The Construction and Physics Behind Aircraft Wings
- Ji Sung Lee
- Feb 9, 2025
- 4 min read
Sometimes, when looking out the window during a flight, one may see the wings swinging up and down significantly when the aircraft is going through wind gusts. Anxious fliers often get distressed by this, worrying that the wing may snap off. However, many people are unaware of the fact that the swinging wings are the signal that the aircraft is modulating itself and that stiff wings are, in fact, much more dangerous. More than its flexibility, aircraft wings provide the fundamental force that allows the plane to glide up—the lift force. What allows plane wings to have such flexibility, and what are the underlying principles of a plane wing providing lift force?
How Plane Wings are Designed
Take the Boeing 787 as an example. The B787 Dreamliner is considered to be one of the most remarkable aircraft in terms of its wing flex. Wing flex refers to the ability of the wing to bend and its flexibility. In the B787, the wings can go up to 8 meters in order to compensate for the wind and turbulence. This characteristic of the Dreamliner increases fuel efficiency, which is directly related to a reduction in carbon emissions, contributing to the effort to slow global pollution, as well as giving better performance in terms of aerodynamics. The flex reduces drag force and redistributes the stress the aircraft takes, which makes the flight much more stable.
This is possible because plane wings are constantly being designed so that they have lighter weight and are made up of lightweight materials such as carbon fiber-reinforced plastic. Carbon fiber provides efficiency by its characteristic of being light but also being strong simultaneously. The wings for the B787 have also undergone rigorous testing, such as being bent far more than its designed height to ensure its safety. Its lightness also provides for easier bending during flight. In previous models like the B737s and the A320s, even though their wing flex is existent, they are not as efficient as the ones being produced nowadays. This is the reason why flights might feel more rowdy on domestic journeys, where those previous models are used frequently, than on international journeys, where recent models like the B787 are used. The curved wings of the B787 are also visually striking and are a favorite among aviation enthusiasts.
Lift Force
As such, the reason why swinging wings are better than solid wings has been proven, and how they are safer than most people think. The fundamental question is: “Well, okay, the wing flex helps flexibility and fuel efficiency, but how does a plane wing actually work in the first place?” To start explaining lift, an examination of the two common simplified explanations is essential: the “Bernoulli” camp, and the “Newton” camp.
The “Bernoulli” Camp of LiftÂ
One common way people try to explain lift is through Bernoulli’s principles. This theory is also known as the “equal transit time” or “longer path” theory. This states that since airplane wings are designed to have a longer path on the top than the bottom, the air traveling on the top must travel faster because the top and bottom air molecules should simultaneously reach the edge of the wing. However, the fact that the air molecules have to meet the edge of the plane is not supported by any physics principles. This is a misapplication of the conservation principles that are commonly found in physics.
The “Newton” Camp of Lift
Another common way of explaining lift is derived from a misapplication of Newton’s Third Law, which states that for every action, there is an equal and opposite reaction. This theory is also known as the “skipping stone” theory because it alludes to the way how stones skip on a surface of water. The “Newton” camp advocates for how the “inner flow” of air hits the bottom of the wing, and how that flow is deflected, which causes a reaction force upon the bottom of the wing, and that creates the lift force. However, this is a serious misconception that lift force only involves the bottom side of the wing.
The Correct Explanation of Lift Requires Both Newton and Bernoulli and Takes Paragraphs to Discover the “How”
A better explanation involves both the “Newton” side and “Bernoulli” side explanations. As air molecules come into contact with the airplane wing, the air that splits to the bottom side of the wing is deflected, which the airplane wing exerts a force upon. This creates a reaction force that contributes to the lift. The net force that directs upward is also attributed to the airflow around the wings. The curvature of the wing causes the wing to change the airflow at the upper side of the wing, which leads to an increase in velocity. This velocity increase causes the pressure to decrease according to Bernoulli’s principles, and this causes a pressure difference between the top and bottom, thus a net force of upward lift.
To gain a deeper understanding of how the curvature causes the airflow to increase velocity, and how the action-reaction relationship and pressure combine together to create lift would take a few courses on physics regarding this matter. There is an explanation for how the curvature of the wing causes the airflow on the top to increase: as the airflow is more “constricted” to a narrower path as it travels up the curvature, according to the conservation of volume flow rate, the airflow must speed up, and the speed increases compared to the constriction happening on the bottom of the airplane wing, and that this creates the difference in pressure. However, this is still not a complete explanation, since it does not explain how the streamline pinching comes about. This does make intuitive sense regarding conventional commercial airplanes where the bottom side of the wing is flat; however, it does not provide an explanation for wings of different shapes, such as symmetrical airfoils, where both the top and bottom are curved in the same shape.
Conclusion
Wing curvings are a totally safe phenomenon, and are one of the greatest achievements in aerodynamics. The underlying principles of lift require a combination of physics principles and a complex understanding of it. Next time when you witness your plane wings curving, admire the advent of science and try to picture the airflow that passes through the wing and the force created due to it.
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