Aerofoil - Definition, Terminology and Types

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.

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:

Where,

cl : lift coefficient

L: lift force

S: relevant surface

q: fluid dynamic pressure

⍴: fluid density

u: flow speed