ESDU Aero C.01.01.01 gives graphs for the lift-curve slope derived by correlating results of wind-tunnel tests on models without simulated propeller slipstream. The lift-curve slope is based on an effective area for the fin and rudder that includes the fuselage area directly below the fin root chord (where there is a small fillet the root chord is defined by extending the fuselage top line and fin leading edge to intersect; the effect of large fillets is not covered). The method involves obtaining the lift-curve slope of a rectangular wing of equivalent aspect ratio that allows for the end plate effect of the tailplane. Graphs plot: (i) the ratio of the fin and rudder lift-curve slope to that of the rectangular wing, (ii) the lift-curve slope of the rectangular wing as a function of the equivalent aspect ratio and the trailing-edge angle of the rudder, and (iii) the equivalent aspect ratio as a function of the tailplane position on the fin. It is noted that there is also an effect of wing position on the fin and rudder lift-curve slope but it is believed that effect is covered by a scatter band shown on the graph plotting the lift-curve slope ratio. The effect of a gap between the fin and rudder may be treated by the method of ESDU Aero C.01.01.04. A method for estimating the centre of pressure for the sideforce is suggested. The lift-curve slope is predicted to within 10 per cent. For fins mounted on a circular fuselage ESDU 82010 should be consulted while for twin fins and rudders ESDU 92007 may be used.