ESDU 97021:2012

ESDU 97021 provides a graphical semi-empirical method based on a
correlation of calculations made using a trailing horseshoe-vortex
model to represent a straight-tapered wing with plain flaps over a
range of wing sweeps, taper and aspect ratios, flap chords and
spans, tailplane locations and Mach numbers. It was found that the
data could be represented by taking values for a datum geometry and
Mach number and applying correction factors for departures from
that condition. Predictions by the method were then compared with
wind-tunnel data drawn from the literature and a further factor was
found to be required depending on whether the tailplane was mounted
on the body or on the fin. No effects due to flap type were found
and the effect of a central flap cut out is accounted for in the
lift coefficient used in the method which is that due to flap
deployment. For wings that are not straight-tapered the equivalent
wing concept of ESDU 76003 may be used. The method applies to
fully-attached flow with linear aerodynamic characteristics (an
angle of attack range from -3 to 12 degrees is suggested). Overall,
the mean downwash angle is predicted to within 15 per cent as shown
by a sketch comparing predictions with experimental results. A
fully-worked example illustrates the use of the method. A computer
program of the method is provided as ESDUpac A9721. ESDU 80020
provides a prediction method for the case with flaps
undeployed.