Lift is calculated by plotting the non-dimensional static pressure (Cp) vs. the non-dimensional chordwise location (x/c) of the pressure tapping as below. This distance is non-dimensionalised by the chord length, so it varies from 0 to 1

The area inside the curve, which is found by integration, is the normal force coefficient (Cn), the normal force being that perpendicular to the chord line regardless of angle of attack. Pressure drag is calculated by plotting the non-dimensional static pressure (Cp) vs. the non-dimensional location above or below the chord line (y/c) of the pressure tapping as below. This distance is non-dimensionalised by the chord length, so it varies from 0 to some positive and negative non zero number depending on the section thickness

The area inside the curve, which is found by integration, is the tangential force coefficient (Ct), the tangential force being that parallel to the chord line regardless of angle of attack. My integration gives Cn as 0.4006 and Ct as -0.02732.

Once you have Cn and Ct, you resolve trigonometrically using the angle of attack (a) to get the lift (Cl) and pressure drag (Cdp) coefficients as below.

Cl = Cn cos(a) - Ct sin(a)

Cdp = Cn sin(a) + Ct cos(a)

The pressure distributions shown were taken at an angle of attack of 4 degrees, thus using the above; I get Cl as 0.402 and Cdp as 0.001.

Anytime the pressure coefficient curve crosses over itself, such as the Cp vs. y/c example above, the alternate closed areas will make positive and negative contributions to either the normal or tangential force coefficient. Such crossing over occurs much more frequently for the Cp vs. y/c curve.

Regards, JetMech