Aerofoil - Definition, Terminology and Types

Edited By Vishal kumar | Updated on Jul 02, 2025 05:31 PM IST

A cross-sectional form called an aerofoil or airfoil is created with a curved surface, giving it the best lift-to-drag ratio possible during the flight. Drag is the component parallel to the direction of motion, and lift is the component where the force is perpendicular to the direction of motion. When using water as the working fluid, hydrofoils are designed using a similar concept. Aerofoils are extremely effective lifting forms because they produce greater lift than flat plates of the same area but are smaller in size while producing lift with substantially less drag.

This Story also Contains

Aerofoil Terminology
Chord
Melodic Line
The Top Surface
Lower level
Centre For Aerodynamics
The Point Of Pressure
The Attack’s Stance
Pitching Situation
How An Airfoil Shape Produces Lift
Types Of Aerofoil
Asymmetrical Aerofoil
Non-symmetrical aerofoil
What Is Lift?
How Does Aerofoil Produce Lift
Lift Coefficient

Aerofoil - Definition, Terminology and Types

The aerofoil's design is influenced by the aerodynamic properties, which in turn depend on the weight, speed, and use of the aircraft. These depend on particular words that must be defined in order to comprehend the design.

Aerofoil was initially created by German mathematician Max Munk and then improved upon in the 1920s by British aerodynamicist Hermann Glauert and others.

An aerofoil, or airfoil in American English (British English)

Aerofoil Terminology

The words linked to aerofoils are listed below:

Chord

A chord is defined as the distance along the chord line between the leading edge, which is the point on the aerofoil that has the most curvature, and the trailing edge, which is the point on the aerofoil that has the least curvature.

Melodic Line

The line that connects the leading and trailing edges is referred to as a chord line.

The Top Surface

The suction surface is another name for the top surface, which is connected to high velocity and low static pressure.

Lower level

The pressure surface with higher static pressure is often referred to as the lower surface.

Centre For Aerodynamics

At this centre, the pitching moment is unaffected by the lift coefficient and angle of attack (AOA).

The Point Of Pressure

In this centre, there is no pitching moment.

The Attack’s Stance

This is the angle made by an object's reference line and the incoming flow.

Pitching Situation

The aerodynamic force on the aerofoil was created by the moment or torque.

How An Airfoil Shape Produces Lift

What causes lift when an airfoil shape is used? When the top and bottom of an aeroplane's wings are identical, air will flow over each section at the same speed. However, an airfoil form enables air to pass over an aeroplane's upper wings more slowly than its bottom wings. The wings will then generate additional lift as a result.

An airfoil shape has a flat bottom and a curved top, as was already described. Air will move over an aeroplane's top section of wings more quickly than the bottom section due to its curvature. After all, the curved airfoil shape accelerates air by guiding it downward. Due to this design, air will pass over the top section of the structure more quickly than the bottom section. An aeroplane can produce more lift when the air travels over the top and bottom portions of its wings at different speeds.

Types Of Aerofoil

Asymmetrical and non-symmetrical aerofoils are the two categories into which aerofoils fall.

Asymmetrical Aerofoil

Since the chord line and mean camber line are identical on both the upper and lower surfaces, there is no lift at zero AOA. The majority of light helicopters employ them in their main rotor blades.

Non-symmetrical aerofoil

A cambered aerofoil is another name for it. The chord line is positioned above with a significant curvature due to the varied upper and lower surfaces of this. These have various camber lines and chord lines. The lift-to-drag ratio and stall characteristics of non-symmetrical aerofoils are better, and usable lift is produced at zero AOA. The drawbacks are that they are not economical and that unwanted torque is produced.

What Is Lift?

Lift is the force that holds an aeroplane in the air while directly opposing the weight of the aircraft. Every section of the aeroplane produces lift, but the wings produce the majority of the lift on a typical airliner. Lift is a mechanical aerodynamic force that an aeroplane experiences as it travels through the air. The lift has both a magnitude and a direction because it is a force, making it a vector quantity. The direction of lift is perpendicular to the flow direction and acts through the object's centre of pressure. Numerous factors affect how much lift there is.

