Coefficient of lift

The coefficient of lift is a number associated with a particular shape of aerofoil, and is incorporated in the lift equation to predict the lift force generated by a wing using this particular cross section.

Note that the lift equation does not include terms for angle of attack - that is all wrapped up within the coefficient of lift term. The graph for lift coefficient vs. angle of attack follows the same general shape for all aerofoils, but the particular numbers will vary. The graph shows a linear increase in lift coefficient with increasing angle of attack, up to a maximum point, after which the lift coefficient falls away rapidly. This is known as the stall angle of the aerofoil.

The coefficient of lift is a dimensionless number.

Note that in the graph here (which is generic, not representing any particular aerofoil), there is still a small but positive lift coefficient with angles of attack less than zero. This is true of many actual designs - the curvature of the aerofoil will still create a small amount of lift at small negative angles.