Conclusion: the presence of downwash over a finite wing reduces the angle of attack that each section effectively sees, and moreover, it creates a component of drag ----the induced drag D And this drag is not produced by viscous friction Explanation of induced drag in physical sense a wing-tip vortices destroy the net pressure balance b the wing-tip vortices contain large amount of translational and rotational energy, and this energy serves no useful purpose. In effect, the extra power should be provided by the engine to overcome the the induced dragConclusion: the presence of downwash over a finite wing reduces the angle of attack that each section effectively sees, and moreover, it creates a component of drag ---- the induced drag . And this drag is not produced by viscous friction. Di Explanation of induced drag in physical sense a wing-tip vortices destroy the net pressure balance b the wing-tip vortices contain large amount of translational and rotational energy, and this energy serves no useful purpose. In effect, the extra power should be provided by the engine to overcome the the induced drag