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From the time the Wright brothers invented the airplane to the present, in addition to aviation power, almost every major breakthrough in aviation technology is inseparable from the wing. The simplest one is the straight wing. The leading and trailing edges of the wing are perpendicular to the fuselage, and the wing is the same width from inside to outside. Such a wing has a simple structure, is easy to manufacture, and has a high efficiency in generating lift, but also has a large drag. The force arm of the lift makes the force on the wing root very unfavorable.

The picture above shows the simplest straight wing

In order to balance the lift distribution, improve the wing force design and reduce weight, the straight wing can have a little taper, gradually narrowing from the inside to the outside, improving the lift distribution, so that more lift is generated near the wing root, shortening the lever arm and reducing the wing root stress. Low-speed, simple small aircraft can use simple straight wings to reduce manufacturing costs, but slightly more ambitious straight-wing aircraft mostly have a certain taper.

The wings of the US C-130 with a slight taper are also considered straight wings.

A straight wing with a taper can have a slightly swept leading edge or a slightly swept trailing edge. There is a slight difference in aerodynamics between the two, but they are both essentially straight wings. When the speed increases significantly, the disadvantage of a straight wing with high drag becomes more obvious, especially when the speed approaches the speed of sound.

The taper allows the leading edge to be slightly swept back, like the DC-3

It is also possible to make the trailing edge slightly swept forward, like the C-130

As the plane moves forward, it exerts pressure on the air in front of it, just like the bow of a ship pushes away the waves in front of it. The pressure waves are transmitted outward layer by layer at the speed of sound, which is the dividing line of air properties. When flying at subsonic speeds, the air in front of it is pushed to the sides by the pressure waves in an orderly manner to make way for the plane. However, when the speed of the plane reaches the speed of sound, it is no longer possible for the pressure waves to catch up with the plane and separate the air in front of it in an orderly manner to the sides. Instead, the pressure waves are squeezed together and the density increases dramatically, like a hard stone wall. It is no wonder that the resistance of a transonic plane is soaring when it flies against a large invisible stone wall. This is the origin of the sound barrier.

This invisible stone wall is also called a shock wave

As the speed increases, the front of the shock wave becomes conical, and the angle of the cone increases with the speed, and the air behind the front returns to subsonic speed. If the straight wing is swept back like a swallow's wing, "hiding" behind the shock wave front caused by the nose, the shock wave drag caused by the wing itself can be avoided.

The uneven surface induces additional oblique shock waves

The German Adolf Bussmann proposed the swept wing in the 1930s, but it did not attract much attention at that time.

Of course, there is also the black technology that the head of state ordered.

But in fact, the role of swept wings in avoiding shock wave drag caused by the wings themselves has been manifested even before the aircraft speed reaches supersonic speed. The wing generates lift by accelerating the airflow on the upper surface to form a speed difference between the upper and lower surfaces, which in turn causes a pressure difference. At high subsonic speeds, the airflow speed on the upper surface of the wing can exceed the speed of sound. If a swept wing is used, the oncoming airflow is decomposed into a component perpendicular to the leading edge of the wing (normal component) and a component parallel to the leading edge of the wing (spanwise component) according to the sweep angle. The normal component generates lift, and the spanwise component does not generate lift. When the sweep angle is zero, the normal component is equal to the oncoming airflow; the larger the sweep angle, the smaller the normal component. In other words, by using a suitable sweep angle, the airflow on the upper surface of the wing of a high subsonic aircraft can be reduced to below the speed of sound in the normal direction to avoid shock wave drag.

The angle of the oblique shock wave is greater than the plane rotation angle. This is the relationship between the two.

The swept wing decomposes the velocity component in the wingspan and normal direction. The normal component is smaller than the original velocity, which delays the generation of shock waves.

Swept wings are widely used on transonic (0.8-1.2 times the speed of sound) and high subsonic aircraft, such as the J-6 fighter, various Boeing and Airbus passenger aircraft.

The MiG-15 and F-86 were the first generation of fighters to adopt swept wings. Both were high subsonic fighters.

The British Lightning, the American F-100, and the Soviet MiG-19 are the first generation of swept-wing supersonic fighters.

With the same wingspan, the delta wing has a larger wing area and greater lift; the longer the wing root, the less structural reinforcement is needed, and the lighter the weight is with the same wing area. On the other hand, the drag characteristics of the wing are determined by the relative thickness, that is, the ratio of the actual thickness of the wing to the chord length (the distance between the leading and trailing edges of the wing). The actual thickness and chord length of the wing vary with different wingspan positions, so the ratio of the thickness to the chord length at 1/4 of the wingspan is generally taken. The chord of the delta wing is longer, and the actual thickness is thicker when the relative thickness remains unchanged, which simplifies the structural design and manufacturing, which is conducive to weight reduction; it also increases the volume inside the wing, which is conducive to increasing the fuel capacity inside the aircraft.

The American F-106

After the 1950s, fewer and fewer supersonic aircraft used large swept wings, and most used delta wings. The J-8II and J-10 both have delta wings, and Europe's "Typhoon", "Rafale" and "Gripen" also have delta wings.

J-8IIM

J-10A

typhoon

gust

And...the glory of India's great Hindustan...

Next is the trapezoidal wing, but the delta wing has not dominated the world. During supersonic flight, the wing can avoid shock wave drag as long as it "hides" behind the front of the shock cone. In other words, a wing with a shorter wingspan can also achieve the effect of reducing drag. In order to maximize the wing area to ensure sufficient lift, the chord length of the wing can be increased, and even the straight trailing edge can be swept forward to form a stubby trapezoidal wing. The swept wing relies on the sweep angle to reduce drag, but the large sweep angle brings a large spanwise component, resulting in lift loss, especially at low speeds. The large sweep angle causes a large part of the oncoming airflow to be lost by "slipping shoulders", resulting in insufficient lift at low speeds. Therefore, the take-off and landing speeds of large swept-wing aircraft are generally relatively high, and the maneuverability is not good enough.

The delta wing has the same problem. In contrast, the trapezoidal wing does not rely on the sweep angle to reduce drag, so the sweep angle of the leading edge of the wing can be smaller, which is closer to the straight wing with the same wingspan in nature, and has better lift. However, the wingspan of the trapezoidal wing is limited, so the final result is not necessarily better than a large swept wing or delta wing.

The Pakistan Air Force is equipped with swept-wing J-6, trapezoidal-wing F-104 and delta-wing Mirage III. This picture shows the characteristics of all three.

Compared to delta wings, trapezoidal wings are less commonly used, but there are still some loyal believers, especially Northrop, the F-5 and F-18 are trapezoidal wings. Lockheed's F-104 is also a trapezoidal wing, but the F-22 has gone beyond the traditional trapezoidal wing and is between the trapezoidal wing and the delta wing.

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