# How do viscous drag and form drag individually change as a function of angle of attack?

Typically, when dealing with airfoils, the drag coefficient $$C_d$$ is given as a function of angle of attack. If we limit the discussion to 2D subsonic incompressible flows, then the drag is the sum of the viscous drag and the form drag (pressure drag), equivalently:

$$C_d = C_{d,\text{visc}} + C_{d_,\text{form}}$$

Where: $$C_{d,\text{visc}}$$ is the viscous drag coefficient, and $$C_{d_,\text{form}}$$ is the form drag coefficient.

I've never seen, these coefficient plotted as function of angle of attack individually. That is, $$C_{d,\text{visc}}=f(\alpha)$$, or $$C_{d_,\text{form}} = f(\alpha)$$.

The reason I want to see them plotted individually, is to emphasize the contribution of each type of drag (qualitatively, I know that for angles of attack below stall, the viscous drag is higher than form drag, but for angles beyond the stall, (boundary layer separation), the form drag dominates).

Are there any graphs showing these coefficients individually, say for NACA airfoils?

• do u want a graph all the way up to 90 degrees or just stall? – Abdullah Jun 19 '20 at 10:12
• Viscous drag probably won't change much if you don't change configuration, but considering form drag is very good. This would be part of induced drag (making lift). Interestingly, form drag also comes into play when one uses excess lift as a propeller. – Robert DiGiovanni Jun 19 '20 at 11:05
• @Abdullah: I think up to 30 degrees will be sufficient. – IamNotaMathematician Jun 19 '20 at 13:19