From paper airplanes to hypersonic speeds, how do aircraft wings evolve?

Produced by: Science Popularization China

Author: Wang Fengyi (Institute of Mechanics, Chinese Academy of Sciences)

Producer: China Science Expo

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In the journey of human exploration of the sky, wings, as an important component of aircraft, play a pivotal role. It is not only the core component of the aircraft to generate lift, but also the most direct factor affecting the shape of the aircraft. Today, let us walk into the world of wings and explore the scientific principles and wonderful designs behind them.

The Secret of the Wing: The Balance of Lift and Drag

The mystery of the wing is first reflected in how it helps the aircraft overcome gravity and soar into the sky. In flight mechanics, the wing supports the weight of the aircraft by generating lift. This lift is generated by the difference in air flow speed between the upper and lower surfaces of the wing. When the aircraft moves forward, the air above the wing flows faster, forming a low-pressure area; while the air below the wing flows slower, forming a high-pressure area. This pressure difference is the key to the wing's ability to generate lift.

Wing

(Photo source: veer photo gallery)

However, lift is not the only function of a wing. While pursuing lift, a wing must also face the challenge of drag. Drag is the obstacle encountered by an aircraft during flight, which consumes the aircraft's power and reduces flight efficiency. Therefore, in the design of a wing, how to find a balance between lift and drag has become the focus of scientific researchers.

What effect does wing shape have on flight performance?

The shape of the wing has a crucial impact on the flight performance of the aircraft.

We can get a glimpse of this from the example of paper airplanes. When we were young, we may have folded paper airplanes of different shapes, some with wide wings, some with slender wings. These different shapes directly determine the flight characteristics of paper airplanes.

In aircraft design, the most important parameter that determines the shape of the wing is called the aspect ratio , which is the ratio of the wing's span perpendicular to the flight direction to the chord length along the flight direction. This is the ratio of a and b in the figure below.

The original picture shows the J-35A fighter performing a flight show at the 2024 Zhuhai Air Show

(Photo source: Beijing Daily)

Wings with a larger aspect ratio appear particularly long perpendicular to the direction of flight, making the aircraft look wider overall; wings with a smaller aspect ratio are shorter perpendicular to the direction of flight, but slightly longer along the direction of flight, which, when combined with the fuselage, makes the overall shape of the aircraft look more slender.

The aspect ratio of aircraft is relatively large

(Photo source: veer photo gallery)

A typical example of a wing with a large aspect ratio is the Y-20 transport aircraft. Its design can provide strong lift, allowing the aircraft to carry more weight and fly farther. This design is particularly suitable for aircraft that require long flight time, long range, and large load, because they do not pursue flight speed too much, and carrying capacity is the primary consideration.

On November 23, 2023, the Y-20 aircraft carrying out the mission of welcoming the tenth batch of remains of Chinese People's Volunteers martyrs in Korea back to China landed at Shenyang Taoxian International Airport. The airport welcomed the volunteer martyrs home with the highest aviation etiquette of "passing through the water gate". Photo by Yu Hongchun

(Photo source: China Military Network)

On December 19, 2023, the Western Theater Command emergency command team boarded the Y-20 to rush to the front line of earthquake relief in Gansu. Photo by Liu Fang

(Photo source: China Military Network)

Small aspect ratio wings, as shown by fighters such as the J-20 and J-35, can reduce drag and increase flight speed. This design is undoubtedly the best choice for fighters that pursue high-speed flight.

On November 11, 2018, the J-20 fighter jet made its debut at the 12th China Air Show

(Photo source: Xinhuanet)

In addition to the aspect ratio, other design parameters of the wing, such as twist angle, dihedral angle and sweep angle, also have an important impact on flight performance. For example, applying a suitable twist angle can reduce the induced drag generated during flight; while increasing the dihedral angle can increase the lateral stability of the aircraft during flight, making the aircraft safer to fly.

