# What is the true formula for parasite drag?

I found this site with formulas to calculate for the parasite drag. But I wondered if these formulas are to calculate parasite drag or the parasite drag coefficient? So do you have to multiply the calculated value with the square of the velocity, as in the formula for the general drag force?

I also wonder if there is a difference between the wetted area of an airfoil and the normal planform area?

– user2821
Commented Dec 21, 2014 at 9:11
• I mean this formula: f = kc_fS_wet Commented Dec 21, 2014 at 11:03

• @SimonRavelingien: The drag coefficient itself is dimensionless, so it is independent of scale, area or speed. The drag area is no dimensionless coefficient any more, but depends on the size of the corresponding part $S_{object}$. By multiplying it with dynamic pressure, you get the drag force of the part. Add all parts up, and you have the total drag. Only when you want to get one drag coefficient for the whole airplane, you need to scale the contributions of single parts with their relative area $\frac{S_{object}}{S_{total}}$. A factor like $\frac{S^2_{object}}{S_{total}}$ is never needed. Commented Nov 15, 2014 at 16:02