ESDU 77012 gives a method for estimating the forward shift of aerodynamic centre by treating the nacelle as an annular wing of diameter equal to the nacelle spanwise width. A graph gives the lift-curve slope for an annular wing as a function of its width to length ratio@ the lift is assumed to act at the nacelle lip@ and a correction term for the effect of the wing upwash field is added. The method is validated by comparing predictions with wind-tunnel data taken from the literature for both free-flow nacelles and nacelles with variable mass flow and is found to predict the shift to within 0.02 of aerodynamic mean chord. The wing lift-curve slope@ also required in the method@ is obtained from ESDU 70011 and the aerodynamic centre of the wing-fuselage combination@ to which the forward shift is applied@ is obtained from ESDU 76015. The effect on aerodynamic centre due to rear-fuselage pylon-mounted nacelles is obtained from ESDU 78013. The computer program ESDUpac A1309@ associated with ESDU 13009@ evaluates the chordwise position of the aerodynamic centre of wing-fuselage-nacelle combinations at subsonic speeds.