Dancing With The Wind: Unveiling The Ethereal Symphony Of Aerodynamics (Part I: Airfoils, Parts of an airfoil, Pressure Distribution)

17 min readJun 24, 2023

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The secret of flight does not lie in ambiguity anymore; in fact, the mysteries of flight were unraveled just about 100 years ago, then why do we still want to talk about the fundamentals of flight? Shouldn’t we move on? Well, a firm grip on the basics never hurts so here’s to learning the basics of flight! And there is no other way to do so without understanding the basic principles of aerodynamics. It’s what the entire aviation industry is based on, so let me explain the tenets of aerodynamics in a way that’ll resonate with anyone who’s willing to delve deep into this sector. Let’s begin.

LIFT: How airplanes fly

We’ve all been there. Our airplane lines up on the runway as it begins to venture on a journey to its destination. Maybe you’re anxious, excited, scared, tired, frustrated, or all of these emotions when the airplane’s taking off; personally, I have always found amusement in the notion of how this heavy metal tube with 2 wings can supposedly fly into the air without much of an issue?

As I saw the airplane slowly take off (“rotate” in a pilot’s terms), I’d always wonder what those wings would do, they’re not flapping like in the case of any bird, it puzzled me until I found the real answer to the question.

To start off, the airplane’s wing isn’t what you may think! The traditional worldview of a wing would encompass the wing being flat and rigid, whereas it is quite the opposite. The shape of a modern aircraft’s wing is known as the airfoil. It has a flat bottom and a curved surface at the top.

This particular shape of the wing optimizes the force of lift and minimizes the force of drag. What are those two things? When an object moves through a stationary fluid (air in this case), the fluid (air) exerts a force on the object, this force has an x-component and a y-component: The x-component in an aerodynamical context is referred to as DRAG, and the y-component is referred to as LIFT.

Different parts of airfoils and their functioning

The airfoil of a particular aircraft can vary greatly because of the sheer variety of aircraft being used in today’s world. For example, an aircraft designed to go supersonic will have a completely different airfoil structure than a bush plane. Nevertheless, all airfoils have a few key non-negotiables:

The Leading Edge

The forward edge of an airfoil refers to the “leading edge” of the airfoil. As the first point of contact with the oncoming airflow, the leading edge plays a critical role in determining the aerodynamic behavior and performance of the airfoil. It sets the stage for the complex dance between the airfoil and the surrounding air, dictating the flow patterns, lift generation, and overall efficiency of the aircraft or object to which it is attached.

The leading edge’s shape and configuration are carefully designed to optimize the airfoil’s performance characteristics. The choice of leading-edge shape depends on a multitude of factors, including the intended application, desired aerodynamic properties, and specific design objectives. Engineers employ a variety of leading-edge profiles, ranging from rounded to sharp or even blunted, each offering unique advantages in different scenarios.

A rounded leading edge, for instance, fosters smooth airflow over the airfoil surface. By gently curving the front edge, the airflow smoothly transitions from the undisturbed free stream to the airfoil’s surface, reducing turbulence and minimizing drag. This configuration is commonly found in applications where streamlined flow and reduced resistance are paramount, such as in high-speed aircraft or streamlined vehicles.

On the other hand, a sharp leading edge creates a more abrupt boundary between the airfoil and the oncoming airflow. This design choice can be advantageous in situations that require enhanced maneuverability and responsiveness. The sharp leading edge allows for rapid changes in direction and precise control, making it suitable for aircraft used in acrobatic maneuvers or scenarios that demand exceptional agility.

In certain specialized cases, a blunted leading edge may be employed. By slightly flattening the leading edge, engineers can manipulate the airflow behavior and modify the airfoil’s aerodynamic performance. This configuration can affect lift generation, stall characteristics, and overall stability. Blunted leading edges are often utilized in unconventional airfoil designs or specific applications where unique aerodynamic properties are desired.

Ultimately, the leading edge acts as the gateway to the aerodynamic world, determining how the air interacts with the airfoil and shaping the ensuing forces that enable flight. Whether it’s the graceful sweep of a bird’s wing, the precision of a high-performance aircraft, or the efficiency of a wind turbine blade, the leading edge stands as the pioneer, paving the way for remarkable advancements in aerodynamic design. Its careful shaping and configuration reflect the tireless efforts of engineers and scientists who strive to push the boundaries of flight, harness the power of the air, and unlock new frontiers of aerodynamic performance.

2. Trailing Edge

The trailing edge is the latter part of the airfoil structure. It represents the final boundary where the airflow meets the rear portion of the airfoil before it continues its journey downstream. While the leading edge initiates the interaction between the airfoil and the oncoming airflow, the trailing edge concludes this interaction, shaping the resulting aerodynamic forces and characteristics.

