Increments in aerofoil lift coefficient at zero angle of attack and in maximum lift coefficient due to deployment of various leading-edge high-lift devices at low speeds.
ESDU 94027 presents an estimation method based on first approximations from the theory for a thin hinged plate modified using empirical correlation factors to account for the geometry of practical aerofoils and high-lift devices. It applies to plain flaps@ drooped leading edges@ slats (including sealed slats) and Krueger flaps (including vented Kruegers). To allow for the effects of chord extension@ the flap chord ratio and lift coefficients are based on an aerofoil extended chord. The data from which the methods were developed were extracted from wind-tunnel tests reported in the literature covering a wide range of practical geometries. However@ the methods for Krueger flaps apply only to those cases in which the flap leading-edge radius is the same as that of the basic aerofoil. The methods apply to Reynolds numbers greater than a million and freestream Mach numbers less than 0.2. The predicted and test data for the lift coefficient decrement at zero angle of attack are correlated to within 0.07 and the increment in maximum lift coefficient to within 0.1. The use of the methods is illustrated by worked examples. To obtain results for an aerofoil with both leading- and trailing-edge devices deployed@ ESDU 84026 is used in conjunction with results from this document and the appropriate document of ESDU 94027 to 94031 for the contribution of trailing-edge devices.