Taper and shape of wing tips

In addition to changes of aspect ratio, the plan form of the wing may be tapered from centre to wing tip; this is often accompanied by a taper in the depth of the aerofoil section (Fig. 3.31) and also by a ‘wash-out’, or decrease of angle of incidence, towards the wing tip – sometimes too a different aero­foil section is used near the tips. The tapered wing has advantages both from the structural and aerodynamic points of view. This is a feature in which we were slow to accept the teachings of nature, for the wings of most birds have a decided taper. Where the chord is not constant along the span, the numer­ical value of the aspect ratio is usually taken as the fraction (span/mean chord), or span2/area.

Taper in plan form means a sweepback of the leading edge, or a sweepfor – ward of the trailing edge, or both. Considerable sweepback of the whole wing

is sometimes used, but this is usually more for consideration of stability or for very high-speed flight, and discussion of the problem from these points of view is deferred to later chapters.