ESDU 76026 gives a method, based on an analysis of a limited number of experimental data taken from the literature, for predicting the effect of spoiler deflection. The method predicts the download due to the spoiler by treating it as a split flap and applying ESDU 74009 and 74012, and also predicts the reduction in lift due to the flaps covered by the spoiler whether of the deflecting-shroud or fixed-shroud type. The change in lift is used to predict the contribution to the change in lift dependent drag, while the drag due to the spoiler itself is evaluated by an empirically based formula. The method predicts the change in lift coefficient to within 0.1 and the change in drag coefficient to within 0.03.