D p = ∮ p n ⋅ i d S , Y = ∮ p n ⋅ j d S . displaystyle start off aligned D_ p &=oint pmathbf n cdot mathbf i ;mathrm d S,Y&=oint pmathbf n cdot mathbf j ;mathrm d S.finish aligned  Angle of assault of an airfoil The angle of attack could be the angle between the chord line of an airfoil as well as oncoming airflow. A symmetrical airfoi