Drag Coefficient

Janna¹ states that drag coefficient represents the ratio of drag to inertia forces and is written as:

C_d = D_f / 0.5p V² A_p²

Where:

D_f = Drag force (lb_f)
p= Air density (slug/ft³)
V = air velocity (ft/s)
A_p = Projected area (ft²)

¹Janna, William, S., Introduction to Fluid Mechanics, PWS Publishing Company, Boston, 1993.