How Does Aerofoil Produce Lift

By applying a downward push to the air as it passes, an airfoil creates lift. Newton's third law states that the air must pull on the elevated airfoil with an equal and opposite (upward) force. As it passes over the aerofoil, the wind changes course and takes a downwardly curving path.

Aerofoils are utilised in the design of aeroplanes, propellers, rotor blades, wind turbines, and other aeronautical engineering applications. In aeroplanes, the lift is the force that is generated by forward motion and opposes the weight of the aircraft. The above and below of the wing must split apart when the air passes over them. The increased flow of air under the wing, which is forced downward and forces the plane up, producing lift, is made possible by the wing's upward inclination and curved surface. This indicates that the force pulling the wing up is stronger, enabling the plane to fly.

Lift Coefficient

A dimensionless coefficient known as the lift coefficient tells us how the lift, fluid velocity, and associated reference area are related. Furthermore, a body is raised to fluid density in order to provide the lift. Additionally, the lift coefficient is mathematically represented as follows: 1707715726623

Where,

cl : lift coefficient

L: lift force

S: relevant surface

q: fluid dynamic pressure

⍴: fluid density

u: flow speed

Frequently Asked Questions (FAQs)

1. What is aerofoil?

The cross-sectional shape known as an aerofoil or airfoil is created with a curved surface, providing it with the best lift-to-drag ratio possible during the flight.

2. Who created the aerofoil?

Aerofoil was initially created by German mathematician Max Munk and then improved upon in the 1920s by British aerodynamicist Hermann Glauert and others.

3. What merits do aerofoil shapes have?

Aerofoils are extremely effective lifting forms because they produce greater lift than flat plates of the same area but smaller size while producing lift with substantially less drag.

4. How does an aerofoil produce lift?

By applying a downward push to the air as it passes, an airfoil creates lift.

5. Are aerofoils utilised anywhere?

Aerofoils are used in the design of aeroplanes, propellers, rotor blades, wind turbines, and other aeronautical engineering applications.

6. What airfoil form is the most effective?

The airfoil with the concave or "scooped out" lower surface is the most effective at producing the most lift.

7. What is the difference between a symmetrical and an asymmetrical aerofoil?

A symmetrical aerofoil has identical upper and lower surfaces, while an asymmetrical aerofoil has different curvatures on top and bottom. Symmetrical aerofoils produce zero lift at zero angle of attack and are often used in aerobatic aircraft for their predictable behavior when inverted. Asymmetrical aerofoils generate lift even at zero angle of attack and are more common in general aviation and commercial aircraft.

8. How do variable-geometry wings modify aerofoil characteristics?

Variable-geometry wings, also known as swing wings, can change their sweep angle during flight. This allows an aircraft to optimize its wing configuration for different flight regimes. At low speeds, the wings can be extended perpendicular to the fuselage, providing maximum lift and stability. For high-speed flight, the wings can be swept back to reduce drag and delay the onset of shock waves. This adaptability allows for improved performance across a wide range of flight conditions, though at the cost of increased complexity and weight.

9. What is the purpose of winglets on aircraft wings?

Winglets are vertical or angled extensions at the wingtips of aircraft. Their primary purpose is to reduce induced drag by disrupting the formation of wingtip vortices. By weakening these vortices, winglets improve the wing's efficiency, resulting in reduced fuel consumption and increased range. They also provide a small amount of additional lift and can improve the aircraft's stability and handling characteristics.

10. What is the chord of an aerofoil?

The chord of an aerofoil is the imaginary straight line connecting the leading edge (front) to the trailing edge (rear) of the aerofoil. It is used as a reference line for measuring various aerofoil characteristics, such as the angle of attack and camber. The chord length is an important parameter in calculating the aspect ratio of a wing.

11. What is the significance of the aerofoil's pressure distribution?

The pressure distribution around an aerofoil is crucial in determining its lift and drag characteristics. It shows how air pressure varies along the upper and lower surfaces. The difference in pressure between these surfaces generates lift. Understanding the pressure distribution helps in optimizing aerofoil design, predicting performance, and identifying potential areas of flow separation or shock formation. It's also essential in calculating the center of pressure and aerodynamic moments acting on the aerofoil.

