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KF-21 "Boramae" = "Falcon" or "Young Eagle"

The KF-21, a 4.5-generation fighter jet, is set to replace the Air Force's aging fleet of 3rd-generation fighters, the F-4 and F-5. Fourth-generation fighters are upgraded versions of 3rd-generation jets, equipped with precision-guided munitions. The 4.5-generation fighters like the KF-21 combine the hardware of 4th-generation jets with the software of 5th-generation aircraft. The KF-21 is a next-generation fighter that will replace the air force's long-running fighters and protect the airspace in future battlefields. It is the largest weapon system research and development project since the construction of the military, with a total of KRW 8 trillion in development costs, and is expected to be delivered to the Air Force after mass production.

South Korea’s 4.5-generation fighter aircraft research and development project was launched in 2001. After years of pre-research, the KF-X plan was finally officially launched in 2016, and it took 5 years for the prototype to come out. The total project funding reached 18.6 trillion won (approximately RMB 109 billion), and the research and development expenses alone reached 8.6 trillion won. Indonesia participated Part of R&D investment. This 4.5-generation fighter will replace the Korean Air Force F-4 and F-5 fighters.

The KF-21 is equipped with twin engines and applied low-observable technology. It is larger than the F-16 fighter with a fuselage length of 16.9 m, a wingspan of 11.2 m, and a height of 4.7 m, and is similar in size to the F-18 fighter. The maximum speed is Mach 1.81 (2200 km per hour), the range is 2900 km, and the armament payload is 7.7 tons. Its range is 2,900 kilometers and is equipped with air-to-ship missiles.

As of 2018 the design length was 16.8 meters, the wingspan is 11.2 meters, the height is 4.8 meters, and the maximum speed is Mach 1.97. Thhis compared with the F-18E, which had a length of 18.3 meters, a wingspan of 13.6 meters, a height of 4.88 meters, and a maximum speed of Mach 1.6. It can be seen that KF-X is shorter than F-18E, but the speed requirement is higher.

The KF-X’s weapons cannot be loaded internally, but can only be semi-conformally mounted externally. Under the all-air combat configuration, the stealth will be better than the F-18E, and the flight resistance will be lower. The KF-X had no requirement for ship-board landings. In terms of aerodynamics, it can be optimized in the direction of drag reduction without considering low altitude and low speed. In terms of structure, there was room for weight reduction, but the long range determines the amount of fuel in the aircraft.

In the pre-research, South Korea studied single-engine, double-engine, normal, duck-style, single vertical tail, and double vertical tail layouts. The National Defense Research and Development Agency (ADD) and the Korean Aviation Industry Corporation (KAI) have separately submitted plans. ADD's plan is more radical and tends to be dual-fired and full-loaded weapons, but the weapon mounting requirements were later relaxed to the first phase of external loading, and the second phase will consider internal loading; KAI's plan was relatively conservative, preferring single-shot and external weapons. The final plan seemed to be biased towards ADD, but KAI was still the general contractor of the manufacturer: dual-engine, dual-tail, and semi-conformal weapon.

The Garrett air inlet, which can effectively control the shape of the two-dimensional shock wave, is an improvement of the normal shock wave pitot tube air inlet, but the boundary layer separation channel not only increases the resistance, but also the radar reflection concentration area. The F-35, F-20, and "Falcon Eagle" DSI air inlets are more advanced, and the difference from Garrett is comparable to the difference in stealth design between F-22 and F-117.Compared with the diamond-shaped Garrett air inlet of the American F-22, the DSI air inlet of the J-20 omits the boundary layer partition and the vent, which greatly increases the effective working range. The air intake of the Russian Su-57 is a bit like Garrett, but the mechanism of shock wave control is not Garrett. The most important thing is the addition of adjustable side strips, which can not only act as a canard, but may also control the air inlet pre-compression and shock wave position and shape.

The cambered double vertical tails not only increase the aerodynamic control capability, but also the need for lateral stealth. However, both Su-57 and J-20 have adopted small-area full-motion double vertical tails. KF-X is still using the old large-area fixed double vertical tails plus trailing edge rudder surface, which not only increases weight and resistance, but is also not conducive to stealth.

South Korea ordered the F-35A, based on strategic and tactical needs, and possibly out of competition with Japan. But even without considering the cost issue, the single-engine F-35A is not ideal for South Korea, and South Korea prefers twin-engine fighters. North Korea’s air threat is low, and South Korea’s existing combat aircraft already have an overwhelming air superiority. However, South Korea has many mountains and lack of alternate airports. The high reliability of twin-engine fighters is more suitable for South Korea's needs.

