In aeronautics and aeronautical engineering, camber is the asymmetry between the two acting surfaces of an airfoil, with the top surface of a wing commonly being more convex. An airfoil that is not cambered is called a symmetric airfoil. The benefits of cambering were discovered and first utilized by George Cayley in the early 19th century.
Overview
Camber is usually designed into an airfoil to maximize its lift coefficient. This minimizes the stalling speed of aircraft using the airfoil. An aircraft with cambered wings will have a lower stalling speed than an aircraft with a similar wing loading and symmetric airfoil wings. An aircraft designer may also reduce the camber of the outboard section of the wings to increase the critical angle of attack at the wingtips. When the wing approaches the stall this will ensure that the wing root stalls before the tip, giving the aircraft resistance to spinning and maintaining aileron effectiveness close to the stall. Some recent designs use negative camber. One such design is called the supercritical airfoil. It is used for near-supersonic flight and produces a higher lift-to-drag ratio at near supersonic flight than traditional airfoils. Supercritical airfoils employ a flattened upper surface, highly cambered aft section, and greater leading-edge radius as compared to traditional airfoil shapes. These changes delay the onset of wave drag.
Definition
Broadly, an airfoil is said to have a positive camber if, as is commonly the case, its upper surface is the more convex. But camber is a complex property that can be more fully characterized by an airfoil's camber line, the curveZ that is halfway between the upper and lower surfaces, and thickness functionT, which describes the thickness of the airfoils at any given point. Then, the upper and lower surfaces can be defined as follows:
Example – An airfoil with reflexed camber line
An airfoil where the camber line curves back up near the trailing edge is called a reflexed camber airfoil. Such an airfoil is useful in certain situations, such as with tailless aircraft, because the moment about the aerodynamic center of the airfoil can be 0. A camber line for such an airfoil can be defined as follows : An airfoil with a reflexed camber line is shown at right. The thickness distribution for a NACA 4-series airfoil was used, with a 12% thickness ratio. The equation for this thickness distribution is: Where t is the thickness ratio.
