Military

The “hidden” wings of Fighters

On July 15, 2020, the State Intellectual Property Office officially announced the evaluation results of the 21st China Patent Award, and the design patent of “lift body strake wing canard layout aircraft” of Chengdu aircraft design and Research Institute of AVIC won the Gold Award. As a result, the “hidden” wings of lift body, strake wing and canard configuration have become the focus of aviation enthusiasts again. In this issue, experts are invited to interpret the relevant contents for you.

with the exception of a few vertical take-off and landing fighters that generate lift by changing the direction of airflow during takeoff and landing, most aircraft overcome gravity by generating lift force generated by wings in motion.

the causes of wing lift are complex, and there are many related theories. Few theories can completely solve all the secrets of lift generation. However, it can be determined that the lift of aircraft mainly comes from the pressure difference caused by the velocity difference between the upper and lower surfaces of the wing. The lift is related to the velocity of airflow, the density of air, the area of wing and the angle of wing.

of course, aircraft will encounter various kinds of resistance when flying, such as friction resistance, differential pressure resistance, induced resistance, interference resistance and wave resistance. Continuous optimization of aerodynamic layout, its role is to increase lift, thrust and safety, reduce all kinds of resistance.

aerodynamic layout is one of the important factors that determine the maneuverability of fighter. Compared with the wing, the lift body, strake wing and canard layout are not “conspicuous” and belong to the “recessive” wings of the fighter. In terms of function, they can be regarded as the “three treasures” of the aerodynamic layout of the mainstream fighters in active service, and they play an important role in the mainstream fighters in the world.

lifting body layout. Compared with the traditional wing design of aircraft, lift body is a completely different concept. It uses three-dimensional design of wing body fusion body to generate lift. This design can obtain higher lift force at lower speed.

the United States and the Soviet Union have started relevant research since 1957, when two scientists, eagles and Allen, accidentally discovered the advantages of this design. The 1 / 2 scale prototype X-33 and X-38 of the space launch vehicle “adventure star” in the United States all adopt lifting body configuration.

the third generation aircraft with lift body design include Su-27, MiG-29, etc.; among the four generation aircraft, there are F-22, F-35, su-57, etc., of which, the lift body design features of su-57 are more obvious, with wide fuselage, stronger lift and smaller resistance.

strake wing layout. As a design appeared in the mid-1950s, the strake wing is a pair of long, narrow, sharp leading-edge, large swept back slender wings extending from the root of the leading edge wing of the wing on the basis of the conventional swept wing or delta wing layout. Generally, the strake wing is designed to be fully integrated with the fuselage and main wing to form a composite wing, which can improve the maneuverability and post stall characteristics of the fighter, especially the lift of the aircraft. It is usually divided into wing and fuselage.

canard wing layout. Also known as front wing or front wing. As early as 1903, the Wright brothers’ aircraft used the front wing configuration. The feature of this configuration is that the horizontal stability surface is placed in front of the main wing.

the aircraft layout with canard wing is called canard layout. The representative aircraft types include some Russian Su-35, Su-34 and SU-30MKI, and European “typhoon”, “gust” and “Eagle lion” fighters.

some fighter canards cannot be operated, while others can be operated. Canards are maneuverable, such as “typhoon”, “gust” and “Gryphon” in Europe. These canards can not only generate vortex lift, but also improve the stability drop in transonic process. When landing, it can control the deflection angle of canard wing to act as a decelerator.

according to the installation position, canard can be divided into upper, middle and lower configurations. Considering factors such as lift and stall angle of attack, the upper canard and middle canard are often used in canard configuration aircraft.

different aerodynamic configurations have their own advantages in different flight states. With different operational requirements, the selection and combination mode of the “three treasures” of aerodynamic layout are also different.

strake wing and lift body combination. For fighter, the use of strake wing can improve the flight performance and overcome the shortcomings of conventional swept wing and variable swept wing aircraft in low speed characteristics, wave resistance and flight stability. The use of lift body can increase the effective space inside the fighter, reduce the flight resistance and improve the high-speed flight ability. Therefore, F-22, F-35, su-57, Su-27 and MiG-29 all adopt the layout of combining strake wing and lifting body.

the first successful strake wing with active control technology is the F-16 fighter, but the F-22 is the better combination of strake wing and lift body. The strake wing extends from the apex of the nose to the root of the wing, and integrates with the fuselage and the inlet to form a lifting body, which not only produces more lift but also increases flight stability.

canard wing and strake wing combination. In order to improve the lift coefficient, many modern aircraft choose the configuration of canard wing and strake wing. For example, some of Russia’s Su-35, Su-34 and SU-30MKI, as well as the “typhoon”, “gust” and “Eagle lion” in Europe.

