What is Aerodynamics Lift?

Understanding the forces that act on objects moving through air is essential in aerodynamics and fluid mechanics. While lift force enables flight by creating an upward force, there are other important aerodynamic forces at work. Drag force, which opposes motion through air, is equally crucial for aircraft design and engineering applications. To get a complete picture of aerodynamic forces, we recommend reading our comprehensive guide on What is Drag in Aerodynamics, which explains how drag affects everything from airplane efficiency to sports performance.

Now, let’s dive explore aerodynamics lift – the force that makes flight possible.

Figure 1: Drag & lift forces applied on an airfoil

What is Aerodynamics Lift?

Aerodynamics lift is the force that acts perpendicular to the direction of fluid flow and enables objects to rise against gravity. Simply put, lift force pushes upward on wings, allowing airplanes to fly and birds to soar through the sky.

What is lift in aerodynamics? In technical terms, lift is generated when air flows over and under a curved surface (like an airfoil) at different speeds, creating a pressure difference. This pressure difference results in a net upward force – the lift force.

The lift force symbol is typically represented as L in equations, and it’s measured in Newtons (N) in the SI system. Understanding lift force definition physics is crucial for anyone working in aviation, aerospace engineering, or CFD analysis.

Key characteristics of lift force:

• Acts perpendicular to the direction of airflow
• Depends on wing design, angle of attack, and air properties
• Essential for aircraft design and flight mechanics
• Can be calculated using the lift force formula

What is lift in flight? During flight, lift force must balance the weight of the aircraft. When lift equals weight, the airplane maintains level flight. When lift exceeds weight, the aircraft climbs.

Figure 2: How aerodynamics lift is generated – air pressure differences above and below the wing create the upward lift force

The Lift Force Formula and Equation

To calculate lift force, engineers and physicists use a fundamental equation known as the lift force formula. This formula helps us understand the relationship between an object’s speed, its shape, and the air it moves through. It is the most important lift force equation in aerodynamics.

The main lift force formula in fluid mechanics is:

Let’s break down what each part of this lift force equation means in simple terms:

• L (Lift Force): This is the final lift force we want to calculate. It is the upward force acting on the wing, measured in Newtons (N).
• ρ (rho): This is the density of the air. Air density changes with altitude and temperature. Denser air can generate more lift force.
• V (Velocity): This is the speed of the object relative to the air. As the velocity increases, the lift force increases significantly (by the square of the velocity).
• S (Surface Area): This is the wing’s reference area. A larger wing area can generate more lift.
• C_L (Lift Coefficient): This is the coefficient of lift. It is a special number that describes how efficiently a wing’s shape (airfoil) generates lift. The lift coefficient is very important because it depends on the wing design and the angle of attack. It has no dimensions.

Understanding this lift force formula is the first step to mastering what is lift in aerodynamics. It provides a powerful tool for aircraft design and CFD analysis.

How is Lift Generated by a Wing?

Now that we know the lift force formula, let’s explore how is lift generated by a wing. The magic is in the special shape of a wing, known as an airfoil, and how it interacts with the air.

There are two main principles that help us understand this process: Bernoulli’s Principle and Newton’s Third Law. Both are correct and describe different parts of the same phenomenon.

Bernoulli’s Principle and Pressure Difference

An airfoil has a curved top surface and a flatter bottom surface.

• As air flows towards the wing, it splits to go over the top and under the bottom.
• Because the top surface is more curved, the air traveling over the top must move faster to meet the air from the bottom at the same time.
• According to Bernoulli’s principle, faster-moving air has lower pressure.
• This creates a pressure difference: high pressure under the wing and low pressure above the wing.

This pressure difference results in a net upward force, pushing the wing up. This force is the aerodynamics lift. It’s like a gentle but powerful push from below.

Figure 3: Illustration of how lift is generated by a wing, showing both Bernoulli’s Principle (pressure difference)

Newton’s Third Law and Action-Reaction

Another way to understand lift is by using Newton’s third law of motion.

• A wing is usually tilted slightly upwards, which is known as the angle of attack.- As the wing moves through the air, its shape and angle of attack push the air downwards. This is the “action.”
• Newton’s third law states that for every action, there is an equal and opposite reaction.- Therefore, as the wing pushes the air down, the air pushes the wing up. This “reaction” is the lift force.

In reality, both explanations are happening at the same time. The airfoil shape causes a pressure difference (Bernoulli) and also deflects air downwards (Newton), and together, they generate the powerful lift force needed for flight.

 

Factors Affecting Lift Force

The amount of aerodynamics lift a wing can generate is not constant. It changes based on several important conditions. Understanding these factors is key for pilots and for effective aircraft design. Let’s look at the main factors affecting lift force, which are all part of the lift force formula.