12. What is the role of the aerofoil's trailing edge in lift generation?

The trailing edge of an aerofoil plays a crucial role in lift generation and overall aerodynamic performance. It's where the airflow from the upper and lower surfaces reunites. The shape and condition of the trailing edge affect the pressure recovery and the point of flow separation. A sharp trailing edge generally promotes smooth flow separation, while a blunt trailing edge can cause earlier separation and increased drag. The design of the trailing edge also influences the effectiveness of control surfaces like ailerons and flaps.

13. How do leading-edge devices like slats and slots work?

Leading-edge devices such as slats and slots are used to improve an aerofoil's performance at high angles of attack. Slats are movable surfaces that extend forward from the wing's leading edge, creating a gap. Slots are fixed openings near the leading edge. Both devices allow high-pressure air from below the wing to flow over the upper surface, energizing the boundary layer. This helps maintain smooth airflow at higher angles of attack, delaying stall and increasing the maximum lift coefficient.

14. How do vortex generators improve aerofoil performance?

Vortex generators are small, fin-like devices attached to the upper surface of an aerofoil. They create small vortices that energize the boundary layer, the thin layer of air closest to the surface. This energized boundary layer is better able to resist flow separation, allowing the aerofoil to maintain lift at higher angles of attack. Vortex generators can effectively delay stall and improve the aerofoil's performance, especially at low speeds or high angles of attack.

15. What is the purpose of a boundary layer fence on a wing?

A boundary layer fence is a thin plate or strip attached vertically to the upper surface of a wing, usually running from the leading edge towards the trailing edge. Its primary purpose is to prevent spanwise airflow along the wing, which can lead to early flow separation and loss of lift, especially on swept wings. By maintaining more uniform airflow over the wing, boundary layer fences help improve stall characteristics and overall aerodynamic performance, particularly at high angles of attack.

16. What is an aerofoil and how does it work?

An aerofoil, also known as an airfoil, is a specially shaped surface designed to generate lift when moving through air. It works by creating a difference in air pressure between its upper and lower surfaces. The curved upper surface causes air to move faster, creating lower pressure, while the flatter bottom surface creates higher pressure. This pressure difference results in an upward force called lift, which allows aircraft to fly.

17. Why is the shape of an aerofoil important?

The shape of an aerofoil is crucial because it determines how effectively it generates lift. The curved upper surface and flatter lower surface create a pressure difference that produces lift. The specific curvature, thickness, and angle of attack all affect the aerofoil's performance in different flight conditions.

18. What is the angle of attack in relation to an aerofoil?

The angle of attack is the angle between the chord line of an aerofoil (an imaginary line connecting the leading edge to the trailing edge) and the direction of the oncoming airflow. As the angle of attack increases, lift generally increases up to a certain point, after which the airflow separates from the upper surface, causing a stall.

19. What is the stagnation point on an aerofoil?

The stagnation point is the location on an aerofoil where the airflow splits, with some air moving over the upper surface and some moving under the lower surface. At this point, the air velocity relative to the aerofoil is zero, and the static pressure is at its maximum. The position of the stagnation point changes with the angle of attack, moving forward on the lower surface as the angle increases.

20. How does the Coandă effect contribute to lift generation?

The Coandă effect is the tendency of a fluid jet to stay attached to a convex surface. In the context of aerofoils, it helps explain why the airflow follows the curved upper surface of the wing. This effect enhances the pressure difference between the upper and lower surfaces, contributing to lift generation. The Coandă effect is particularly important in the design of high-lift devices and in understanding airflow behavior around curved surfaces.

21. How does camber affect an aerofoil's performance?

Camber refers to the asymmetry between the top and bottom surfaces of an aerofoil. A highly cambered aerofoil (more curved on top) generally produces more lift at lower speeds but also creates more drag. Less cambered aerofoils are more efficient at higher speeds. The amount of camber affects the lift coefficient and the angle at which the aerofoil stalls.

22. How does the thickness of an aerofoil affect its performance?

The thickness of an aerofoil affects its lift and drag characteristics. Thicker aerofoils generally produce more lift at lower speeds and have a higher maximum lift coefficient. However, they also create more drag, especially at higher speeds. Thinner aerofoils are more efficient at high speeds but may have poorer low-speed performance and stall more abruptly.

