South Korea’s 4.5th-generation aircraft KF21 will make its first flight next month. Recently, its ground tests have become more and more frequent. For example, after the No. 04 two-seater prototype was tested for the refueling device, on June 28, the No. 001 prototype was tested again. The engine was tested on the ground, and its APU ignition method made people feel familiar.
KF21APU fires at startup.
F22APU fires at startup. It is said that this is a startup failure?
That’s right, when the F-22APU started up, flames shot out diagonally from the back of the machine. It seems that the KF-21 is known as the low-end version of the F-22, and it really lives up to its name. I even learned this. However, the flames from the KF-21 APU, like the tail flame of its "World" rocket, are scattered and weak. Is this a common problem?
The flames are so scattered
The tail flame of Korean rockets is also very weak. Is this a common problem?
In addition, in the hangar in Alaska, there is a smoke pipe specially set up for the F-22 APU, which is like eating Korean barbecue . Why didn't KF-21 think of this? Moreover, when the F-22APU is started, there will be thick smoke billowing, like a hand-cranked tractor, or like "farting". I wonder if the KF-21 has learned these "real skills".
Want to eat barbecue? Does
F22 "fart" when it starts?
The so-called APU is an auxiliary power system. It can help start the main engine of the aircraft without relying on external equipment for power supply. The engine alone cannot start, or it can provide air conditioning and electronic equipment on the aircraft when the main engine is shut down. powered by. The reason why the F-22's APU billows with smoke when it starts is related to the design of its Garrett inlet and the engine.
This smoke is a bit loud
The reason is that the end of the air inlet is the power system of the F119-PW-100 smokeless engine. When the engine is started, the exhaust device must be used to remove the exhaust gas to avoid affecting the working status of the engine. And when F-35 and J-20, due to the use of the new DSI air inlet , this action is no longer needed.
F22's APU window
From this point of view, the KF-21APU should also "fart" when it is started, because it does not have DSI technology and uses a Garrett inlet similar to the F-22. Although the KF-21's engine is not F119-PW-100, the F414 cannot work when it is full of smoke, so the smoke should also be exhausted before starting the main engine.
KF21 dual-seat aircraft
In fact, it is a common phenomenon that stealth fighters use APU, but the flame and smoke exhaust methods are different. For example, in our J-20, the flame started by the APU is not upward, but discharged downward. Someone once photographed it Related photos. Bringing the APU greatly increases the self-protection capabilities of the fighter aircraft when deployed at remote airports, and they no longer even need to carry a power supply truck when transferring.
The J-20 APU starts to fire downwards
However, for the KF-21, the biggest problem is not the fire and smoke when the APU starts, but that it has basically no introduction to stealth design. Judging from the opened maintenance door of this machine, not only does it not use a sawtooth design, but it is still based on the thinking of the third-generation machine. There are too many openings and only the convenience of inspection and maintenance is considered. Stealth fighters generally balance openings and stealth, reducing openings. Even if they open, they will be as close as possible to the original hatch position.
KF21The way to open the maintenance port
The maintenance port of the Su 57
Aircraft stealth is not a simple matter. The design of the KF-21 basically ignores the control of the direction of specular reflection, and does not consider the control of the unexpected scattering direction caused by the traveling wave . High-frequency scattering caused by protruding objects is also beyond the designer's awareness. Although South Korea said that what is now available is only the first phase of the KF-21, and they will add a stealth bomb bay in the second phase, but in fact, the problem of the KF-21 is far more than just a stealth bomb bay. No matter what version, it is estimated that Its final stealth performance may not be able to match the Su-57.
KF21 can never become a true stealth aircraft, yes, it will never be
Of course, from the development of KF-21, we can also see the advantages of the Korean aviation industry, that is, the team is particularly young, just like Korean Aerospace, they are all young People are working, and if they are done well, their potential is endless. So what we have to do is break this development trend in South Korea. I guess the United States will think the same way.
The team is very young
