Abstract:

ESDU 87005 gives a simple method for predicting the increment in drag at zero incidence for a flap positioned to maximise lift at stall. Using the limited number of experimental data available in the literature, a correlation method was developed that leads to a carpet graph of the variation of the increment with flap deflection angle and the ratio of the extended chord (due to flap deployment) to the basic aerofoil chord (with flap retracted). The carpet applies to aerofoils with maximum camber position between 0.2 and 0.65 of chord, and predicts the drag increment to within 20 per cent. The position of maximum camber was found to have a significant effect, and two similar carpets, one for maximum camber at 0.15 chord and one for it positioned between 0.7 and 0.8 of chord illustrate the trends with aerofoil and flap deployment geometry. The range of geometries for which experimental data were available and used to test the method is given. The method does not apply if any leading-edge device is also deployed. A worked example illustrates the use of the method. A Fortran program of the method is provided as ESDUpac A8705.