Camber is the asymmetry between the upper and lower surfaces of an airfoil, measured as the maximum distance between the mean camber line (the curve equidistant from upper and lower surfaces) and the chord line. It is expressed as a percentage of chord — a “4% camber” airfoil has a mean line that deviates from the chord by 4% of the chord length at its maximum point.
Cambered airfoils produce lift at zero angle of attack. This means a cambered wing can cruise in a level attitude while still generating the lift needed for flight, reducing fuselage drag. The trade-off is a higher pitching moment — cambered airfoils tend to pitch nose-down — which must be trimmed by a tail surface or reflex at the trailing edge.
Symmetric airfoils (zero camber) produce no lift at zero AoA. They are used on acrobatic aircraft that must fly equally well inverted, and on some UAV vertical tails and control surfaces.
Reflex camber — where the trailing edge curves upward — produces a nose-up pitching moment, enabling tailless and flying-wing configurations to trim without a dedicated horizontal stabilizer. This is essential for delta and flying-wing UAV planforms that lack a tail.
At low Reynolds numbers (small UAVs, slow flight), the amount and distribution of camber strongly affects whether the boundary layer transitions smoothly from laminar to turbulent or separates into a drag-inducing bubble. Excessive camber at Re < 100,000 can increase drag rather than reduce it.
Related terms
- Airfoil — the cross-sectional shape that camber describes
- Angle of Attack — the variable that, with camber, determines lift coefficient
- Chord — the reference length against which camber is measured