23. What is induced drag and how is it related to aerofoils?

Induced drag is a type of drag that occurs as a byproduct of lift generation by an aerofoil. It results from the wingtip vortices created by the pressure difference between the upper and lower surfaces of the wing. Induced drag increases as the angle of attack increases and is inversely proportional to the aspect ratio of the wing. It is a significant factor in determining the overall efficiency of an aircraft.

24. How do flaps and slats modify the performance of an aerofoil?

Flaps and slats are movable surfaces that modify the shape and effective camber of an aerofoil. Flaps, located at the trailing edge, increase the wing's camber and surface area when extended, generating more lift at lower speeds. Slats, found at the leading edge, help maintain smooth airflow over the wing at high angles of attack, delaying stall. Both devices allow aircraft to operate safely at lower speeds during takeoff and landing.

25. How does the aspect ratio of a wing affect its performance?

The aspect ratio is the ratio of a wing's span (length) to its average chord. Wings with higher aspect ratios (long and narrow) generally produce less induced drag and are more efficient for long-distance flight. Lower aspect ratio wings (short and wide) provide better maneuverability and are often used in fighter aircraft. The aspect ratio affects the wing's lift-to-drag ratio and stall characteristics.

26. What is the mean camber line of an aerofoil?

The mean camber line is an imaginary line that runs from the leading edge to the trailing edge of an aerofoil, equidistant from the upper and lower surfaces. It represents the average curvature of the aerofoil. The shape of the mean camber line significantly influences the lift characteristics of the aerofoil, with a more curved line generally producing higher lift coefficients at lower angles of attack.

27. What is the concept of supercritical aerofoils?

Supercritical aerofoils are designed to delay the onset of shock wave formation at high subsonic speeds. They typically have a flatter upper surface and a more pronounced curvature on the lower surface compared to conventional aerofoils. This design allows for higher cruise speeds and improved efficiency by reducing wave drag. Supercritical aerofoils are commonly used in modern commercial and military aircraft operating in the high subsonic regime.

28. What is the principle behind adaptive or morphing aerofoils?

Adaptive or morphing aerofoils can change their shape during flight to optimize performance for different conditions. This concept aims to combine the benefits of different aerofoil shapes into

29. What is the concept of aeroelasticity and how does it affect aerofoil design?

Aeroelasticity is the study of the interaction between aerodynamic forces and the elastic structure of an aircraft. As an aerofoil generates lift, it also experiences deformation due to these forces. This deformation can, in turn, alter the aerodynamic characteristics of the aerofoil. Phenomena like flutter, divergence, and buffeting are aeroelastic effects that can be dangerous if not properly accounted for. Aerofoil and wing design must consider these effects to ensure structural integrity and maintain desired aerodynamic performance across all flight conditions.

30. What is the significance of the critical angle of attack?

The critical angle of attack is the angle at which the lift coefficient reaches its maximum value before decreasing. Beyond this angle, the airflow begins to separate from the upper surface of the aerofoil, leading to a stall. Understanding the critical angle of attack is crucial for pilots and aircraft designers, as it determines the stall speed and affects the aircraft's maneuverability and safety margins.

31. How do active flow control techniques enhance aerofoil performance?

Active flow control techniques involve using energy input to modify the airflow around an aerofoil. These can include methods like boundary layer suction, blowing, plasma actuators, or synthetic jets. The goal is to delay flow separation, reduce drag, or increase lift, especially at high angles of attack. Active flow control can potentially allow for simpler mechanical systems by reducing the need for complex flaps or slats. However, these systems often require additional power and complexity, which must be balanced against their aerodynamic benefits.

32. What is the significance of the aerofoil's center of pressure?

The center of pressure is the point along the chord of an aerofoil where the total sum of the aerodynamic forces can be considered to act. Its position is crucial for aircraft stability and control. As the angle of attack changes, the center of pressure typically moves forward on most aerofoils. This movement affects the pitching moment of the wing and the overall balance of the aircraft. Understanding the center of pressure's behavior is essential for designing stable aircraft and determining control surface requirements.

