Airfoil (English)

An airfoil is the two-dimensional cross-section of objects that move through a fluid, such as wings, propellers, rudders, or sails. These sections are designed to provide the optimal lift-to-drag ratio for vehicles moving through fluids like air or water. Typically curved or flat, and often resembling a teardrop shape, airfoils function by creating a pressure difference on their two opposing surfaces based on Bernoulli’s principle. This pressure difference generates aerodynamic forces, enabling airplanes to stay aloft.

Airplane Wing

The geometry of an airfoil determines how air flows around it, which is one of the most critical factors in enabling flight. An airfoil has two primary surfaces:

• Upper Surface: Usually convex, it allows air to flow faster, creating a low-pressure area and generating lift based on Bernoulli's principle.
• Lower Surface: Often flatter or concave, it causes slower airflow and generally higher pressure.

Key Airfoil Concepts

1. Leading Edge: The front edge where the air first contacts the airfoil.
2. Trailing Edge: The rear edge where the air leaves the airfoil.
3. Chord Line: A straight line connecting the leading and trailing edges.
4. Camber: The curvature of the airfoil, influencing lift generation.
5. Thickness: The measurement of the airfoil’s thickest part, which impacts aerodynamic performance.

Airfoil concepts

Airfoils are optimized based on flight speed, the purpose of the aircraft, and its mission profile. For instance:

• High-speed aircraft use thinner airfoils to minimize drag.
• Aircraft that perform at lower speeds or require greater maneuverability use thicker, more cambered airfoils.

In a typical airfoil, the curved upper surface creates a longer path for airflow than the lower surface. This causes air on the upper surface to move faster, reducing pressure compared to the lower surface. This pressure difference generates aerodynamic lift.

Lift Force Generation

Aerodynamic lift is created as a result of the interaction between the airfoil and the incoming airflow. This force keeps the aircraft airborne and can be explained using two key principles:

Bernoulli’s Principle

The shape of the airfoil causes differences in airflow speed across its surfaces:

• Upper Surface: The convex curvature makes air travel faster, creating a lower-pressure zone.
• Lower Surface: Slower airflow over the flatter surface results in higher pressure.

This pressure differential produces lift, with the higher pressure underneath pushing the airfoil upward.

Newton’s Third Law of Motion

The lower surface of the airfoil deflects airflow downward. According to Newton’s third law, this downward force creates an equal and opposite upward reaction, contributing to lift.

Airfoil Dynamics During Takeoff

Several factors are crucial during an aircraft’s takeoff:

• Angle of Attack (AoA):The angle between the chord line and the incoming airflow. Increasing the AoA enhances lift but can lead to stall if the angle exceeds a critical point.
• Airflow Velocity:As airspeed increases, more air passes over the wing, generating greater lift. This is why aircraft accelerate during takeoff.
• Wing Shape and Profile:The airfoil’s thickness, camber, and surface area directly affect lift generation.

Takeoff Process

1. Engine Thrust: The aircraft’s engines accelerate it forward, increasing airflow over the wings.
2. Angle of Attack Adjustment: The pilot increases the AoA to generate more lift.
3. Lift Generation: The combination of airflow speed and AoA produces sufficient lift to counteract the aircraft’s weight.
4. Takeoff: When lift exceeds gravity, the aircraft leaves the ground.