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Recently, there has been more debate about the US F-22. As the first fourth-generation (new standard fifth-generation) fighter in history, the F-22 successfully combined maneuverability, agility, stealth, and avionics advantages for the first time. At the air show, the F-22 spurted out after burning flames, which was shocking. However, some experts said that some performance parameters of the F-22 were flooded, and some of the indicators were exceeded by the J-20. What is going on?

F-22

The argument originated from an interview. The well-known domestic military expert Fu Qianshao has repeatedly stated that the maximum lift coefficient of China’s J-20 is “the highest of all fighters at present.” This is not surprising. The J-20 is a collection of decades of aerodynamic technology in China. It incorporates duck wing and side wing design, and makes full use of the eddy current coupling increase.

It is unprecedented. (The maximum lift coefficient of the aircraft is the limit value in the lift curve, which is usually reached at low altitude, low Mach number, and high angle of attack, which can reflect some aerodynamic performance)

At the time, domestic scientific researchers were also surprised and confused. The F-22 was just a mid-swept angle butterfly wing. The outer edge of the inlet was considered for the side wing, and the vortex of the nose was not enough. so high?

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Fu Qianshao said that it was later learned that the actual maximum lift coefficient of the F-22 was actually only 1.5. In other words, the US propaganda was a deliberate injection of water over claiming F-22 max lift coefficient figure.

Fu Qianshao graduated from the famous Northwestern Polytechnical University, majoring in aerodynamics, and is an alumnus with the chief designer of Wei J-20. He started as an air force mechanic, invented more than a dozen aviation technology patents, and published thousands of books. Some senior military fans said that the domestic aerodynamic model of the F-22 was later restored and tested in wind tunnels. The maximum lift coefficient did not reach the promotion level of 2.0.

The design of the J-20 was just when the F-22 was close to production, and the high indicators announced by the F-22 would naturally affect the J-20. Some netizens joked that the J-20 was forced by the F-22 of the United States, saying that the J-20 design team started in hard mode, but it was finally made, so that the maximum lift coefficient of the J-20 really reached 2.0 level.

 

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However, it should be noted that the use of such an advanced and unique duck-type aerodynamic layout for the J-20 is the result of the accumulation of research foundations laid down by China since the 1970s. In fact, the J-20 not only has the highest maximum lift coefficient value among active fighters, but also the smallest supersonic flight resistance coefficient among the fifth-generation aircraft. It can be said that it is an optimal solution to the contradiction between low-speed maneuverability and supersonic cruise.

The maximum lift coefficient of an aircraft is the limit value in the lift curve, which is usually reached at low and medium Mach numbers and high angles of attack; however, whether it can be actually achieved and utilized is another matter. Regardless of the actual maximum lift coefficient, the F-22’s maximum available lift coefficient is still at least high through aerodynamic optimization and advanced fly-by-wire control; coupled with a powerful engine, it still achieves second-class maneuverability.

J-20 Stealth Fighter vs F-22
J-20 Stealth Fighter vs F-22

For example, the maximum lift coefficient of the “Dog Fighter” F-16 of the third-generation aircraft is about 1.4, but chattering and insufficient heading stability will occur at an angle of attack of 22 degrees. You can only add an angle of attack limiter to avoid runaway. The actual maximum The available lift coefficient is only about 1.2.

Similarly, the Su-27 also has a 27-degree artificial angle of attack limit; the theoretical maximum value of the lift coefficient of the Mirage 2000 delta wing is also as high as 1.6, but it is actually only available at 1.1 level. The best of the three generations is the F / A-18, with a maximum controllable attack angle of 40 degrees, but still unable to fully realize its aerodynamic potential.

In the design of four-generation aircraft such as the J-20, not only the aerodynamic foundation is a higher level, it reduces or even partially eliminates the risk of chatter and loss of control at high angles of attack. Unleashing aerodynamic potential. After all, the factors that affect aerodynamics, flight control, structural materials and other factors are very complicated. The technical background behind them is not the two theoretical indicators of the maximum lift coefficient.

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Another point is that the engine thrust will obviously affect many maneuverability indicators (not all), because the thrust-to-weight ratio is one of the three basic parameters of the aircraft. Frankly speaking, the relative backwardness of the power has indeed dragged the hind legs of the J-20; but this also means that once replaced with the same-level engine, the J-20 can better exert its aerodynamic advantages and have greater future potential. Recently exposed photos show that the J-20 has been replaced with a new Chinese engine, emitting a bright red flame, and Chinese power has taken on a large role.

All in all, the F-22 integrated maneuverability and stealth for the first time, and the design concept led the trend of the times; but it was limited to the design era of 1990, and some indicators were outdated and normal. The accumulation of J-20 technology, coupled with the advantages of latecomers, has led the new trend. Do not think it is incredible. Otherwise, how to explain that so many US and European six-generation aircraft programs in the past two years are similar to the J-20?

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