Related Resources: fluid flow

Aerodynamics Airfoil Theory Equations

Engineering Fluids

Aerodynamics Airfoil Theory Equations

The lift force on an airfoil is given by

lift force

CL = the lift coefficient
V = velocity (m/s) of the undisturbed fluid and
Ap = the projected area of the airfoil as seen from above (plan area). This same area is used in defining the drag coefficient for an airfoil.

The lift coefficient can be approximated by the equation:

CL = 2 π k1 sin ( α + β ) which is valid for small values of α and β

k1 = a constant of proportionality
α = angle of attack (angle between chord of airfoil and direction of flow)
β = negative of angle of attack for zero lift.

The drag coefficient may be approximated by:

The drag coefficient

CD∞ = infinite span drag coefficient

infinite span drag coefficient

The aerodynamic moment is given by:

aerodynamic moment

where the moment is taken about the front quarter point of the airfoil.

MC = moment coefficient
Ap = plan area
c = chord length



Fundamentals of Engineering, seventh Edition National Council of Examiners for Engineering amd Surveying