An airfoil is the specific shape of a wing or blade designed to generate lift when moving through air, enabling aircraft to fly. This article will delve into a key characteristic of airfoils called “camber.”
Defining Camber
Camber refers to the curvature or asymmetry of an airfoil’s shape, describing how its upper and lower surfaces deviate from a straight line. To define camber, a reference known as the chord line is used. This imaginary straight line connects the leading edge (front) and trailing edge (back) of the airfoil.
The mean camber line is drawn equidistant from the upper and lower surfaces, extending from the leading to the trailing edge. Camber is distinct from an airfoil’s thickness, which measures the overall depth of the wing section. The amount of camber is measured as the maximum distance between the mean camber line and the chord line.
Types of Camber
Airfoils can exhibit different types of camber, each suited for specific aerodynamic purposes. Positive camber is the most common type, where the upper surface of the airfoil is more convex or curved than the lower surface. This design is prevalent in most aircraft wings, promoting significant lift generation.
Negative camber occurs when the lower surface of the airfoil is more curved than the upper surface, or when the mean camber line curves below the chord line. While less common for main wings, negative camber can be found in certain high-speed aircraft designs or in specific aircraft components like horizontal stabilizers. Symmetric camber describes an airfoil where the upper and lower surfaces are mirror images of each other, meaning the mean camber line is a straight line coinciding with the chord line. This type of airfoil generates no lift at a zero angle to the oncoming airflow and is often used in aerobatic aircraft or helicopter rotor blades, allowing for efficient inverted flight.
Camber’s Role in Lift Generation
Camber plays a role in how an airfoil generates lift, the upward force counteracting gravity. The curved shape of a cambered airfoil influences airflow over and under its surfaces. Air traveling over the more curved upper surface must cover a greater distance in the same amount of time as air moving along the flatter lower surface.
This difference in travel distance causes air flowing over the top surface to accelerate, reducing air pressure above the wing. Conversely, air beneath the wing moves slower, leading to higher pressure. This pressure differential, with lower pressure above and higher pressure below the wing, creates an upward force, generating lift. A higher degree of positive camber allows for greater lift at lower speeds.
Camber in Aircraft Design
Aircraft designers select the amount and type of camber for different flight conditions. Aircraft designed for high lift at low speeds, such as cargo planes or small propeller aircraft, feature wings with more pronounced positive camber. This enhanced curvature helps generate sufficient lift for takeoff and landing on shorter runways.
High-speed aircraft like fighter jets or airliners utilize wings with less camber, sometimes even minimal or reflexed camber. This design choice reduces drag at high speeds, aiding efficient cruise performance. Aircraft also employ high-lift devices such as flaps and slats to temporarily modify the wing’s camber during specific flight phases. Extending these devices increases the wing’s effective camber, providing additional lift for takeoff and allowing slower, safer landing speeds.