IHS ESDU Effect of geometry on low speed pitch-break characteristics of swept wings. 01005

ESDU 01005 provides a means of predicting the type of pitch-break likely to be encountered for a given wing planform shape at low speeds. The method has been developed for wings alone and wing-body configurations and is based on an analysis of a large quantity of experimental data. Either pitch-up or pitch-down can occur depending mainly on planform shape through its influence on the flow field. It was found that characterising the planform by the parameter A tan alpha, where A is aspect ratio and alpha is quarter-chord sweep, was adequate to define the type of pitch-break. For A tan alpha less than 2.6 pitch-down occurred while for A tan alpha greater than 3 pitch-up occurred, with either type of break being possible for values in between. Where a planform has varying amounts of sweep across each semi-span, ESDU 76003 is used to define an 'equivalent' straight-tapered wing. The values of the geometric parameters defining the range of planform shapes for which data were available are tabulated and show that the method applies to a wide range of wing planforms, including swept-forward geometries. Its high reliability is illustrated by sketches showing all the data on plots of A versus tan alpha. Two fully worked examples illustrate the use of the method.