Aerofoil

Aerofoil is also called an airfoil. It is a surface shaped like an airplane wing, tail, or propeller blade, that produces lift and drag when moved through the air. An aerofoil generates a lifting force that acts at right angles to the airstream and a dragging force that acts in the same direction as the airstream. High-speed aircraft mainly implement low-drag, low-lift airfoils that are thin and streamlined and on the other hand, slow aircraft that carry heavy loads use thicker airfoils with high drag and high lift. 

What is Aerofil?

Aerofoil refers to a cross-sectional shape having a design with a curved surface that provides the most favourable ratio between lift and drag in flight. Lift is the component that helps the force turn out to be perpendicular to the motion’s direction while drag is the component that is parallel to the motion’s direction.

Aerofoil or also known as Airfoil is a structure with curved surfaces designed to give the most favourable ratio of lift to drag in flight, which is mainly used as the basic form of the fins, wings, and tailplanes of most aircraft. Aerofoil is the cross-section design of the wing, blade, or sail. Lift is the component such that the force is perpendicular to the direction of motion and drag is the component parallel to the direction of motion. A similar idea is being used in the designing of hydrofoils which is used when water is used as the working fluid. A body that is airfoil-shaped, moving through a fluid produces an aerodynamic force. The design of the aerofoil depends on the weight, speed, and purpose of the aircraft and mainly depends on the aerodynamic characteristics. These are dependent on certain terms that need to be defined to understand the design.

Aerofoil Terminology

An aerofoil consists of various cross-sectional shapes. Different types of aerofoils are used for the construction of aircraft wings. To differentiate between different aerofoil shapes, an aerofoil’s properties are defined and specific terminologies are used. Aerofoil Terminology. An Aerofoil is being designed with a shape that has the capability of producing lift with relatively high efficiency as it passes through the air. An aerofoil can have many cross-sectional shapes. The terms which are related to aerofoils are as follows.

• Chord: Chord can be defined as the distance between the leading edge, at the front of the aerofoil that is the point, and has maximum curvature and the trailing edge, at the rear of the aerofoil, that is the point with a maximum curvature along the chord line. It is a distance between the leading and trailing edges measured along the chord line.

• Chord Line: Chord line is the straight line connecting the leading and trailing edges.

• Leading-Edge: It is an edged part of an aerofoil that hits the air particles first.

• Lower Surface: The lower surface is a higher static pressure surface which is also known as a pressure surface. It is the surface of an aerofoil between the leading and trailing edges, on the lower side.

• Mean Camber Line: It is a line joining the leading and trailing edges of an aerofoil, at an equal distance from the upper and lower surfaces.

• Maximum Camber: It is the maximum distance of the mean camber line from the chord line.

• Maximum Thickness: It is the maximum distance of the lower surface from the upper surface.

• Trailing Edge: It is an edged part from an aerofoil that hits the air particles last.

• Upper Surface: The upper surface is associated with high velocity and low static pressure, which is also known as suction surface. It is the surface of an aerofoil between the leading and trailing edges, on the upper side.

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When the aerofoil is moving through a fluid, the following are the terms used to describe the behaviour:

1. Aerodynamic Center: The centre where the pitching moment is independent of lift coefficient and angle of attack.

2. Center Of Pressure: The centre where the pitching moment is zero.

3. The Angle Of Attack (AOA): The angle of attack is formed between a reference line on a body and the oncoming flow.

4. Pitching Moment: The moment or torque produced on the aerofoil by the aerodynamic force is known as the Pitching moment.

Lift Coefficient

The lift coefficient is a relationship between the lift generated by a lifting body to fluid density, fluid velocity, and the associated reference area, this is a dimensionless coefficient. Mathematical representation is as follows:

C\[_{L}\] = \[\frac{L}{q_{s}}\] = \[\frac{L}{\frac{1}{2}p.u.u.s}\] = \[\frac{2L}{p.u.u.s}\]

Where,

C\[_{L}\] : lift coefficient

L: lift force

S: relevant surface

q: fluid dynamic pressure

ρ: fluid density

μ : flow speed

Types of Aerofoil 

The types of aerofoils that are used are as follows:

1. Symmetrical Aerofoil:

This has identical upper and lower surfaces that produce no life at zero AOA such that the chord line and mean camber line are the same. In most of the light helicopters in their main rotor blades, these applications are fine. It is the type of aerofoil that has identical upper and lower surfaces such that the chord line and mean camber line happen to be the same, resulting in the production of no life at zero angles of attack. Symmetrical aerofoil has application in the main rotor blades of various light helicopters.

2. Non-symmetrical Aerofoil:

Non-symmetrical aerofoil has different upper and lower surfaces such that the chord line is placed above with large curvature, and it is also known as a cambered aerofoil. This aerofoil is also known as cambered aerofoil and it has different upper and lower surfaces such that the chord line happens to be placed above with large curvature. The chord line and chamber line of Non-symmetrical aerofoil are different and the advantages of this type are a better lift to drag ratio and stall characteristics, thereby resulting in the production of a useful lift at zero angles of attack.

3. These have different chord lines and chamber lines. These are the advantages of a non-symmetrical aerofoil, that is the lift to drag ratio and stall characteristics are better and useful lift is produced at zero AOA. The only disadvantages are that they are not economical and there is a production of undesirable torque.

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Fun Facts

1. In American English it is Airfoil and in British English, it is known as Aerofoil.

2. An Aerofoil or Airfoil is the shape of a wing or blade of a propeller.

3. Aerofoil was invented by Sir George Cayley.

4. Aerofoil will provide either lift or downforce, when it is moving through a fluid, depending on what it is used for.

5. According to Newton’s third law, the air must exert equal and opposite force on the airfoil, which is known as lift.

6. Birds fly on the basis of airfoils for wing-lift.

7. The underwater fins of sailboats, such as centerboards, are also lifting foils and operate on the same principles as airfoils. Technically they should be called hydrofoils, but this term has already been taken; generally, they are just referred to as "foils"

It is important to note that any thin object such as a flat plate or even the deck of a bridge, at an angle of attack with respect to the airflow, will generate lift; there is nothing "magic" about the shape of an airfoil. However, the lift is generated with the minimum of drag, so it is important for efficiency, the airfoil shape ensures that.