Wing

A wing is a specialized structure designed to move through a fluid, such as air or water.

While we often think of airplanes, wings are defined by two specific characteristics: the airfoil section and the planform. The airfoil is the shape of the wing's cross-section. The planform is the shape of the wing when viewed from above. As a wing moves, it produces two primary forces: lift and drag. Lift is the upward force that opposes gravity. Drag is the air resistance that slows the object down. Engineers measure wing efficiency using the lift-to-drag ratio. This ratio compares the benefit of the lift produced to the resistance of the air.

To understand how lift is produced, we must look at the physics of aerodynamics. Aerodynamics is a branch of fluid mechanics that studies how air moves around objects. One way to explain lift is through the angle of attack. This is the angle at which the wing meets the oncoming airflow. When a wing is tilted at a suitable angle, it deflects the air downwards. This action turns the air mass. Because the wing exerts a force to turn the air down, the air exerts an equal and opposite force on the wing. This reaction force provides the upward component we call lift.

Another way to describe this process involves air pressure. As air moves around the wing, different pressures develop on the surfaces. The top surface of the wing typically has lower-than-ambient air pressure. The bottom surface has a higher-than-ambient air pressure. This pressure difference can be calculated using Bernoulli's principle. This principle relates changes in air speed to changes in air pressure. The higher pressure underneath the wing pushes upward more strongly than the lower pressure on top pushes downward. This imbalance results in a net upward force.

Wings come in many different cross-sectional shapes, known as airfoils. Most wings used for subsonic flight, which is slower than the speed of sound, have an asymmetrical cross-section. These are often called cambered airfoils. However, some aircraft use symmetrical airfoils. These have the same shape on the top and bottom. Symmetrical wings are useful for aerobatic aircraft. They provide the same flight characteristics whether the plane is upright or flying inverted. For flight near the speed of sound, known as transonic flight, engineers use supercritical airfoils. These airfoils are flat on top and curved on the bottom. They are designed specifically to minimize the massive increase in drag that occurs near the speed of sound.

Modern aircraft wings are highly complex and include many moving parts. Pilots use these devices to change the wing's shape and surface area during flight. Leading-edge devices, such as slats or slots, are located at the front of the wing. Trailing-edge devices, such as flaps or flaperons, are located at the back.

Extending these parts increases the wing's area and lift. During landing, pilots might use spoilers on the upper surface. Spoilers increase drag and reduce lift to help the plane slow down and stay on the ground. Some advanced jets even use variable-sweep wings. These "swing wings" can move from an outstretched position for low-speed flight to a swept-back position for high-speed, supersonic flight.

The concept of a wing extends far beyond aviation. In nature, wings have evolved multiple times through different biological paths. Birds, bats, and pterosaurs all evolved wings from existing limbs. In contrast, insect wings evolved as a completely separate structure. Even some plants use wings, such as winged seeds that travel through the air. Humans have applied these same aerodynamic principles to many other machines. Sailboats use sails as vertical wings to move across water. Hydrofoils and submarines use similar shapes, called foils, to move through water. This study of water-based wings is known as hydrodynamics.

Even high-speed land vehicles use the science of wings. Some racing cars, like Formula One cars, use upside-down wings. These airfoils provide greater traction by pushing the car toward the track. In the air, wings can take many planform shapes. These include swept wings, delta wings, elliptical wings, and trapezoidal wings. Whether it is a helicopter's rotating wing or a propeller's blade, the goal is the same: to manage the movement of a fluid to create a specific force. This ability to manipulate airflow is what allows us to explore the skies and the seas.