Ground effect is the floating of an aircraft when it is near the ground on landing. “Ground effect” generally comes into “effect” when the aircraft’s height from the ground is nearly half-the length of the aircraft’s wingspan.

When an aircraft flies it creates wing tip vortices. On approaching to the ground during landing, the strength of wing tip vortices get diminished, because of interaction with the ground. Wing tip vortices creates downwash which results in induced drag. Since, strength of the wing tip vortices is reduced, therefore, the downwash and strength of the induced drag is reduced. This is called the ground effect which results in airplane’s tendency to “flare” and float above ground when the aircraft is at the moment of landing.

The reduced drag can be accounted by an expression, given by McCormick as \[\alpha = \frac{{{{\left( {16a/b} \right)}^2}}}{{1 + {{\left( {16a/b} \right)}^2}}}\]

Here,  ‘a‘ is the height of the airplane’s wing above the ground and ‘b‘ is the span of the wing. Here, Induced drag will be reduced by a factor ‘\(\alpha \)’ which is less than or equal to one.

Induced drag is \[{C_{D,i}} = \alpha \frac{{C_L^2}}{{\pi eAR}}\]

Application of ground effect