33. How does surface roughness affect aerofoil performance?

Surface roughness on an aerofoil can significantly impact its performance. A rough surface increases skin friction drag and can cause premature transition of the boundary layer from laminar to turbulent flow. This typically results in increased drag and can affect the point of flow separation. However, in some cases, controlled roughness (like vortex generators) can be beneficial by energizing the boundary layer and delaying separation. Maintaining a smooth surface is generally crucial for optimal aerofoil performance, especially in high-performance aircraft.

34. How does the concept of circulation relate to lift generation in aerofoils?

Circulation in aerodynamics refers to the rotation of air around the aerofoil. According to the Kutta-Joukowski theorem, lift is directly proportional to the circulation around an aerofoil. As an aerofoil moves through the air, it creates a circulatory flow that adds to the freestream velocity above the wing and subtracts from it below. This circulation is responsible for the pressure difference that generates lift. Understanding circulation is crucial for analyzing lift production and forms the basis for many theoretical approaches to aerofoil design and analysis.

35. What is the concept of laminar flow aerofoils?

Laminar flow aerofoils are designed to maintain laminar (smooth, layered) airflow over a larger portion of their surface compared to conventional aerofoils. This is achieved through careful shaping of the aerofoil to create a favorable pressure gradient. Laminar flow reduces skin friction drag, potentially leading to significant improvements in efficiency. However, laminar flow aerofoils are more sensitive to surface imperfections and environmental conditions, and they may have different stall characteristics compared to traditional designs.

36. How does compressibility affect aerofoil performance at high speeds?

As an aircraft approaches the speed of sound, air compressibility becomes significant. This leads to the formation of shock waves, which can cause a dramatic increase in drag and a loss of lift. Compressibility effects can also shift the center of pressure rearward, potentially causing control issues. To mitigate these effects, high-speed aircraft use specially designed aerofoils, swept wings, and other features to delay the onset of shock waves and maintain efficiency in transonic and supersonic regimes.

37. How do canard configurations affect overall aircraft aerodynamics?

In a canard configuration, a small forewing is placed ahead of the main wing. This arrangement can offer several aerodynamic advantages. The canard generates lift, contributing to the aircraft's overall lift and potentially improving efficiency. It can also act as a pitch control surface, potentially eliminating the need for a traditional horizontal stabilizer. Canards can be designed to stall before the main wing, providing a natural stall warning and maintaining controllability. However, they also introduce complexities in terms of interference effects and overall aircraft balance.

38. How does wing sweep affect aerofoil performance?

Wing sweep, the backward angle of a wing relative to its root, is primarily used to delay the onset of shock waves in transonic and supersonic flight. Swept wings effectively reduce the component of airflow perpendicular to the leading edge, lowering the effective air speed over the wing. This allows aircraft to fly at higher speeds before experiencing compressibility effects. However, swept wings also introduce complexities in low-speed handling and stall characteristics.

39. What is the purpose of gurney flaps on aerofoils?

A Gurney flap is a small vertical projection attached to the trailing edge of an aerofoil. Despite its simple design, it can significantly enhance lift with only a modest increase in drag. The Gurney flap works by increasing the effective camber of the aerofoil and creating a region of separated flow behind it, which helps to increase the pressure difference between the upper and lower surfaces. It's particularly effective in improving the performance of thick aerofoils and is commonly used in racing cars and some aircraft designs.

40. How does Reynolds number affect aerofoil performance?

The Reynolds number is a dimensionless quantity that describes the ratio of inertial forces to viscous forces in a fluid flow. It affects how air behaves around an aerofoil. At low Reynolds numbers (typically associated with small or slow-moving objects), viscous forces dominate, and the airflow tends to be laminar. At higher Reynolds numbers, inertial forces dominate, leading to turbulent flow. The Reynolds number influences the aerofoil's lift and drag characteristics, as well as the point at which flow separation occurs.

41. How do winglets compare to other drag reduction devices?

Winglets are vertical or angled extensions at the wingtips designed to reduce induced drag. Compared to other drag reduction devices like wing fences or vortex generators, winglets are particularly effective at improving efficiency during cruise flight. They work by disrupting the formation of wingtip vortices, which are a major source of induced drag. While other devices may be more effective in specific flight regimes (e.g., vortex generators for high-lift situations), winglets offer a good balance of drag reduction across a wide range of flight conditions with relatively low weight penalty.