this kind of aerodynamic configuration has better lift and agility. The canard wing is usually larger and separated from the wing. Under certain conditions, the additional lift generated by canard wing is larger than that of slender strake wing. In some cases, the strake wing can produce more lift than the canard wing. The combination of the two complements each other. In addition to increasing lift, canard is also conducive to maintaining flight stability and controllability.

the fourth generation fighters of the United States and Russia adopt the conventional aerodynamic configuration, but not the canard configuration. There are many reasons. One of the reasons is that it is more difficult to deal with flight control when using duck layout, and it will bring more difficulties to stealth design of fighters, so they avoid this layout design.

canard layout combination of lift body strake wing. In the design of aircraft aerodynamic layout, not only the maneuverability of aircraft, but also a series of problems such as stability, maneuverability, strength and stiffness should be considered. In particular, the modern aircraft pursues high maneuverability and high speed, which makes the aerodynamic layout more demanding.

there are few fighters in the world that adopt canard wing, strake wing and lift body aerodynamic layout at the same time. One of the main reasons is that the combination design is very difficult. However, Chengdu aircraft design and Research Institute of China Aviation Industry Corporation has obviously successfully overcome a series of related problems, which is also the reason for its design award.

to adopt canard and strake wing design, we must face the working matching problem of canard, strake and main wing. If they are used together with the lift body design, there will be more problems to be faced. Their size, shape, position and other parameters need to be accurately calculated and a large number of wind tunnel tests can be obtained. In this way, the combination can be optimized. What’s more, how to reduce weight while increasing efficiency, and how to balance weight and flight efficiency are also problems that designers must face. All of these will make the design more difficult.

the development of future fighters will focus on the improvement of all altitude, all-weather and all-round air combat capabilities. Some experts summed up its main characteristics as “six Super”, namely: Ultra flat shape, supersonic cruise, unconventional maneuver, ultra long range attack, super dimension object connection, and super domain boundary control.

Based on the expectations and understanding of the next generation fighters of various countries, it is speculated that the next generation fighters may be equipped with artificial intelligence and quantum radar, capable of carrying out combat tasks without participation, and can achieve hypersonic speed, enter and exit near space, and use weapons with new physical principles. Therefore, the key to the next generation UAV is to improve the performance of the next generation UAV, such as improving the performance of the UAV, improving the performance of the communication system. Among them, manned / unmanned control system, stealth and hypersonic flight performance will be based on the overall innovation of aircraft aerodynamic layout. This determines that the aerodynamic layout design will still be the “old proposition” in the new situation.

the lift body layout is a popular model for future fighters. The future fighter is expected to have a large payload, which requires the use of wing body integration of the lifting body layout, to increase the wing fuel load and fuselage lift. In view of the rapid development of detection technology, in order to improve the survivability in the battlefield, the future fighter will adopt more powerful stealth design, in which the supersonic tailless delta wing lift body design is very likely to be used in the aircraft layout, and the flat tail and vertical tail are completely eliminated. The design of lift body with full wing body fusion and high lift drag ratio can make the fighter obtain higher maneuverability and stealth ability.

strake wing configuration may be the standard configuration for future fighters. It is a typical design of the third generation high mobility fighter to adopt medium swept wing and enlarged strake wing. The fourth generation fighters, such as the F-22, have adopted the special strake wing layout, and the F-35 and su-57 have also adopted the special strake wing design, so they have excellent flight quality. The future fighter is generally an extension of the existing fighter technology. Therefore, the strake wing layout will still be an indispensable design for the future fighter, but its design will be more advanced and reasonable.

future fighters may also adopt the canard layout. The possibility of stall can be basically ruled out in the canard configuration, that is, the aircraft will not enter the “spiral”. In order to avoid the shortcomings of the traditional canard configuration, the future fighter may be designed as a lift body canard configuration, that is, the lift body fuselage can play the role of canard, so that the fighter can fly and maneuver at high speed. This layout may be the basis for future aircraft.

waverider configuration may be used in future fighter. The concept of waverider has been embodied in some hypersonic missiles. The next generation fighter has the characteristics of unmanned, high speed, high altitude, long cruise distance and strong penetration ability, so it is likely to adopt a aerodynamic configuration with high lift drag ratio and strong maneuverability. The shapes suitable for hypersonic vehicles include lift body, wing body fusion body, axisymmetric body of revolution, wave rider, etc. Therefore, waverider configuration may be one of the development trends of future fighter. Constellation

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