Finite Wings - Performance Loss

The same airfoil (infinite wing) when used as a wing suffers

• a loss of lift - as the slope of the lift curve changes because of the downwash created by the strong tip vortices
• an increase in drag - lift induced drag because of the component of lift in the direction of drag

Increase in Drag - D_i (Induced Drag)

Loss of Lift

In the figure a 3D wing (blue color) and a corresponding 2D wing above (red color) [same airfoil, same chord] are shown. At any section

• the tip vortices introduce a vertical component of velocity which causes an induced angle of attack relative to the infinite wing. This causes an effective angle the attack to be correspondingly lower, therefore generating a lower lift coefficient for the section
• the lift vector by definition is normal to the relative velocity. This causes a component of drag in the direction of the free stream. This is called the lift induced drag - or - induced drag