Wing materials are ever-changing, and high-pressure capture wings have become a new highlight

With the continuous advancement of science and technology, the materials and technologies of wings are also constantly updated. Early aircraft wings were mainly made of wood, metal and other materials. Although these materials are strong and durable, they are heavy and limit the flight performance of the aircraft. Today, with the rapid development of composite material technology, wings have begun to use a large number of lightweight and high-strength materials such as carbon fiber and glass fiber. These materials not only reduce the weight of the wings, but also improve their fatigue resistance and corrosion resistance.

In addition, with the application of advanced technologies such as computational fluid dynamics and optimization design, the design of wings has become more precise and efficient. Researchers can use these technologies to refine the shape and structure of the wings to achieve the best flight performance.

Although significant progress has been made in wing design, researchers have never stopped exploring and innovating in the field of wing design. They are committed to developing more efficient and environmentally friendly wing designs to meet increasingly severe environmental and energy challenges.

Among them, the high-pressure capture wing, as a new hypersonic aircraft layout, is attracting widespread attention. In the traditional aerodynamic shape layout of hypersonic aircraft, there is a strong contradiction between the lift-to-drag ratio and the volume ratio, which means that the cost of hypersonic aircraft flying far and fast is a significant loss of loading capacity. This characteristic makes its engineering implementation full of challenges.

In response to this serious problem, the Institute of Mechanics of the Chinese Academy of Sciences proposed a new layout plan for a high-pressure capture wing configuration . By "capturing" the high-pressure area formed by the compression of the upper wall of the fuselage, considerable lift compensation can be obtained. According to the principles of aerodynamics, the volume of the fuselage increases, the strength of the high-pressure area formed by compression increases, and the lift compensation obtained is further increased, which ingeniously alleviates the contradictory relationship between the volume ratio and the lift-to-drag ratio.

After several years of hard work, the research on this configuration has made great progress. In 2018, the Institute of Mechanics published a cover paper titled "Hypersonic I-shaped aerodynamic configurations" in SCIENCE CHINA Physics, Mechanics & Astronomy, which attracted widespread attention from researchers at home and abroad. In 2020, the Institute of Mechanics conducted a wind tunnel test on this configuration at Mach number 6. The results showed that compared with the mainstream high-performance waverider configuration designed by a foreign country, the maximum lift-to-drag ratio and its corresponding lift coefficient increased by 5% and 86% respectively, and the volume ratio increased by about 10%, which strongly proved the potential of this configuration in aerodynamic performance.

In 2021, the Institute of Mechanics conducted the "Yufeng-1" flight test on the high-pressure capture wing configuration, and obtained real flight data of this configuration for the first time, providing support for more in-depth optimization design research.

This design, by cleverly utilizing the shape and structure of the wing, significantly improves the flight lift while bearing the flight resistance brought by the large volume, thus alleviating the contradictory relationship between volume and lift-to-drag ratio in traditional designs. This innovation not only improves the overall flight performance of the aircraft, but also opens up a broader development space for the future aerospace industry.

Schematic diagram of high-pressure capture wing configuration

(Image source: Acta Aeronautica Sinica)

In addition to high-pressure capture wings, researchers are also exploring a variety of other new wing designs, such as deformable wings, smart wings, etc. These designs change the shape, structure or function of the wings to adapt to different flight environments and mission requirements, providing more possibilities for the future development of aircraft.

Conclusion

The wing is not only the core component of the aircraft, but also the crystallization of human wisdom in exploring the sky. From the original wooden wing to today's composite wing, from simple shape design to complex structural optimization, the development of the wing has witnessed the persistent pursuit and unremitting efforts of mankind for the dream of flying.

In the days ahead, with the continuous advancement of technology and the emergence of innovations, the design of wings will be more efficient, environmentally friendly and intelligent. It will continue to lead humans to cross the sky, explore the unknown world, and write a flying legend for mankind.