ESDU 13009 describes the construction of input files for the program ESDUpac A1309@ which combines the prediction methods of three individual ESDU Data Items (ESDU 76015@ 77012 and 78013) to evaluate the chordwise position of the aerodynamic centre of wing-fuselage-nacelle combinations at subsonic speeds. The nacelles can be mounted either on pylons below the wings of wing-fuselage combinations of medium-to-high aspect ratio@ or on short pylons on the rear fuselage of wing-fuselage combinations.