Camber refers to the asymmetry between the upper and lower surfaces of an airfoil, a geometric property expressed as the curvature of those surfaces. An airfoil, defined as the cross-sectional shape of a lifting surface, has a mean camber line drawn halfway between its upper and lower surfaces; this line passes through every midpoint of the profiles. When the mean camber line lies above the chord line, the airfoil possesses positive camber, while a reflex-camber surface positions the line below the chord. The maximum distance between chord and mean camber line is termed maximum camber, and this maximum is typically situated ahead of the point of maximum thickness. Such cambered geometry allows an airfoil to generate positive lift even at zero angle of attack, and its extent and distribution strongly influence stall behavior. Airfoil design balances camber with thickness to achieve desired aerodynamic performance.
What is camber in airfoil?
Camber is the curvature of an airfoil. The mean camber line is an imaginary line that lies halfway between the upper surface and lower surface. This line intersects the chord line at the leading and trailing edges, and it can curve above or below the chord line. The camber value gives the highest value above or below the chord line divided by the chord length.
Camber is the curvature of the mean line, the line equidistant from the top and bottom of the wing, measured perpendicular to the chord. In a cambered airfoil, the upper surface is markedly curved while the bottom surface has no or only minimum curve. At some point the bottom face becomes concave. This asymmetry makes camber a vital feature of an airplane wing because it helps the wing generate lift at lower angles of attack. An example is the Clark Y airfoil, whose curved upper surface and nearly flat lower surface illustrate how camber increases the pressure difference between the two sides, letting the aircraft fly efficiently without relying solely on angle of attack.
What is the difference between cambered and symmetric airfoil?
The difference between a cambered airfoil and a symmetric airfoil is that in a cambered airfoil, the upper and lower surfaces are not symmetric. A cambered airfoil has asymmetry between the two acting surfaces: the top surface is more convex, while the bottom is flatter. This built-in curvature produces lift even at zero angle of attack. A symmetric airfoil has no camber; its upper and lower surfaces are mirror images, so camber is zero. Because the distance for air to travel is equal on both sides, pressure distribution is identical at zero angle of attack, giving zero lift there.
High-camber wings carry more curvature, generating greater lift at low speed, whereas low-camber wings trade some lift for lower drag. Cambered wings generally have higher drag than symmetric wings, yet they reach higher maximum lift coefficients. Symmetric wings, lacking curvature in shape, are well suited for inverted flying and are used extensively in rotor-wing applications where equal upside-down performance is required.
What does camber do to an airfoil?
Camber is designed to minimize the drag coefficient, postpone stall, and maximize lift, all of which permit lighter, slower, and more efficient flight. The purpose of a cambered airfoil is to create lift by establishing a favorable pressure difference above and below the surface. High-lifting airfoil surfaces minimise adverse pressure gradients on the upper side, and adding camber delays flow separation, lowering drag and reducing the stalling speed. Maximum lift coefficient is thus raised, so the aircraft can stay aloft at lower speed.
Camber is vital for flight because it provides aerodynamic advantages across the speed range: it helps subsonic flight for supersonic aircraft, and when maximum camber is placed within the front of the wing it gives an ideal pressure distribution. Camber near the rear end increases the pitch moment coefficient. Increasing camber therefore raises pitching moments while leaving the aerodynamic center unchanged. Designers exploit this by designing camber so that the tip stalls slower than the root, preserving aileron control.
How does the camber of an airfoil affect lift?
The camber of an airfoil affects lift by increasing or decreasing the lift coefficient. A higher camber generates more lift at lower angles of attack because the pronounced curvature of the upper surface accelerates the flow, creating a favorable pressure difference that results in greater lift. The location of maximum camber matters: moving maximum camber forward, especially toward the leading edge, increases maximum lift coefficient and delays stall, whereas aft camber shifts trade maximum lift for lower pitching moments. Mean camber therefore acts as a very strong function of airfoil performance. Cambering, first discovered and utilized by George Cayley, allows lift to be obtained at smaller angles and with lower drag.
What is the zero lift line of an airfoil?
The zero lift line of an airfoil is a line representing the angle of attack where the aerofoil produces no lift. Cambered aerofoils generate no lift when moving parallel to an axis called the zero-lift line. The angle of attack on an aerofoil is measured relative to the zero-lift axis, which is better than the chord line for describing the angle of attack.
