How Do Airplanes Fly? Physical Explanation of Lift Force
March 12, 2025 • ☕️ 4 min read • 🏷 aviation, airplanes
Translated by author into: English
Airplanes soaring through the sky, defying gravity, is a fascinating sight for most of us. So how do airplanes really fly? How is the lift force that keeps an airplane in the air created?
Most of us have learned in school or popular science resources that the air flowing over the wing of an airplane flows faster than the air flowing under it, and that airplanes rise due to the pressure difference according to Bernoulli’s principle. However, the situation is not that simple in reality.
In this article, we will examine the real physical structure of lift force through the comprehensive explanations of David Anderson and Scott Eberhardt.
(Prepared using the article “How Airplanes Fly: A Physical Description of Lift” by David Anderson and Scott Eberhardt.)
1. The Traditional Explanation of Flight and Its Problems
In many books and lectures, the basic principle of flight is stated as follows:
“The air passing over the top of the wing moves faster than the air passing under it. According to Bernoulli’s principle, as the speed increases, the pressure decreases. Thus, low pressure occurs at the top and high pressure at the bottom, and the airplane lifts off.”
However, according to Anderson and Eberhardt, this common explanation is incomplete and misleading. This explanation contains two major problems:
- Misinterpreted Bernoulli’s Principle: The longer the top of the wing, the faster the air is forced over the top. This is a simplification that does not fit the physical facts.
- Neglect of Newton’s Laws: The traditional explanation ignores the fact that the airflow pushes the wing down.
2. The Physical Basis of Lift Force: Newton’s Laws
Anderson and Eberhardt put forward Newton’s third law (Action-Reaction) as the fundamental physical principle in explaining lift force:
- The wing directs the air downward.
- In return, the air pushes the wing upward.
- This mutual interaction creates the lift force that allows the aircraft to rise.
In other words, the aircraft rises to the extent that it pushes the air downward. This principle actually explains why aircraft take off at a higher angle of attack. As the angle increases, the air is pushed downward more, which increases the lift force.
3. Is Bernoulli’s Principle Completely Wrong?
Bernoulli’s principle is a real law of physics that plays a role in lift. However, it is not enough to explain lift on its own. In fact, Bernoulli’s principle should be considered together with Newton’s third law.
- Air does indeed flow faster on the top of the wing. However, this speed difference is not due to the shape of the wing, but due to the tendency of the airflow to stick to the wing surface (Koanda effect).
- Thus, the air curves downward on the wing surface, creating a circulation. This creates a low-pressure region on the top. Bernoulli’s principle explains the low pressure created by this circulation.
As Anderson and Eberhardt also stated, lift is better understood through the combination of Bernoulli’s principle with Newtonian mechanics.
4. The Koanda Effect and the Role of Circulation
Many people may have heard of the Koanda effect for the first time. The Koanda effect is simply the tendency of fluids (including air) to stick to surfaces and move. This effect causes the airflow on the upper surface of the wing to stick to the wing and curve downward.
- This curvature and circulation means that the air is pushed down, and Newton’s third law comes into play.
- In addition, circulation represents the continuous airflow around the wing, creating the pressure differences that form the basis of lift.
5. Conclusion: How Should We Understand Lift?
As this blog post and Anderson and Eberhardt’s article show, to properly understand lift, we need a broader physical context, not just simple school explanations. Lift:
- Occurs according to Newton’s third law: Air down, airplane up.
- Bernoulli’s principle does not act alone, but in conjunction with the Koanda effect and circulation.
- Traditional explanations only provide a superficial idea and are often misleading.
Understanding the physics of flight based on these truths will help eliminate misinformation about aviation and provide a more solid scientific basis for learning.