Question

The correct formula for profile drag coefficient over the finite wing is_______

(a) cd=\(\frac {D_f+D_P}{Sq_∞}\)

(b) cd=\(\frac {D_P}{Sq_∞}\)

(c) cd=\(\frac {D_f}{Sq_∞}\)

(d) cd=\(\frac {D_f+D_P+D_i}{Sq_∞}\)

The question was asked in an internship interview.

The origin of the question is Downwash and Induced Drag topic in division Flow over Airfoils over Finite Wing of Aerodynamics

Answer 1

Correct choice is (a) cd=\(\frac {D_f+D_P}{Sq_∞}\)

The explanation: The profile drag for a wing is the drag caused by viscosity. For moderate angles of attacks, it is same as that for airfoils i.e. a combination of skin- friction drag and pressure drag. The correct formula is cd=\(\frac {D_f+D_P}{Sq_∞}\).