Formation Flight :

                
             Tip vortices, as already discussed as originating from the tips of the wings, are generally not very desirable, as they enhance induced drag.


        However, some flyers utilize this very drawback, to fly at a lesser cost of energy!

        Birds flying in a V formation - a common sight in the sky - do just that.

        The vortex system generated by each bird has a downwash within the system, but has an upwash just outside it. So, if a bird positions itself in the upwash created by the bird ahead of it, it experiences an upward lift!

        Hence, except for the bird at the tip of the V, all the others utilize the upwash generated by the member ahead of them. Therefore, the position at the tip is switched more often, than any other position, as it requires the most amount of work.