Camber, in
aerospace engineeringAerospace engineering is the branch of engineering behind the design, construction and science of aircraft and spacecraft. It is broken into two major and overlapping branches: aeronautical engineering and astronautical engineering...
, is the asymmetry between the top and the bottom curves of an
airfoilAn airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
in cross-section.
Camber in its relation to planing surfaces was first discovered and utilised by Sir George Cayley in the early 19th century in England.
Camber is often added to an airfoil to increase
liftLift may mean:* Lift , a mechanical force generated by an object moving through a fluid* Lift , rising air used by soaring birds and glider, hang glider and paraglider pilots for soaring flight...
and/or increase the critical
angle of attackAngle of attack is a term used in fluid dynamics to describe the angle between a reference line on a body and the vector representing the relative motion between the body and the fluid through which it is moving. In general, the reference line could be any line on any arbitrarily shaped body in...
(the angle at which the airfoil begins to stall).
Camber, in
aerospace engineeringAerospace engineering is the branch of engineering behind the design, construction and science of aircraft and spacecraft. It is broken into two major and overlapping branches: aeronautical engineering and astronautical engineering...
, is the asymmetry between the top and the bottom curves of an
airfoilAn airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
in cross-section.
Camber in its relation to planing surfaces was first discovered and utilised by Sir George Cayley in the early 19th century in England.
Overview
Camber is often added to an airfoil to increase
liftLift may mean:* Lift , a mechanical force generated by an object moving through a fluid* Lift , rising air used by soaring birds and glider, hang glider and paraglider pilots for soaring flight...
and/or increase the critical
angle of attackAngle of attack is a term used in fluid dynamics to describe the angle between a reference line on a body and the vector representing the relative motion between the body and the fluid through which it is moving. In general, the reference line could be any line on any arbitrarily shaped body in...
(the angle at which the airfoil begins to stall). The camber of a wing may vary from wing root to wing tip. Camber is not necessary for the generation of
liftA fluid flowing past the surface of a body exerts a force on it. Lift is defined to be the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is defined to be the component of the fluid-dynamic force parallel to the flow...
, and some airfoils have no camber. Airfoils with no camber (symmetric airfoils) do not generate lift at 0 angle of attack, however. Traditionally the upper camber of an airfoil has been greater than the lower, but some recent designs use negative camber. One such design is called the
supercritical airfoilA supercritical airfoil is an airfoil designed, primarily, to delay the onset of wave drag in the transonic speed range. Supercritical airfoils are characterized by their flattened upper surface, highly cambered aft section, and greater leading edge radius as compared to traditional airfoil shapes...
. It is used for near supersonic flight, and produces a more efficient lift to drag ratio at near supersonic flight than traditional airfoils. Supercritical airfoils employ a flattened upper surface, highly cambered (curved) aft section, and greater leading edge radius as compared to traditional airfoil shapes. These changes delay the onset of wave drag and move that drag further aft on the airfoil.
Adding camber doesn't necessarily increase
lift; it depends on the airfoil shape. If too much camber is added, the flow over the airfoil may not stay attached to the wing even at an angle of attack of zero. When this occurs, we say the flow has separation over the airfoil, if the entire top of the wing has separation, the wing is stalled. Wings with camber don't as a result have the ability to produce more lift in general. Cambered wings will produce lift at zero angle of attack, but as mentioned, too much camber can also be a bad thing.
An additional note is that a designer may reduce the camber on the outboard section of the wings to increase the critical angle of attack (stall angle) at the wing tips. When the wing approaches the stall angle this will ensure that the wing root stalls before the tip - giving the aircraft resistance to falling into a spin.
Definition
The camber of an airfoil can be defined by a camber line, which is the curve that is halfway between the upper and lower surfaces of the airfoil. Call this function
Z(x). To fully define an airfoil we also need a thickness function
T(x), which describes the thickness of the airfoil 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 aircraftA tailless aircraft traditionally has all its horizontal control surfaces on its main wing surface. It has no horizontal stabilizer - either tailplane or canard foreplane . A 'tailless' type usually still has a vertical stabilising fin and control surface...
, because the
momentIn physics, the term "moment" can refer to many different concepts:*Moment of force is a synonym for torque, an important basic concept in physics, civil engineering, and mechanical engineering. In the context of mechanical engineering, the terms are not necessarily interchangeable, but one or the...
about the
aerodynamic centerThe aerodynamic center of an airfoil moving through a fluid is the point at which the pitching moment coefficient for the airfoil does not vary with lift coefficient i.e. angle of attack, . where is the aircraft lift coefficient....
of the airfoil can be 0. A camber line for such an airfoil can be defined as follows (
note that the lines over the variables indicates that they have been nondimensionalizedNondimensionalization is the partial or full removal of units from an equation involving physical quantities by a suitable substitution of variables. This technique can simplify and parameterize problems where measured units are involved. It is closely related to dimensional analysis...
by dividing through by the chord):
An airfoil with a reflexed camber line is shown at right. The thickness distribution for a
NACA 4-series airfoilThe NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics . The shape of the NACA airfoils is described using a series of digits following the word "NACA." The parameters in the numerical code can be entered into equations to precisely...
was used, with a 12% thickness ratio. The equation for this thickness distribution is:
Where
t is the thickness ratio.