ESDU 80006 provides a means of estimating the drag increment due to rear fuselage upsweep. It is based on information derived from several studies of the problem carried out with wind-tunnel models in Canada, Germany, Sweden, UK, and USA, representing a wide range of practical configurations. The recommended method of estimating the difference in drag coefficient between similar fuselages with and without rear upsweep is based on the "cross-flow drag" concept, using empirical corrections to compensate for the limitations of the method. In this way the data presented can be used to predict all available test results on the drag coefficient increment to within 0.01 of the measured values (based on maximum cross-sectional area of the body). This corresponds to an accuracy better than 5 per cent of the zero-lift drag of an aircraft. The data take account of the effects of downwash generated by the aircraft wing and allow for sharp corners, or corners of small radius, on the perimeter of the fuselage section. The method applies for Reynolds numbers (based on maximum fuselage width) up to 4.4x10E6 and for sub-critical Mach numbers.