ПОНЯТИЕ КОЭФФИЦИЕНТА ЭЛЛИПТИЧНОСТИ ТРАПЕЦИЕВИДНОГО КРЫЛА И МЕТОД ЕГО ОЦЕНКИ

Abstract

When developing modifications of the transport category aircraft to increase their transport efficiency and economy in many cases, there is a need for profound changes in wing parameters. When such changes are implemented, the problem of the wing layout geometry, and the whole lift system “wing + tail unit assemblies”, inevitably arises. The most important step in the selection of parameters of lifting surfaces is to ensure, during their design, the law of change in circulation spanwise, the maximum approximate distribution of circulation in an elliptical wing, which leads to a minimum value of its inductive resistance for a given lift value.The ratio of the circulation values of the velocity of the elliptical (Ge) and tapered (Gt) wings, the values of which are usually estimated using the known coefficients of the wing shapes, was taken as the elliptic coefficient of the tapered wing:– Ktsh and Kesh – the factors of the tapered wing shape and elliptical wing in plan view, equivalent in lift force, as well as in the span and aspect ratio;– Ksh(hi) – the shape factor of the tapered wing, depending on its taper ratio (hi);– Kesh – the optimal value of the shape factor of a simple tapered wing if the taper ratio is h = 2.857 (according to Karafoli), and Сxi min.The analysis of such dependences showed that the increase in the elliptic coefficient Кe is realized by increasing the number of trapezoids (n), forming the plan of the composite wing, and the geometric twist of their local chords.When using such design solutions, it is possible to increase the value Ken, e, and the numerical evaluation models depend, among other things, on: n – the number of trapeziums that form the wing half-sizes; zn i- the coordinates of the wing kinks in its span; ηn – total narrowing of the wing, formed by n trapeziums. e - the relative angles of the geometric twist of the local chords of the trapezoids forming the plan of the modified wing.The developed models are the scientific basis for the re-assembly of not only an isolated wing, but also the entire lift system “wing + tail unit assemblies” that provide minimal inductive resistance, and should also be used as the basis for constructing longitudinal static stability limits and reducing the trim loss of the modification.