Aerofoil : Introduction, Terminology, Types, Questions

An airfoil is another name for an aerofoil. It is a surface that creates lift and drag when moving through the air and is shaped like an aeroplane wing, tail, or propeller blade. An aerofoil produces a dragging force that moves in the same direction as the airstream and a lifting force that acts at right angles to the airstream. Aerofoils used by fast-moving aircraft are typically thin, streamlined designs with minimal drag and lift, whereas those used by slower-moving aircraft carrying heavy loads are thicker, more complex designs with high drag and lift.

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Key Terms: Aerofoil, Airfoil, lift, Chord, Camber, Aeroplane , Direction of motion

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Introduction to Aerofoil 

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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 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 smaller 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.

One of the most important aspects of aerodynamics is the design of aerofoils. Additionally, different aerofoils are advantageous for varied flying regimes. Most notably, symmetrical aerofoils may generate lift at zero angle of attack, even though they are better suited for frequent inverted flight like in an aerobatic aircraft.

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Aerofoil Terminology 

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These are numerous cross-sectional shapes that make up an aerofoil. Wings for aeroplanes are built using many types of aerofoils. An aerofoil’s attributes are described, and particular terminologies are used to distinguish between various aerofoil shapes. Terminology for aerofoils. An aerofoil is made with a shape that can produce lift while flying through the air with a comparatively high efficiency. Numerous cross-sectional shapes are possible for an aerofoil. The following are terminology that pertain to aerofoils.

• Chord 

The leading edge, located at the front of the aerofoil, is the point with the greatest curvature, and the trailing edge, located at the back of the aerofoil, is the point with the greatest curvature along the chord line. This distance is referred to as the chord. It is a measurement along the chord line between the leading and trailing edges.

• Chord line

The straight line connecting the leading and trailing edges are known as chord lines.

• Leading edge

The edged part of an aerofoil that hits the air particles first is known as the leading edge.

Aerofoil Terminology

• Trailing edge

The edged part of the aerofoil that hits the air particles last is known as trailing edge.

• Lower surface

The lower surface is also referred to as a pressure surface and has a higher static pressure. It is an aerofoil’s lower side surface located between the leading and trailing edges.

• Upper surface

High velocity and low static pressure are characteristics of the upper surface, also referred to as the suction surface. It is located on the upper side of an aerofoil, between the leading and trailing edges.

• Mean Camber line

The line joining the leading and trailing edges of an aerofoil that is equidistant from upper and lower surfaces is known as mean camber line.

• Maximum Camber

The maximum distance of the mean camber line from the chord line is referred to as maximum camber.

• Maximum thickness 

Maximum distance is the maximum possible distance between lower and upper surfaces.

• Pitching moment 

Pitching moment is the torque produced on the aerofoil due to an aerodynamic force.

• Centre of pressure 

The centre of pressure refers to the centre of aerofoil where the pitching moment is equal to zero.

• Angle of attack

When an oncoming flow hits the aerofoil, an angle of attack is formed between the line of oncoming flow and the reference line of the body.

• Aerodynamic centre

Aerodynamic centre is the centre of aerofoil where the pitching moment is found to be independent of angle of attack and lift coefficient.

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Lift Coefficient 

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

Aerofoil lift 

• 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.

The link between the lift produced by a lifting body and the fluid density, fluid velocity, and the related reference area is described by the lift coefficient, which is a dimensionless coefficient. The following is the mathematical representation:

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Types of Aerofoil

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There are basically two types of aerofoils. They are:

Types of Aerofoil

• Symmetrical Aerofoil 

The chord line and mean camber line of this are the same because it has identical upper and lower surfaces that produce no life at zero AOA. These applications work just fine in the main rotor blades of the majority of light helicopters. The chord line and mean camber line of this particular form of aerofoil are equal on the upper and lower surfaces, which results in the absence of life at zero angles of attack. The primary rotor blades of various light helicopters use symmetrical aerofoils.

• Non-symmetrical Aerofoil 

A non-symmetrical aerofoil, also referred to as a cambered aerofoil, has differing upper and bottom surfaces such that the chord line is positioned above with a significant curve. This aerofoil, also known as a cambered aerofoil, has various upper and lower surfaces, which causes the chord line to be positioned above and have a significant curve. Non-symmetrical aerofoils have varied chord lines and chamber lines, and their advantages include superior lift-to-drag ratios and stall characteristics, which produce effective lift at zero angles of attack. These have various chamber lines and chord progressions.

Useful lift is created at zero AOA, and the lift to drag ratio and stall characteristics are better. These are the benefits of a non-symmetrical aerofoil. The only drawbacks are that they are not inexpensive and that unwanted torque is produced.

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Things to remember 

• Centreboards, which are a type of underwater sailboat fin, are lifting foils that function similarly to aerofoils. 
• At an angle of attack with regard to the airflow, an object will produce lift. 
• The aerofoil form guarantees that the lift is produced with the least amount of drag possible, which is vital for efficiency.
• Depending on what it is used for, an aerofoil will provide either lift or downforce when it is travelling through a fluid.
• The two types of aerofoils are symmetrical and non-symmetrical aerofoil
• Aerofoils has significant applications in aeronautical engineering.