Abstract:

ESDU 95021 presents an empirical method that depends on determining the increment for an aerofoil representative of the wing and applying factors to allow for three-dimensional and part-span effects. ESDU 94031 is used to predict the increment for the aerofoil, depending on the extended deployed chord. That increment is factored by the ratio of the wing to aerofoil lift curve slopes obtained respectively from ESDU 70011 and ESDU Aero W.01.01.05, thereby accounting for aspect ratio, taper and sweep effects. Finally, part-span factors are applied that depend on the spanwise centre of pressure of the loading due to incidence obtained from ESDU 83040. For double-slotted flaps, the range of parameters for which the method was validated are tabulated and include aspect ratios of 3.7 to 10, taper ratios from 0.3 to 0.5, leading-edge sweep up to 48 degrees, Mach numbers up to 0.2, first element deflections of 12 to 48 degrees and second element of 13 to 30 degrees. For triple-slotted flaps, no experimental data were found but it is anticipated the method will apply equally well. Sketches show the correlation between experimental results drawn from the literature and predicted results; for all results, 89 per cent were correlated within 15 per cent. A worked example illustrates the use of the method.