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Wikipedia, The lift coefficient (C_{L} or C_{Z}) is a dimensionless coefficient that relates the lift generated by an airfoil, the dynamic pressure of the fluid flow around the airfoil, and the planform area of the airfoil. It may also be described as the ratio of lift pressure to dynamic pressure. Aircraft lift coefficientLift coefficient may be used to relate the total lift generated by an aircraft to the total area of the wing of the aircraft. In this application it is called the aircraft lift coefficient C_{L}. The lift coefficient C_{L} is equal to:
The aircraft lift coefficient can be approximated using the Liftingline theory. Section lift coefficientLift coefficient may also be used as a characteristic of a particular shape (or crosssection) of an airfoil. In this application it is called the section lift coefficient c_{l}. It is common to show, for a particular airfoil section, the relationship between section lift coefficient and angle of attack. It is also useful to show the relationship between section lift coefficient and drag coefficient. The section lift coefficient is based on the concept of an infinite wing of nonvarying crosssection. It is not practical to define the section lift coefficient in terms of total lift and total area because they are infinitely large. Rather, the lift is defined per unit span of the wing (L'). In such a situation, the above formula becomes: where c is the chord length of the airfoil. The section lift coefficient for a given angle of attack can be approximated using the Thin Airfoil Theory.
The lift coefficient is a dimensionless number. Note that in the graph here, there is still a small but positive lift coefficient with angles of attack less than zero. This is true of any airfoil with camber (asymmetrical airfoils). On a cambered airfoil at zero angle of attack the pressures on the upper surface are lower than on the lower surface. See also
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Published  July 2009
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