A rapid method for estimating the downwash behind swept-wing airplanes is presented. The basic assumption is that of a flat horizontal sheet of vortices trailing behind the wing. The integrations for the downwash are handled in a manner similar to both Multhopp's and Weissinger's approximate integrations in their span-loading calculations. The principal effects of rolling-up of the wake are treated as corrections to the flat-sheet wake. A simple approximate correction for the effect of the fuselage is applied. The agreement with available experimental data taken behind airplane models is good. Computing forms are included together with charts of pertinent functions, so as to enable simple direct application.