In addition, South Korea’s ambitions were not limited to the Korean Peninsula. South Korea’s unilaterally delineated air defense identification zone overlaps with China and Japan and extends south to the sea off Shanghai. It also requires the range and reliability of dual-engine fighter jets to ensure effective control. F-15K was selected under this background. Unlike the U.S. Air Force F-15E, which focuses on air-to-ground operations, the South Korean F-15K is used as the main force for air superiority. Before the introduction of the assembled F-16, the dual-engine F-18 actually won the bid, but it was removed due to cost and bribery issues. This led to the single-engine F-16 being selected.

The United States strictly guards top military technology and refuses to export active electronic scanning radar, infrared photoelectric and electronic countermeasure technologies that are critical to KF-X. Lockheed also lacked enthusiasm for building potential competitors for F-35. South Korea turned to Europe, but Europe did not have mature stealth fighter technology. It was not South Korea’s intention to help others practice their hands at their own expense.

One problem is that the key to stealth fighters lies in the full internal loading of weapons, which has led to a series of problems such as volume, weight, and engine thrust. The semi-conformal plug-in is also called the semi-buried plug-in. This is not a new thing. The F-4 "Phantom" type has the ability to carry the AIM-7 "Sparrow" air-to-air missiles in a belly and semi-conformal mode. The F-15 is the same. The United Kingdom has a special liking for semi-conformal plug-ins. Typhoon uses semi-conformal plug-ins as the main means of mounting medium-range air-to-air missiles. Compared with the under-wing plug-in, the resistance of the semi-conformal plug-in, the radar reflection characteristics, and the roll inertia of the airframe are all reduced. However, the semi-conformal external hanger needs to leave a shallow cavity on the surface of the body for the weapon, which requires a higher matching of the size of the weapon and the cavity. Weapons that are too large will not work, of course, if they are too small, the matching will not be close, resulting in extra surface bumps, resulting in extra drag and radar reflection characteristics.

The semi-conformal plug-in is generally used for medium-range air-to-air missiles that are locked after launch, so the restriction on the seeker's horizon caused by the semi-conformal is not a problem. Short-range air-to-air missiles need to be locked before launch. The F-22 and F-20 have to spend a lot of time on this. The F-35 simply hangs under the wing, and the KF-X does not follow this.

The KF-X's power is positioned at 220kN level, which can only be achieved by a single-engine F135, but this is a pie in the sky and impossible. The United States is willing to provide General Electric F414 turbofan engines, which can almost reach the requirement of 220kN for dual engines. Power determines performance, which defines the possible performance range of KF-X. South Korea obtained the mainstream F414-400, with military thrust of 57.8kN, afterburner thrust of 97.9kN, and thrust-to-weight ratio of 9:1. The take-off weight and main tactical data of the KF-X have not been announced.

KF-X is one of the most important national project to replace current air force fighters and to introduce the next generation fighter that can satisfy the future operation concept of force battlefield. Also, KAI is under localization of major avionics part for product improvement by domestic technology. In addition, the core equipment AESA radar and EW Suite(Integrated Electronic Warfare Equipment), IRST (infrared search and track) and EO TGP(electro optical targeting pod) are Verify performance through functional check and ground test.

In addition, the KF-21 is a domestic fighter, capable of improving its own performance, and was designed with the evolutionary development in mind to integrate the domestically developed armament system into the aircraft. Stable supply and demand through localization of parts is possible in the future, which is expected to reduce operating and maintenance costs and maintain a high utilization rate.

Other than being able to engage in midair combat it can also disarm enemy advances via land and sea as well as destroy enemy's air defense networks. Long-distance air-to-ground missiles currently under development in Korea can be installed. Korea was also preparing for the new warplane to be able to be equipped with supersonic air-launched cruise missiles dubbed as a "game-changer" in war tactics. The fighter jet is equipped with locally developed state-of-the-art aviation electronics equipment.

This includes the Active Electronically Scanned Array or AESA radar system which are the eyes of the aircraft enabling the jet to detect and track multiple targets simultaneously. The beam of the radio waves is electronically steered to point in different directions without the need to move the antenna. The radar system is crucial in the identification of enemy forces during aerial warfare, and also enables fighter jets to track enemy forces during ground surveillance. The jet's AESA radar unit has been locally developed since 2016. Its developers aim to meet the requirements of the South Korean military equivalent to that of U.S.'s F-16 fighter jets, which are able to simultaneously detect up to 10 objects from 50 to 60 nautical miles away.

