nacelle assembly 26 achieves this etops requirement and maintains an external airflow f 2 which is separation free from the fan cowl 46 current industry standards typically use a diameter ratio of at least approximately 0 80 to achieve a separation free airflow but other diameter ratios may be feasible the nacelle assembly 26 also defines a contraction ratio the contraction ratio represents a relative thickness of the inlet lip section 38 of the nacelle assembly 26 and is represented by the ratio of a highlight area h a ring shaped area defined by highlight diameter d h and a throat area t a ring shaped area defined by throat diameter d t of the nacelle assembly 26 current industry standards typically use a contraction ratio of approximately 1 300 to prevent the separation of the fan discharge airflow f 1 from an interior wall 59 of the fan cowl 46 but other contraction ratios may be feasible u201c thick u201d inlet lip section designs which are associated with large contraction ratios increase the maximum diameter and increase the weight and the drag penalties associated with the nacelle assembly 26 the nacelle assembly 26 further defines an inlet lip length.