ESDU 80020 contains a simple method for estimating the average downwash angle at the tailplane for subsonic speeds and low angles of attack where the lift@ pitching moment and downwash characteristics are linear@ i.e. where the flow is wholly attached. The method@ which is semi-empirical@ is a first order one allowing for the major effects of wing planform@ body@ wing-body interference and tailplane height. Moderate amounts of wing twist are also catered for. The method applies only to wing-body-tail combinations although some assessment of the effect of rear-fuselage mounted nacelles is given.