Question

The infinite downwash at the wing tips for a single horseshoe vortex in Prandtls lifting line theory was a wrong result. Which of the following does not relate to the correction made?

(a) Superimposition of horseshoe vortices

(b) Lifting line along the span

(c) Trailing vortices only at the tip

(d) Different length of bound vortices

The question was posed to me during an online exam.

Query is from Prandtl’s Classical Lifting-Line Theory topic in division Flow over Airfoils over Finite Wing of Aerodynamics

Answer 1

Right choice is (c) Trailing vortices only at the tip

Best explanation: The downwash due to a single horseshoe vortex in Prandtls lifting line theory gave a wrong result as infinite downwash at the wing tips. This was corrected by assuming a superimposition of many horseshoe vortices, each with different length of bound vortices lying along the span on a line, called lifting line. This gave many trailing vortices distributed along the span as well.