In terms of physical appearance, the trailing edge can have different configurations depending on the specific design requirements and intended application of the airfoil. It can be sharp, forming a thin and pointed edge, or it can be rounded, creating a smoother and more gradual transition. The chosen shape of the trailing edge influences the airflow behavior as it separates from the airfoil surface.

One significant aspect of the trailing edge is its impact on the generation of vortices. As the airflow reaches the trailing edge, a phenomenon known as “vortex shedding” occurs. Vortices, or swirling currents of air, are formed as the high-pressure air from the lower surface meets the low-pressure air from the upper surface. These vortices trail behind the airfoil, contributing to the overall aerodynamic characteristics and performance.

The design of the trailing edge is crucial for managing these vortices and controlling their effects. By carefully shaping and optimizing the trailing edge, engineers can influence the strength, stability, and behavior of the vortices, thereby impacting the airfoil’s overall performance. This includes considerations for reducing drag, enhancing lift, minimizing turbulence, and mitigating any adverse effects, such as buffeting or noise generation.

Overall, while often overshadowed by the leading edge in terms of attention and focus, the trailing edge of an airfoil plays a vital role in shaping the complex interaction between the airfoil and the airflow. Its design and configuration impact the behavior of vortices and contribute to the overall aerodynamic performance of the airfoil. By understanding and optimizing the trailing edge, engineers can unlock new possibilities in aircraft design, efficiency, and control.

3. Chord Line and The Angle of Attack

The Chord Line or the Wing Chord is defined as the line connecting the leading edge and the trailing edge. This is the line that determines the Angle of Attack of a wing — one of the crucial concepts in aviation.

The Angle of Attack (AoA) refers to the angle between the Chord Line and the oncoming airflow. It is a key parameter that significantly influences an aircraft's aerodynamic behavior and performance. The AoA directly affects the lift and drag forces generated by the wing, as well as other aerodynamic characteristics.

By adjusting the Angle of Attack, pilots and engineers can control the airflow over the wing and, consequently, the lift generated. Increasing the Angle of Attack beyond a certain point can enhance lift production up to a specific limit. However, exceeding this limit can lead to an aerodynamic phenomenon known as a stall (in simple terms, the aircraft starts to fall), where the smooth airflow over the wing is disrupted and lift is drastically reduced.

The Chord Line provides a clear reference to measure and adjust the Angle of Attack during flight. By changing the pitch attitude or adjusting control surfaces such as elevators or flaps, pilots can modify the orientation of the wing relative to the oncoming airflow, consequently altering the Angle of Attack. This control over the Angle of Attack allows pilots to optimize lift, adjust the aircraft’s descent or climb rate, and perform various maneuvers with precision.

Understanding and managing the Angle of Attack is essential for maintaining safe and efficient flight operations. Pilots receive training to interpret and respond to changes in the Angle of Attack, particularly in critical situations such as takeoff, landing, or during adverse weather conditions.

Moreover, aircraft designers and engineers consider the Angle of Attack and the associated Chord Line when developing new aircraft or optimizing existing designs. Through careful analysis, they can refine airfoil shapes, wing geometries, and control surface configurations to achieve desired performance characteristics at various Angle-of-Attack-ranges. This comprehensive understanding of the Angle of Attack enables the creation of aircraft that are efficient, stable, and capable of performing a wide range of flight maneuvers.

4. Camber Line

If we draw a line between the top and bottom surface of an airfoil, we get the mean camber line. The Camber Line describes the curvature of an airfoil. For example, a symmetrical airfoil has 0 camber, as there is uniformity in the wing overall. In an asymmetrical scenario, the camber can either be positive or negative. Let’s explore the aforementioned in detail:

By analyzing the camber line, engineers can gain valuable information about lift distribution, pressure distribution, and the overall aerodynamic performance of the wing.

In the case of a symmetrical airfoil, the mean camber line coincides with the chord line, resulting in a camber of zero. This means that the upper and lower surfaces of the wing are mirror images of each other, exhibiting uniformity in the wing overall. Symmetrical airfoils are commonly used in applications where lift requirements are similar in both directions, such as in aerobatic aircraft or certain types of rotor blades.

On the other hand, in an asymmetrical airfoil, the mean camber line exhibits a non-zero curvature. This indicates that the upper and lower surfaces of the wing differ in their shape and curvature. Depending on the specific design, the camber can be positive or negative.

In a positively cambered airfoil, the mean camber line is curved such that the upper surface is more pronounced than the lower surface. This configuration promotes greater lift generation, making it suitable for applications that require enhanced lift characteristics, such as in most general aviation aircraft or low-speed flying scenarios.

