What is an Airfoil?

The wing is one of the important parts of the aircraft and is mounted on the fuselage. Its main function is to generate lift. At the same time, it can also set ammunition silos and fuel tanks inside the wing. It can store landing gear in flight. In addition, flaps to improve take-off and landing performance and ailerons for lateral control of the aircraft are installed on the wing, and some also have slat wings to increase lift.

The wing is one of the important parts of the aircraft and is mounted on the fuselage. Its main function is to generate lift. At the same time, it can also set ammunition silos and fuel tanks inside the wing. It can store landing gear in flight. In addition, flaps to improve take-off and landing performance and ailerons for lateral control of the aircraft are installed on the wing, and some also have slat wings to increase lift.

Chinese name

Wing

Foreign name

wing

main effect

Generate lift

Classification

Straight wing, swept wing, delta wing

Parts

Wing knife, twist

Structure

Consists of surface skin and internal skeleton

Wing basic information

Wing English

wing

Wing Introduction

The main component of an aircraft used to generate lift. Generally divided into left and right wings,

Symmetrically arranged on both sides of the fuselage. Parts of the wing (mainly the leading and trailing edges) can move. The pilot can manipulate these parts to change the shape of the wing and control the distribution of wing lift or drag to achieve the purpose of increasing lift or changing the attitude of the aircraft. The active wing surface (Figure 1) commonly used on the wing has various front and rear edge lifting devices, ailerons, spoilers, speed reducers, lifting ailerons, etc. The inside of the wing is often used for fuel. Where the wing thickness permits, the aircraft's main landing gear is often fully or partially housed within the wing. In addition, many aircraft engines are either straight

It is fixed on the wing, or hung under the wing.

The role of the wings is to generate lift to support the aircraft in the air. It also plays a certain stabilizing and manipulating role. The plane shape of the wing is various. Commonly used are rectangular wing, trapezoid wing, swept wing, delta wing, double delta wing, arrow wing, side wing, etc. Modern aircraft are generally monoplanes, but biplanes (two wing superimposed on top and bottom), triplanes, and multiwings have been popular in history. According to the connection of the wing of the monoplane to the fuselage, it can be divided into lower single wing, middle single wing, upper single wing and

Wing picture appreciation (20 photos)

Umbrella-type single wing (that is, the wing is above the fuselage, and the wing and fuselage are connected by a set of struts).

Wing classification

Wing Introduction

The main geometric parameters describing the wing shape are wingspan, wing area (wing pitch projection area), sweep angle (mainly leading edge sweep angle, 1/4

Chord sweep angle, etc.), upside-down angle, wing section shape (airfoil), etc. (Figure 2a). Commonly used basic airfoils include low-speed airfoils, peak airfoils, supercritical airfoils, and supersonic airfoils with sharp leading edges. In addition, there are some important relative parameters: chord ratio: the ratio of the wing span to the average chord length (the wing area is divided by the wing span); Ratio; relative thickness of the airfoil: the ratio of the maximum thickness of the airfoil to the chord length.

These parameters have important effects on the aerodynamic characteristics of the wing, the wing load and the structural weight.

The wing of an aircraft can be divided into three basic types according to the shape of the plane when viewed from the top.

Wing

Straight wing

The 1/4 chord sweep angle of the wing is below about 20 °. Straight wing is mostly used in subsonic aircraft and some supersonic fighters. On subsonic aircraft, the aspect ratio is about 8-12, and the relative thickness is 0.15-0.18. On supersonic planes, the aspect ratio is 3 to 4, and the relative thickness is about 0.03 to 0.04.

Wing swept wing

The sweep angle of the 1/4 chord of the wing is more than 25 °. Used for high-subsonic aircraft and supersonic aircraft. Commonly used parameter ranges of swept wings of high-subsonic aircraft are: swept angle of 30 ° to 35 °, aspect ratio of 6 to 8, relative thickness of about 0.10, and tip-to-root ratio of 0.25 to 0.3. For supersonic aircraft, the sweep angle exceeds 35 °, the aspect ratio is 3 to 4, the relative thickness is 0.06 to 0.08, and the tip-to-root ratio is less than 0.3.

