ESDU 79015 gives two methods for estimating the drag; one is an approximate method for use at the project stage when the geometry is not fully defined and gives the overall drag@ and the second is for use when the geometry is known and sums the individual contributions of each component with allowance for interference. For the first method a correlation of flight measured drags on civil transports led to a simple equation with an empirical constant whose value depends on whether flaps are deflected or not. For the second method graphs are provided by which the drags of wheels@ struts@ undercarriage bay and undercarriage doors can be predicted and the interference effects of multiple wheels and struts@ and of flaps and wing with the installation@ can be estimated. The data can be used with retractable or fixed undercarriages for which data deal with the drag of streamlined struts and spats. Comprehensive worked examples illustrate their use.