Camber

Camber is the maximum deviation of the camber line (which is the bisector of the profile thickness) from the chord of the profile, as illustrated in Figure 1.11.

Let zu and zi be the ordinates on the upper and lower parts of the profile, respectively, for the same value of x. Let c be the chord, and the x-axis coincide with the chord. Now, the upper and lower camber are defined as:

Upper camber = Lower camber

where the subscript “max” refers to that ordinate which is numerically the greatest. Camber is taken as positive or negative according to the sign of (zM)max and (z;)max. Also, at a given x, the magnitudes of (zu)max and (zl)max may be different for unsymmetrical profiles.

The camber line is defined as the locus of the point (x, 2 (zu + zi)). In the case of symmetrical profile zu + zl — 0, and the camber line is straight and coincides with the chord. Denoting the numerically greatest ordinate of the camber line by zmax, we define:

Mean camber = ^max.

c

Note that the mean camber, in general, is not the same as the mean of upper and lower camber, and the mean camber of a symmetrical profile is zero. Usually the word camber refers to the mean camber.

The thickness ratio of an aerofoil is the ratio of the maximum thickness (measured perpendicular to the chord) to the chord. The thickness ratio is essentially tmax/c.

From the above discussions, it is evident that:

• Camberline of an aerofoil is essentially the bisector of its thickness.

• Camber is the deviation of the camberline from the chord, namely the shortest line joining the leading and trailing edges of the aerofoil profile.

• The local camber can vary continuously from the leading edge to the trailing edge. Therefore, the max­imum camber is taken as the representative camber. That is, the maximum ordinate of the camberline from the chord is taken as the camber of an aerofoil.

• The thickness of an aerofoil profile also varies continuously from the leading edge to the trailing edge. Therefore, the ratio of the maximum thickness:

tmax — i^Zu, max + Zl, max )/2

to chord c is used to represent the thickness-to-chord ratio of an aerofoil.