ESDU AERO W.02.04.03 gives curves of form factor as a function of thickness/chord ratio and transition position on three types of aerofoils (representative of low-drag aerofoils such as the NACA 6A and RAE 100 to 104 series) defined as having maximum thickness at 0.36@ 0.38 and 0.41 of chord and maximum suction at respectively 0.3@ 0.4 and 0.5 of chord. To obtain the drag of the aerofoils the data for the drag of a flat plate given in ESDU AERO W.02.04.01 is factored by the corresponding value of the form factor obtained from the curves; where transition occurs on the upper and lower surfaces at different positions an average position is assumed.