Wing delta

The leading edge of the wing has a swept angle of about 60 °, and the trailing edge has almost no swept. The aspect ratio is about 2 and the relative thickness is 0.03 0.05. Mostly used for supersonic aircraft, especially for tailless aircraft.

Measures to Improve Aerodynamic Characteristics of Wings The short-sweep and triangular-thin wing commonly used in supersonic aircraft have the disadvantage of poor low-speed and high angle-of-attack characteristics. In the design of the wing, in addition to the proper selection of the shape parameters, the following additional measures are often adopted.

Forward swept wing

The structure of the forward-swept wing is the same as that of the backward-swept wing. The structure and load-bearing method of the root area of the wing is different from that of the straight wing. Except for single-beam wing, compared with the force form of the swept-wing structure, the load on the front beam root and the wall plate near the root of the forward-sweep structure are larger. The loading of the front beam is caused by the unloading of the longer (lower stiffness) rear beam.

Wing parts

Wing wing knife

A vertical slice with a certain height is arranged on the upper surface of the wing in the direction of the airflow (Figure 3a).

The wing knife is mainly installed on the swept wing. It can prevent the low energy airflow (surface layer) on the wing surface from converging to the wing tip, and also change the distribution of the wing lift in the span direction, so it can be avoided at high angles of attack. The disadvantage is that the wing tips start to stall first. The wingtip of the swept wing is behind the center of gravity of the aircraft. The stalling of the wingtip at high angle of attack will not only cause the aircraft to tilt (it is unlikely that the left and right wings will stall at the same time in actual flight), but also cause the aircraft to look up, making the aircraft go further Stall and lose control, so try your best to avoid it. The height, length, and number of wing knives, as well as the positions in the span and chord directions, need to be determined through experiments.

Wing twist

Wings whose chords are not in the same plane are called twisted wings. On swept wing, the wing tip profile is usually twisted downward relative to the root profile to reduce the wing tip profile angle of attack (negative twist). In this way, reducing the lift of the wing tip can prevent the wing tip from starting to stall first, which is called geometric torsion. On some wings, although the chords of all sections are in the same plane (no geometric twist), asymmetric airfoils with different cambers are used in the span direction. From the point of view of aerodynamics, it actually has the same function as geometric torsion and also controls the wingspan to lift distribution. This situation is called pneumatic torsion. On actual wings, aerodynamic torsion, or both, is common.

Wing leading edge notch

Open more at the middle leading edge of the swept-wing and delta-wing half spans, and the gap length is about 5% of the chord length (Figure 3b). Strong airflow at the notch at high angles of attack

The vortex changes the distribution of wing lift along the span, and also prevents the airflow separation of the wing tip.

Wing leading edge sawtooth

The chord of the outer wing extends about 10% forward, making the leading edge of the wing jagged (Figure 3c). It is mostly used for swept-back and triangular-thin wings, and functions similarly to a wing knife. On many thin wings with a sharp leading edge, the leading edge of the forward extension is appropriately rounded and angled down like the leading edge flap (leading edge droops). It can improve the airflow of the outer wing and improve the longitudinal stability of the wing at high angles of attack.

Wing cone twist

The leading edge portion of the wing gradually increases the range and angle of sagging from the wing root to the wing tip, so that the chord surface of the leading edge portion becomes a part of the cone surface (Figure 3d). Cone twist is mostly used in supersonic delta-wing aircraft. Conical torsion can delay airflow separation of sharp leading edge wings and tilt the leading edge suction forward, thereby reducing induced drag in flight (see Aerodynamic Characteristics).

Wing structure

Wing Introduction

The wing consists of a surface skin and an internal skeleton. The basic function of the wing structure is to form the streamlined shape of the wing, while transmitting the external load to the fuselage.