1. Angle of Attack

The angle of attack is the angle between the wing (the airfoil’s chord line) and the direction of the oncoming air. This is one of the most critical factors.

• A small increase in the angle of attack causes a large increase in the lift coefficient, which results in more lift force.
• However, this only works up to a certain point (usually around 15-20 degrees).
• If the angle of attack becomes too high, the airflow can no longer follow the wing’s curved surface and separates. This causes the lift to decrease suddenly, a dangerous condition known as a “stall.”
• Therefore, controlling the angle of attack is very important in aviation.

2. Wing Design and Shape (Airfoil)

The specific shape of the wing, known as the airfoil design, has a huge impact on lift.

• Camber: This is the curve of the airfoil. A wing with more curve (higher camber) is designed to produce more lift at lower speeds.
• Wing Area: As we saw in the lift force formula, a larger wing area (S) captures more air. This generates a greater lift force. This is why large, heavy cargo planes have very large wings.
• The overall wing design is always a balance to produce the maximum lift for the minimum drag.

Figure 4: Lift generated by symmetrical airfoil Vs. Cambered

3. Velocity (Speed)

Velocity is one of the most powerful factors in creating lift.

• The lift force formula shows that lift is proportional to the square of the velocity (V2).
• This means that if you double the speed of the aircraft, you will quadruple the lift force.
• This powerful relationship is why airplanes must reach a very high speed on the runway before they have enough lift to take off.

4. Air Density

Air density (ρ) refers to how many air molecules are packed into a certain volume.

• Lift force is directly proportional to air density. Denser air creates more lift.
• Air is denser at sea level and becomes less dense at higher altitudes.
• This is why an airplane needs a longer runway to take off from an airport at a high altitude; it must achieve a higher speed to compensate for the lower air density and generate enough lift.

 

How to Calculate Lift Force

Now that you understand the lift force formula and the factors that influence it, let’s learn how to calculate lift force with a simple, step-by-step example. This calculation is fundamental in aerodynamics and aircraft design.

The process involves finding the values for each variable in the lift force equation and then putting them together.### Step-by-Step Calculation Guide

1. Identify Your Variables: First, you need to know the values for air density (ρ), velocity (V), wing surface area (S), and the lift coefficient (C_L).
2. Find the Air Density (ρ): The density of air changes with altitude. For simple calculations, we often use the standard value at sea level, which is approximately 1.225 kg/m³.
3. Determine the Velocity (V): This is the speed of the aircraft in meters per second (m/s). For example, a small airplane might have a takeoff speed of 50 m/s.
4. Find the Wing Surface Area (S): This is the total area of the wings, measured in square meters (m²). You can usually find this in the aircraft’s specifications.
5. Determine the Lift Coefficient (C_L): This is the most complex value. The lift coefficient depends on the airfoil design and the angle of attack. For simple problems, this value is often given. In real-world engineering, it is found through wind tunnel testing or CFD analysis.

 

CFD Simulation of Aerodynamics Lift

While the lift force formula gives us a great theoretical understanding, modern aircraft design relies on powerful computer tools to get precise results. The most important tool for this is Computational Fluid Dynamics (CFD).

CFD simulation is a method where engineers use computers to model and analyze fluid flow. Instead of building physical prototypes for every new idea, engineers can create a virtual model and test it on a computer. This allows for detailed analysis of the aerodynamics lift on any shape, from a simple airfoil to a complete airplane.

Applications of CFD in aerodynamics are vast. Engineers use it to:

• Visualize complex airflow patterns around a wing.
• Accurately calculate the lift force and drag force for different wing designs.
• Optimize the angle of attack to achieve the highest lift coefficient.
• Test how an aircraft will behave at different speeds and altitudes.

Software like ANSYS Fluent is an industry standard for performing these complex simulations. By using CFD, companies can design safer, more efficient aircraft much faster than before. At CFDLand, we specialize in these advanced analyses. You can explore a wide range of practical examples and projects in our Aerodynamics & Aerospace CFD Simulation category. These projects show how CFD is used to solve real-world engineering challenges in aviation and aerospace.

Figure 5: Velocity contour and streamlines of fluid flow around the airfoil, adopted from “Suction Slot On 3D Airfoil CFD Simulation”

Click to access the Aerodynamics CFD Projects.

Conclusion

In this guide, we have explored the essential principles of aerodynamics lift. We learned that lift force is the upward push that allows airplanes to fly, acting perpendicular to the direction of airflow. We broke down the lift force formula, showing how velocity, wing design, angle of attack, and air density are the key factors in generating lift.

From the physics of airfoils explained by Bernoulli’s Principle to the power of modern CFD simulation in aircraft design, you now have a solid understanding of what is lift in aerodynamics. Mastering the concept of lift force is the first step toward understanding the complex and fascinating world of aviation and fluid dynamics. It is the fundamental force that has allowed humanity to conquer the skies.