Korea’s speed is amazing! The 4.5th-generation aircraft KF-21 first flew on July 19, 2022. Four prototypes have taken to the sky in less than half a year. Among them, the first flight of the second prototype is on November 10, 2022, the third prototype made its first flight on January 5 this year, and on January 17, after more than 80 test flights, the KF-21 , Breaking through the speed of sound for the first time, flying at an altitude of 12,000 meters. The latest news is that on the morning of February 20, its fourth prototype, the first two-seater aircraft, successfully achieved its maiden flight.
The fourth KF21 is a two-seater

Although many Korean media mistakenly called the KF-21 the second two-seater fifth-generation aircraft in the world, even juxtaposed with the two-seater version of the J-20, it is actually more like a two-seater trainer aircraft of the same type, that is, similar to the Su 27UB, not a command and control aircraft like the two-seat J-20. Of course, it is not ruled out that South Korea will forcibly add the function of commanding drones to it in the future, because it looks more like a fifth-generation aircraft.


During the previous nearly 100 test flights, KF-21 exposed many design problems. For example, during the third test flight of the first prototype, when the plane was still rolling on the runway, it detected “the abnormality of a specific system.” Circumstances” that prevented it from even taking off. According to media reports, similar failures occurred during the first two test flights, but South Korea ignored them for the sake of the so-called progress, and the third aircraft finally went on strike.
Although the KF-21 took off successfully during the fourth test flight, an alarm sounded in the air, causing the plane to land early. It is true that there will be various problems in the test flight of the new aircraft, which is expected, but the failure of the KF-21 is too frequent, and it even failed to take off for a time. This is not a small problem.
The most important thing is that once some problems are proved to be problems in aircraft design, especially structural problems, South Korea rushes to build many prototypes, even two-seaters, which may be overthrown and restarted. Haste makes waste. After all, before the KF-21, South Korea only had the experience of developing the T-50 advanced trainer and assembling the F-16, and there are still many detours that have not been taken.

For an aircraft positioned as “F-35 leftovers” the biggest problem with the KF-21 is not that it cannot be invisible without a built-in bomb bay, but that it adopts a static stability design, at least the static instability is relatively small. That is to say, it has not even reached the basic indicators of some third-generation aircraft. This is calculated by Fang Fang, a well-known aviation blogger, from the position of the main landing gear of the KF-21 and the take-off pull-up during the first flight.

Some people may say, as a 4.5th generation aircraft, how could the KF-21’s statically unstable design not even reach the level of the third generation aircraft? Could it be that some functions were locked during the flight test phase for the sake of caution? In fact, the KF-21 has now carried out nearly a hundred test flights, and the fourth prototype has flown into the sky. If the restriction function has not been released until now, it is enough to prove that South Korea has insufficient confidence in its domestic fighter.

Interestingly, “US News and World Report” recently released the latest power rankings of various countries. South Korea’s position has been greatly improved, surpassing Japan and France, and actually ranked sixth, second only to China, the United States, Russia, Germany, and the United Kingdom. It is generally suspected that the editor who made this ranking is Korean. In another statistical data, from 2017 to 2021, South Korea’s arms and defense product exports accounted for 2.8% of the global share, ranking 8th globally. South Korea also stated that it will occupy 5% of the global arms export market in 2027. Share, becoming the world’s fourth-largest arms exporter.

Obviously, KF-21 is an important support for South Korea to become “the world’s fourth largest arms exporter” and an important support for “the world’s sixth largest power”, but its exports may not be as optimistic as imagined. On the one hand, its positioning is “F-35 leftovers”, that is, to pick up some leftovers from F-35, which determines its market size; on the other hand, it is a dual-engine design, and the price will not Cheap, the Koreans themselves estimate that its unit cost will be twice that of the top-equipped F-16, that is, more than 100 million US dollars. Compared with the F-35, there is no price advantage, and it may even be more expensive, unless the South Korean government Subsidize again, otherwise, it is hard to imagine a third customer.