For the case of infinite horseshoe vortices along the lifting line, a vortex sheet exists which_________
(a) Is formed by continuous trailing vortices
(b) Is perpendicular to free-stream velocity
(c) Total strength is zero
(d) Equal and opposite trailing vortices
I had been asked this question during an interview.
This key question is from Prandtl’s Classical Lifting-Line Theory topic in section Flow over Airfoils over Finite Wing of Aerodynamics