Wing

The wing structure should have sufficient strength, stiffness and life under external loads. Adequate stiffness refers to both the ability of the skin to maintain the shape of the airfoil under aerodynamic loads, and the ability of the wing to resist torsional and bending deformations.

Wing skin

It is an indispensable structural element that forms and maintains the shape of the wing. The cloth skin on the early aircraft only served to maintain the shape. The aerodynamic forces on the wings were transmitted to the wing skeleton through the tension of the cloth. As the aircraft's flight speed increased and aerodynamic loads increased, Mengbu was gradually eliminated because it was difficult to maintain its shape. After adopting metal aluminum skin, it began to be used as the main force member together with the skeleton, firstly used to transmit torque load. Because the skin is distributed along the wing profile, the torsional stiffness of the wing can be improved. Later, the aerodynamic load further increased, and the torsional stiffness of the wing was required to increase. The thickness of the skin was increasing. At the same time, the stringer was used to increase the stiffness of the skin. Therefore, the skin played an increasing role in bearing the wing bending moment .

Wing longitudinal skeleton

Refers to the components arranged along the wingspan, including spar, longitudinal wall and stringer. On the cloth wing, the spar is the only component that can withstand the bending moment. The spar has upper and lower edge strips and a web (the web is replaced by pillars and diagonal pillars in the truss beam). The upper and lower edge strips are subjected to bending moment loads in a tensile and compression manner. If the wing is subjected to an upward bending moment, the upper edge strip is compressed and the lower edge strip is tensioned. Tensile and compressive stresses (normal axial stresses) in the edge strips form a force couple that balances the moment load. The web transmits shear forces in a sheared manner. The longitudinal wall is similar in structure to the spar, but the edge is much thinner. It is arranged near the front and rear edges to transmit shear loads and increase the torsional stiffness of the wing. Beams are profiles that are connected to the inner surface of the skin along the span (its section has angles, T-shapes, Z-shapes, and cymbals, etc.). The stringer can increase the stiffness of the skin to withstand local aerodynamic loads, provide support when the skin is sheared, and together with the skin form the main load-bearing member for bending.

Wing transverse skeleton

It refers to the chordwise member of the wing, which is composed of ordinary ribs and reinforcing ribs. The role of common ribs

It is to maintain the profile of the wing and transmit the aerodynamic load from the skin to the web in the form of shear flow. The function of strengthening the ribs is to disperse and transfer the concentrated forces from the ailerons, flaps, and landing gear joints to the spar, longitudinal wall, and skin and other components.

The wing is divided into a beam wing and a monolithic wing according to the main bending structural elements.

Wing beam wing

A wing that receives most or all of the moment load from a spar. Its structural features are thick spar flanges, some of which are made of high-strength alloy steel, thinner skins, fewer or no beams. According to the number of spar, it can be divided into single-beam, double-beam and multi-beam wing (Figure 7). Beam wing is widely used in light aircraft. Wing

Wing monolithic wing

The thicker skin and stringer form the upper and lower wall panels of the wing. The wall panels are subjected to bending moment loads in the direction of tension and compression in the spanwise direction. The front and rear spar are relatively weak. The leading and trailing edges of the wing are equipped with movable wing surfaces such as leading edge flaps, trailing edge flaps, and ailerons, so the monolithic wing is a forced upper and lower wall plate only in the central part between the front and rear beams, forming a The wing box is called a box beam (Figure 7).

Supersonic fighters often use thin wings with small aspect ratios. Due to the small thickness of the wing and the large aerodynamic load, in order to ensure a certain torsional stiffness, thick skins are needed to connect the upper and lower stringers into one to form a multi-beam (or multi-web) structure wing. This wing can eliminate common ribs. On the triangular wing, due to the large chord dimension, similar multi-beam structures are also used.

Wing wing model

Icon:

Main operating surface on the wing

Control surfaces and attachments on the wing

Wing tip winglet

The above figure shows 1 position.

