ESDU 06014 provides the increment in the zero-lift drag coefficient of a wing due to the deployment of plain trailing-edge flaps. The increment is to be used within the prediction method for the wing total drag coefficient over the range of total lift coefficient where there is a parabolic variation. The anticipated form of the parabolic variation is implicit in the empirical correlation. The modelling and analysis of the drag polar are discussed in detail. The accuracy of the method is assessed as within 0.015 on the drag coefficient increment. The traditional allowance for the effect of wing sweep is followed after review. The use of the method is illustrated by a worked example.