The zero-lift line is the angle-of-attack reference along which the section produces no lift. For symmetrical aerofoils this line coincides with the chord line, so the zero-lift angle is zero degrees. For cambered sections the zero-lift line is rotated relative to the chord. The thin-aerofoil theory places it between -3 and -1.5 for most practical shapes. Camber therefore shifts the whole lift curve: the same physical shape that raises lift at moderate angles also moves downward, so the wing must be set at a higher incidence to make the aircraft fly at the same lift coefficient.
What is the difference between positive and negative camber airfoils?
Positive camber is when the upper surface is more convex, while negative camber is when the lower surface is more convex. This single geometric distinction produces opposite aerodynamic moments: the moment is normally negative for positive camber and positive for negative camber. Positive camber airfoils have negative pitching moment, and negative camber airfoils have positive pitching moment. The zero-lift pitching moment is usually negative for positive camber and positive for negative camber.
The sign of the pitching moment governs stability. A negative moment from a positively cambered section tends to nose the aircraft down, a feature that conventional tailplanes exploit. A positive moment from a negatively cambered section noses the aircraft up, an effect that, in principle, aids straight-wing tailless aircraft because the wing itself supplies the required download at the trailing edge. Negative camber airfoils are not generally used: the same curvature that creates the positive moment leads to higher drag, and the structural and control penalties outweigh the theoretical gain.
What is reflexed camber airfoil?
A reflexed camber airfoil is an airfoil where the camber line curves back up near the trailing edge and this upward curvature produces an S-shaped camber line.
Why is a reflexed camber used on an airfoil? Reflexed camber is used on an airfoil to obtain zero pitching-moment with lift, to obtain zero change in trim with angle of attack, and to make the moment about the aerodynamic center of the airfoil equal to 0. On tailless aircraft, flying wings, helicopters, and autogiros, it provides longitudinal stability without the need for a separate tailplane because the reflexed camber line reduces the pitching moment and makes the moment coefficient at c/4 positive. Modifications to certain NACA series include the addition of reflex camber to produce zero pitching moment, helping to stabilize these configurations without separate tailplane surfaces.
What is conical camber in an airfoil?
A conical camber in an airfoil is a camber for which the surface slope is constant along rays through the wing apex. Load and upwash are therefore uniform along the same rays. Conical camber is an important class of camber distributions associated with the planform and uses more camber toward the wingtips and changes opposite to those produced by Dunne's wing. NACA defined a specific version under the name NACA conical camber, later exemplified on the F-15 wing. Wind-tunnel results show that such a design reduces drag due to lift at high subsonic and transonic speeds for lift coefficients above 0.15, yet offers diminishing returns at supersonic speeds.
What is a variable camber airfoil?
A variable camber varies the camber of the airfoil surface during flight. It acts by altering the shape of flexible upper and/or lower skins, driven by a front spar assembly that extends spanwise through the airfoil and a rotary actuator that actuates the camber altering linkage. This mechanism allows seamless re-contour of the airfoil leading and trailing edges, eliminating gaps and surface discontinuities.
Morphing capability is embodied in the Variable Camber Compliant Wing (VCCW), an adaptive structure that behaves much like a bird's wing. Continuous wing reconfiguration optimizes wing geometry for current altitude, airspeed, and lift-to-drag ratio requirements. Wind-tunnel and flight tests show greatest improvement in the transonic region, while profile drag is reduced after release of armament load and noise is lowered through smooth, seamless geometry changes.
How is airfoil camber measured?
All airfoil camber measurements are taken perpendicular to the chord which is deemed to have a length of 1 or 100%. The total camber of an airfoil is the greatest such distance found anywhere between the leading edge and the trailing edge. By convention it is expressed as a percentage of the chord, so a camber of 2% means the maximum camber distance equals 2% of the chord length. The camber ratio is simply this same value written in ratio form; for example the ratio is 0.02 when camber is 2%.
How to calculate camber line of airfoil?
To calculate the camber line of an airfoil follow the steps explained below.
- Calculate camber line for 5-digit airfoil using yc = k1/6 (x3 - 3rx2 + r2 (3-r)x)
- Calculate camber line for 4-digit airfoil using yc = M/p2 (2Px - x2)
- Calculate upper surface coordinate using xU = x - yt sin θ and yU = yc + yt cos θ
- Calculate lower surface coordinate using xL = x + yt sin θ and yL = yc - yt cos θ
These camber line equations describe the curved line representing the average contour of both upper and lower surfaces.
