national defense industry. Its armor equipment, ships and fighters have been exported to many countries and become a rising star in the international military trade market. However, the weapons and equipment produced by South Korean military enterprises have always inherited the technological genes of Europe and the United States, and the degree of national defense industry autonomy is not high. The engine, radar system and ejection seat of fa-50 light fighter manufactured by Korea Aerospace Industry Corporation are all products of European and American countries. The airborne weapon design is also completed with the participation and assistance of foreign military enterprises. Kf-x stealth fighter project involves many high-end technologies, which is an unprecedented challenge for Korean military enterprises. In the short term, Korea Aerospace Industry Corporation can not change the current situation of being controlled by others. It needs technical assistance from European and American countries in key areas such as avionics equipment, power system and pneumatic layout. This means that with the current technical strength of Korea Aerospace Industry Corporation, there is still great uncertainty whether kf-21 can meet the expected design requirements. From the off-line prototype kf-21, the bullet free cabin design of this model still adopts external and semi buried weapon carrying systems. When kf-21 external weapon flies, the center of gravity and aeroelasticity of the fuselage will inevitably be affected, which restricts the maneuverability of the fighter. In fact, both the aeroelastic design of the cabin door and the design of the mounted launcher are extremely complex projects in the research and development of the fifth generation aircraft. Obviously, with the current technical strength of Korea Aerospace Industry Corporation, it is not enough to complete the relevant design independently. Although the fuselage design of kf-21 is highly similar to that of F-22 fighter - it adopts Garrett inlet, double vertical tail double engine single seat layout and vertical tail trailing edge forward sweep design, its overall stealth ability still lags behind the latter. First, external weapons and aerial guns on the right side of the fuselage without stealth treatment will increase the radar reflection cross-sectional area of the fuselage; Second, the fuselage stealth coating is the core secret of various countries. The development process is time-consuming and laborious. It is difficult for South Korean military enterprises to make a substantive breakthrough in a short time. South Korean officials announced that kf-21 is a multi-purpose fighter with strong air, ground and sea attack capabilities. However, it can be seen from Korean media reports that the first batch of kf-21 is mainly loaded with "meteor" medium and long-range air-to-air missiles and "yieryist" short-range air-to-air missiles, and is not equipped with precision guided bombs, cruise missiles and other weapons, which greatly limits the ground combat capability of this model. It can be said that the first batch production model kf-21 is more like the "slimming version" of F-22, which is still a distance from the standard fifth generation machine. It is difficult to predict whether 40 new fighters will be delivered in the next seven years At the beginning of the development of the kf-x stealth fighter project, it was highly expected by the South Korean military. In order to reduce the risk of capital investment, South Korea proposed to jointly develop with Indonesia. Although seeking assistance can solve the urgent need, considering the difficulty of developing the fifth generation machine, it is difficult to predict whether the plan can be smoothly promoted. First, there is a lack of guarantee of funds. In May 2010, South Korea and Indonesia signed a memorandum of understanding on joint development of fighter aircraft, stipulating that the development cost of the project shall be borne by South Korea and paid by Indonesia. However, in recent years, Indonesia's military spending has been insufficient, and it is unpredictable whether the funds can be approved on time. In the early design stage of the project, Korean military enterprises can still fill the capital gap. Since they have entered the real machine verification stage, the project cost is even more stretched. Second, the introduction of technology is blocked. For the sake of confidentiality and security, some European and American countries are wary of technology diffusion and transfer, and set restrictions everywhere on military industrial cooperation projects. As early as 2014, Lockheed Martin promised to transfer a number of key technologies of stealth fighter to South Korea, but some core technologies have not been fulfilled so far. Third, the market competition is fierce. At present, the sales of five generation aircraft in the international military trade market are hot. Although the performance of kf-21 can not reach the standard of the fifth generation aircraft, it is quite close to the enhanced F-16 fighter. Some analysts pointed out that once the kf-21 enters the export stage, it will compete with the F-16 fighter in the international military trade market, and the United States is likely to restrict the export of the aircraft by cutting off the supply of engines. In fact, in recent years, Korea Aerospace Industry Corporation has been committed to improving the availability and reliability of kf-21 fighter and demonstrating the development cycle in detail. According to Korean media reports, kf-21 is expected to fly for the first time next year. The first mass production machine will be completed before 2026, and the first batch of 40 will enter the delivery stage in 2028. However, the final realization of the project mainly depends on the technical strength of South Korea's national defense industry. Therefore, in recent years, the Korean government has successively promulgated a series of documents such as the core technology plan for 2021-2035 and the science driven future national defense development strategy, actively formulated the future national defense innovation and development plan, and accelerated the smooth landing of the kf-x stealth fighter project. (outlook new era)