ESDU 80020:2012

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 acceptable in the method. The method applies only to
wing-body-tail combinations although some assessment of the effect
of rear-fuselage mounted nacelles is given. A computer program of
the method is provided as ESDUpac A8020. ESDU 97021 provides a
method for estimating the effect of flap deployment on the average
downwash angle at the tailplane low speeds.