Question

The incorrect statement for a finite wing with elliptical lift distribution out of the following is_____

(a) Induced drag coefficient ∝ coefficient of lift

(b) Induced drag coefficient increases rapidly with lift

(c) Induced drag coefficient is around 25%

(d) To reduce induced drag, we want wing with the lowest aspect ratio

I had been asked this question during a job interview.

Question is taken from Prandtl’s Classical Lifting-Line Theory in section Flow over Airfoils over Finite Wing of Aerodynamics

Answer 1

Right answer is (d) To reduce induced drag, we want wing with the lowest aspect ratio

The explanation is: The induced drag coefficient varies directly with the square of lift coefficient. Thus, it increases rapidly with the lift. At high speeds, it is around 52% of total drag. For least induced drag, we want high aspect ratio for the wing.