D p = ∮ p n ⋅ i d S , Y = ∮ p n ⋅ j d S . displaystyle start out aligned D_ p &=oint pmathbf n cdot mathbf i ;mathrm d S,Y&=oint pmathbf n cdot mathbf j ;mathrm d S.stop aligned  Angle of assault of the airfoil The angle of assault may be the angle between the chord line of an airfoil plus the oncoming airflow. A symmetrical airfoil ge