Determining the Aspect Ratio of a wing based on its Mean Aerodynamic Chord

Abstract

The aspect ratio of a wing has its origin in the concept of slenderness, understood as the visual aspect that results from comparing its length with its width, that is, its span between its chord, but considering a rectangular shape, it which, in turn, allows us to obtain the same result by relating the square of the wingspan to its wing surface, the latter being the current convention for calculating the aspect ratio of any wing. This has the disadvantage of not quantifying the effects between different wing shapes. The same spans and areas will give the same aspect ratio regardless of the shapes. Therefore, in this work it is proposed to reconsider the way of calculating aspect ratio, recovering its original concept based on slenderness, using the average aerodynamic chord, which, in its determination, does consider the geometry of each wing. To compare and quantify the differences, a comparative study was conducted with five wings of quite different geometries, for which their aspect ratio, their average aerodynamic chords, their Oswald factors were calculated, their induced drag coefficients and their fine aerodynamics. Results are presented that highlight significant differences when the current convention for aspect ratio is applied and when it is calculated using the average aerodynamic chord suggested here, resulting in differences of up to 7.48% in aerodynamic efficiency or fineness.