KAI is promoting the development efficiently and economically based on the technology secured by the development of KF-21 and the localization base of 65% based on the price of the first mass production unit. A total of 85 major items are being localized, including major avionics equipment such as AESA radar, EO TGP, IRST, and EW Suite.

• AESA: Active Electronically Scanned Array (Active Electronic Phased Array Radar)
• EO TGP: Electro-Optical Targeting Pod (Electro-Optical Targeting Pod)
• IRST: Infra-Red Search and Track (Infrared Ray Tracking Equipment)
• EW Suite: Electronic Warfare Suite (Integrated Electronic Warfare System)

KAI is developing more than 60 items of flight control and mission equipment software installed on the KF-21. In the past, when the T-50 advanced trainer was developed, it was an item that relied on foreign companies.

Along with the F414 engine provided by the United States, KF-X will use Israeli radar (possibly based on Elta EL/M2052), British "Meteor" medium-range air-to-air missile, and German IRIS short-range air-to-air missile. If approved by the United States, it may also be integrated. AIM-120 medium-range air-to-air missile and AIM-9X short-range air-to-air missile. The U.S. arms control has strict controls on radars and missiles, but is relatively loose on engines and aviation ad hoc equipment. KF-X bypasses American radars and can be used in weapons with the United States and Europe, increasing the export potential. KF-X will also use a large number of key systems directly from Europe and the United States, such as the United States United Technology’s environmental control system, the British Cobham’s oxygen production, missile pylons and ejection systems, communication-navigation-identification systems, auxiliary fuel tanks and underwing pylons , British Mackit’s brakes, etc. The Korea Aerospace Industries (KAI) KF-X fighter will have a two-seat version, developers confirmed in July 2017, following years of depictions of the indigenous aircraft with just one seat.

In addition to confronting real stealth fighters, quasi-stealth like the KF-X is already "enough" for typical air combat. It may not be a disadvantage to confront the F-35, which is lacking in air combat performance. With proper adapting devices, small-diameter bombs may also be mounted semi-conformally. In fact, the entire ammunition is already protruding from the surface of the body, but it is still hanging tightly. The drag and unfavorable aerodynamic interactions will be more significant, but they can still be overcome. In this way, KF-X also has a certain quasi-stealth air-to-ground attack capability.

Stealth is only one aspect of fighter performance. In order to ensure basic flight performance, reduce technical risks, ensure air combat performance, reduce air and ground requirements, and reduce stealth requirements, KF-X is a pragmatic approach. On this basis, it is hoped that in the case of little changes to the body, a conformal cocoon cover will be added to enable the original semi-conformal external air-to-air missile to be internally loaded, but a smaller diameter bomb with a larger diameter will not be easy to handle. There are gains and losses.

South Korea's homegrown KF-21 Boramae fighter jet has been given a tentative green light for combat suitability. The Defense Acquisition Program Administration on 16 ay 2023 announced that the evaluation was made following hundreds of ground and test flights carried out over the last two years. The agency says the provisional evaluation has laid the foundation to proceed with the initial mass production planned to begin next year. The fighter jet is capable of traveling 2,200 kilometers per hour and is equipped with advanced technologies that can track multiple targets.

Korea Aerospace Industries (KAI) said 25 June 2024 it had signed a 1.96 trillion-won ($1.41 billion) deal with the state defense procurement agency to start production of the next-generation KF-21 fighter jet. The contract with the Defense Acquisition Program Administration (DAPA) covers a total of 20 KF-21 units, including follow-up logistics support, such as technical manuals and training. KAI stressed the significance of the deal, as "it realizes the national aspiration for self-reliant defense by protecting our airspace with our technology."

South Korean defense firm Hanwha Aerospace Co. also announced separately that it has signed a 556.2 billion-won deal with DAPA to supply engines for the KF-21 from this month until December 2027. Hanwha Aerospace will deliver around 40 F414 engines, which will be installed in the KF-21, along with spare modules. The company will also provide follow-up logistics support, including engine maintenance manuals and on-site technical assistance. Hanwha System will supply active phase array (AESA) radar. The contract is worth 110 billion won, and it will be installed on KF-21 from the end of August 2025.

The final combat suitability evaluation was expected in 2026. Korean supersonic fighter KF-21 will enter Yangsan and will be deployed to protect Korean airspace sequentially from 2026.