In reality, the air velocity could vary in all three dimensions, and that air could also flow upwards or downwards. However, when it comes to the forces exerted on the airfoil, it’s only the pressure right at the surface of the airfoil that matters. Conversely, for a downward tilted airfoil, the pressure forces push the airfoil down. Airfoil ShapesLet’s go back to the simple symmetric airfoil we’ve been playing with thus far. The velocity of the flow around the airfoil is also a contributing factor to the design of the shape.