Abstract:

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.