Conversely, a negatively cambered airfoil exhibits a mean camber line that is curved in a way that the lower surface is more pronounced than the upper surface. This configuration can provide advantages in specific applications where reduced drag is desired, such as in high-speed aircraft or racing vehicles.

The selection of camber depends on a variety of factors, including the intended use of the airfoil, desired lift and drag characteristics, and performance requirements. Through careful design and analysis, engineers can optimize the camber line to achieve the desired aerodynamic properties and performance goals for a given airfoil design.

PRESSURE DISTRIBUTION

Although the airfoil shape does play a major role in determining the lift an aircraft wing experiences, it is the pressure distribution around the wing that really influences how efficiently an aircraft can generate lift. This is because during the flight, there are a variety of forces and stresses acting on the wing, but those stresses can be classified into 2broad categories: Wall Shear Stress and Pressure Stresses.

Wall Shear Stress

The Wall Shear Stress on aircraft wings acts tangentially to the surface of the wing. It is a result of the interaction between the air flowing over the wing and the wing’s surface. The wall shear stress is responsible for the transfer of momentum from the air to the wing, which generates lift and affects the overall aerodynamic performance of the aircraft.

The wall shear stress is highest near the leading edge of the wing and decreases towards the trailing edge. This variation in shear stress distribution is due to the difference in velocity between the boundary layer of air near the wing surface and the freestream air flowing over the wing. The boundary layer is a thin layer of air that forms on the wing’s surface as the air flows past it.

The wall shear stress can have significant effects on the performance and structural integrity of the wing. Excessive shear stress can lead to surface damage, such as erosion or fatigue, especially in regions of high-stress concentration. Therefore, engineers and designers must consider the wall shear stress when designing aircraft wings to ensure they can withstand the forces experienced during flight.

To calculate the wall shear stress, various mathematical models and empirical formulas are used, taking into account factors such as air density, wing geometry, and airflow conditions. Computational Fluid Dynamics (CFD) simulations are often employed to analyze and predict the distribution of wall shear stress along the wing’s surface.

Understanding and accurately predicting the wall shear stress is crucial in optimizing wing design for improved aerodynamic performance, fuel efficiency, and structural durability. By effectively managing the wall shear stress, aircraft designers can create wings that enhance lift generation, reduce drag, and ensure safe and efficient flight operations.

Pressure Stresses

Pressure stresses act perpendicularly to the surface of the wing and are another important aspect of the aerodynamic forces acting on aircraft wings. Unlike the wall shear stress, which acts tangentially to the wing surface, pressure stresses act perpendicularly to the wing surface.

Pressure stresses are a result of the variations in air pressure between the upper and lower surfaces of the wing. As the air flows over the wing, it experiences changes in velocity and pressure due to the wing’s shape and angle of attack. These pressure differences create a force that acts normal, or perpendicular, to the wing’s surface.

On the upper surface of the wing, where the airflow is faster, the air pressure is lower compared to the lower surface. This pressure difference generates an upward force known as lift. Lift is responsible for supporting the weight of the aircraft and keeping it airborne. The higher the pressure difference, the greater the lift generated.

Conversely, on the lower surface of the wing, the airflow is slower, resulting in higher air pressure. This higher pressure creates a downward force called the wing’s weight or gravity. The weight force counteracts the lift force, and the balance between these two forces determines the aircraft’s ability to maintain level flight or perform maneuvers.

In addition to lift and weight, pressure stresses also contribute to drag, which is the resistance encountered by the aircraft as it moves through the air. Pressure drag is caused by the difference in air pressure between the front and rear surfaces of the wing. The greater the pressure difference, the higher the pressure drag experienced.

To optimize the aerodynamic performance of aircraft wings, engineers consider various factors that influence pressure stresses. These factors include the wing’s shape, angle of attack, airspeed, and air density. Through careful design and analysis, engineers can create wings with favorable pressure distributions that maximize lift while minimizing drag.

Computational methods, such as Computational Fluid Dynamics (CFD), are commonly used to simulate and analyze the pressure distribution over the wing surface. These simulations provide valuable insights into the complex interactions between the air and the wing, aiding in the design process and performance optimization.

By understanding and managing pressure stresses, aircraft designers can enhance the lift-to-drag ratio, improve fuel efficiency, and ensure the structural integrity of the wings. Optimizing pressure distribution is a crucial aspect of wing design to achieve safe, efficient, and high-performance flight.

and are another important aspect of the aerodynamic forces acting on aircraft wings. Unlike the wall shear stress, which acts tangentially to the wing surface, pressure stresses act perpendicularly to the wing surface.