The horseshoe vortex
The total vortex system associated with a wing, plus its replacement bound vortex system, forms a complete vortex ring that satisfies all physical laws (see Section 5.2.1). The starting vortex, however, is soon left behind and the trailing pair stretches effectively to infinity as steady flight proceeds. For practical purposes the system consists of the bound vortices and the trailing vortex on either side close to the wing. This three-sided vortex has been called the horseshoe vortex (Fig. 5.3).
Fig. 5.4 The simplified horseshoe vortex
Study of the completely equivalent vortex system is largely confined to investigating wing effects in close proximity to the wing. For estimation of distant phenomena the system is simplified to a single bound vortex and trailing pair, known as the simplified horseshoe vortex (Fig. 5.4). This is dealt with in Section 5.3, before the more involved and complete theoretical treatments of wing aerodynamics.