ESDU 88029 predicts the adverse yawing moment accompanying aileron deflection as two components@ an induced drag contribution due to the differential setting and a profile drag component. For the first component a semi-empirical correlation procedure is developed while for the second the method of ESDU 87024@ which deals with the profile drag due to deflection of plain flaps@ is used. The method applies to sealed controls (or controls with small gaps) and allows for differential operation and flap deployment. The experimental data drawn from the literature (with some unpublished wind-tunnel measurements) covered a wide range of wing and aileron geometry which is specified. The method predicted the change of yawing moment coefficient per unit control deflection to within 0.003 ad at zero lift and without deployed flaps. A program of the method is provided with ESDU 88040 as ESDUpac A8840.