What is the center of pressure on an airfoil?
The center of pressure of an aircraft is the point where all of the aerodynamic pressure field may be represented by a single force vector with no moment, and the center of pressure on a symmetric airfoil lies close to 25% of the chord length behind the leading edge of the airfoil. The center of pressure is the focal point of lift force on the airfoil, the single point where the total sum of pressure forces acts. It is the average location of the pressure variation, a well-defined reference point used to do calculations. Lift and drag forces can be applied at this single point with no extra moment.
The center of pressure is not fixed. Its location is given by cp = ∫ x ✕ p(x) ✕ dx / ∫ p(x) ✕ dx , an area-weighted average obtained by integrating the measured pressure distribution over the chord. For a conventionally cambered airfoil at maximum lift coefficient, the center of pressure lies a little behind the quarter-chord point. When the lift coefficient is zero, the same airfoil's center of pressure is an infinite distance behind the chord, so the point is located outside the physical airfoil. As angle of attack changes the center of pressure moves: it shifts forward at high angles-of-attack and aft toward the trailing edge as angle of attack is reduced. Because this movement complicates stability analysis, engineers prefer the aerodynamic center, a fixed point at quarter-chord for low-speed airfoils, where the pitching moment remains constant with angle of attack.
The airfoil center of pressure calculation starts with pressure taps on the surface: the measured p(x) curve is numerically integrated to find the chord-wise centroid of force. Center of gravity, the average location of the weight of the aircraft, is a separate quantity, yet the two must be compared. If center of pressure and center of gravity coincide the aircraft continues in level flight with no extra trimming force. If the center of pressure moves ahead of the center of gravity the airplane pitches up, and if it moves behind, the airplane pitches down. Thus the shifting center of pressure is key to determining stability and control, while the fixed aerodynamic center eliminates the problem of movement and is used to compute the trim of the vehicle.
What is the equation for the pitching moment of an airfoil?
The pitching moment M of an airfoil is the torque produced by the aerodynamic force with respect to a chosen reference point on the chord. For a two-dimensional segment, the moment per unit length is written m, and its sign convention is nose-up positive. The dimensionless pitching-moment coefficient is defined as Cm = M/qSc̄ . The quarter-chord point is the customary reference for low-speed airfoils because, for incompressible flow, the aerodynamic center lies very close to it and the moment about this point is almost independent of angle of attack.
What is the relationship between airfoil camber and chord?
The chord line is the straight datum that joins the leading edge to the trailing edge, and the chord length is simply the distance between these two points. Because this line is fixed, every measure of camber is expressed relative to it. Thus, all cambered airfoils have a camber ratio expressed as a percent of chord, and this camber ratio is the ratio of the maximum camber to the chord length. Maximum camber point is where the mean camber line and chord line have the greatest distance, so the larger the chord, the farther this peak lies from the reference line in absolute terms, but the ratio stays unchanged.
The quarter-chord point, located 25% of the chord length aft of the leading edge, is the aerodynamic center for all cambered airfoils. At this station the moment coefficient about quarter-chord is nearly independent of angle of attack, and the aerodynamic moment about the quarter chord point is roughly twice as large for the airfoil having the larger camber.
What is the relationship between airfoil camber and thickness?
Thickness is added to the camber line, which is curved, and is measured perpendicular to that line, so the maximum distance between upper and lower surfaces is called thickness. The thickness distribution equation supplies the local thickness, while the thickness ratio, together with camber ratio, affects aerodynamic coefficients. Within practical thickness-to-chord ratios, influences on lift and moment are small, yet increasing thickness increases drag mainly because the larger surface enlarges pressure recovery on the rear part. In thin-wing theory, thickness and camber become infinitesimally small and within that limit camber and thickness are coupled to the thickness problem. On thick wing sections the relative influence of thickness ratio is overshadowed by angle of attack and geometric camber, making such sections relatively insensitive to camber. The Clark Y airfoil illustrates these relations: here the maximum thickness is 11.7% at 28% chord, demonstrating the independent specification of camber line and thickness function.
Thicker airfoil offers larger functional completeness and handles airflow at higher angles giving gentler stall features and tolerant air travel operating capability. Slender cambered airfoils could not handle airflow. Narrow flaps did poorly during speed-ups and were prone to resonance. Thus, raising camber without adding thickness drags the suction peak up.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
