Putting it All Together Remember, as the air turns corners into the flow, the velocity increases hence the pressure decreases. When the air turns corners away from the flow, the velocity decreases and pressure increases. The pressure near a surface causes a force to act on the surface. Pressure is a distributed force. When we add up the distributed force around a lifting airfoil, the resulting force is lift.
Profile drag is due to a thin layer of viscous flow near the airfoil.
If the flow is laminar then that layer is thinner than if the flow is turbulent. The thicker the layer of viscous flow, the greater the profile drag. Induced drag is due to 3-dimensional effects and lift. The graphs and airfoil analysis in this article were done using VisualFoil. Click here for more information.