The vertical wing blade installed on the wing tip is mainly used to reduce the effect of the airflow around the lower surface of the wing tip to the upper surface, reduce the loss of lift, and improve the performance of the wing.

Aileron

2 positions shown above: low speed aileron.

3 position shown above: high speed aileron

The movable airfoil is usually installed outside the trailing edge of the wing to control the roll attitude of the aircraft. Some high-speed aircraft are also equipped with inboard ailerons to reduce twisting of the wings caused by aileron deflection.

Wing flap

4 positions shown above: flap slide fairing

5 positions shown above: leading edge flaps-Kruger flaps

The movable airfoil installed at the leading edge or trailing edge of the wing is used to increase the wing area and camber, increase the lift coefficient of the wing, and increase the lift. The flaps are mostly installed at the trailing edge of the wing, and the flaps installed at the leading edge are called the leading edge flaps.

Wing leading edge

6 position shown above: leading edge slats

A gap with the main body of the wing during normal operation allows part of the air on the lower surface of the wing to flow through the upper surface, thereby delaying the occurrence of airflow separation and increasing the critical angle of attack of the wing.

Aileron

7 position shown above: inside flap

8 position shown above: Outer flap

The active airfoil inside the trailing edge of the wing is common in large aircraft. It functions the same as the aileron during cruise flight to reduce the aerodynamic impact of the aileron, reduce the roll control effect, and interact with the flaps at low speeds.

Wing spoiler

9 position shown above: spoiler

10 position shown above: spoiler-speed reducer

A slab mounted on the upper surface of the wing that can be manipulated to open, which can be used to reduce lift, increase drag and enhance roll control. When the spoilers of the wings on both sides are opened symmetrically, the role at this time is mainly to increase resistance and reduce lift, so as to achieve the purpose of reducing speed and height, so it is also called a retarder; and when it is asymmetric When opened (usually caused by the pilot s roll maneuver), the lift of the wings on both sides is then asymmetric, which greatly increases the effectiveness of the roll maneuver, thereby accelerating the aircraft's roll.

Trim: It is a device installed on the control surface that can move relative to the control surface. It is usually used to balance the aerodynamic moment acting on the control surface. When the moment equilibrium state is reached, the conventional control system will not feel the aerodynamic force from the corresponding control surface.

Note 1: The above wing is only a schematic diagram. On a specific model, the actual configuration, function, and name of components in each position may be different due to different design concepts.

Note 2: 7 and 8 in the figure reflect the three different working positions of the flaps, not the three-layer flaps.

Wing attachment

Wing Knife: A thin plate installed vertically on the upper surface of the wing and parallel to the fuselage direction. It is used to block the movement of airflow in the spanwise direction of the wing and prevent the entire wing from stalling simultaneously in the spanwise direction. Common in swept-wing aircraft.

Vortex generator: Generates vortices on the upper surface of the wing, delaying the occurrence of airflow separation.

Wing Lift Principle

The principle of wing lift is explained by Newton's third law and Bernoulli's law. For the airfoil shown in the figure, when the air current parallel to the chord direction (which is considered as incompressible flow) flows through the wing, the cross section of the flow tube becomes smaller due to the wing obstruction, resulting in the wing up and down The surface air velocity increases. However, because the curvature of the upper surface of the wing is greater than the curvature of the lower surface, according to Bernoulli's law, it can be known that the velocity of the airflow on the upper surface is generally higher than the velocity of the airflow on the lower surface. Static pressure acting on the lower surface. Due to the pressure difference between the upper and lower surfaces, the wing eventually receives an upward resultant force, that is, lift.

Of course, with the change of the relative angle of attack of the air wing, the air flow field around the airfoil will also change significantly. When the angle of attack of the wing increases, the airflow is washed down due to the airfoil's obstruction to the airflow, which causes the airflow stagnation point near the leading edge to move down relative to the leading edge, resulting in a more pronounced lift effect. When the angle of attack of the wing is reduced or even negative, the effect of the airfoil camber will be weakened, that is, the lift will be reduced until a negative lift is generated.