Horseshoe vortex

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The horseshoe vortex model is a simplified representation of the vortex system of a wing. In this model the wing vorticity is modelled by a bound vortex of constant circulation, travelling with the wing, and two trailing vortices. (Any starting vortex initially created is considered to have been dissipated, as are the trailing vortices well behind the aircraft.). The trailing vortices are resposible for the downwash which creates induced drag.

The model is very unrealistic in implying a constant vorticity (and hence by the Kutta-Joukowski theorem constant lift) at all points on the span. In a more realistic model (due to Ludwig Prandtl) the vortex strength reduces along the span, and the loss in vortex strength is shed as a vortex-sheet from the trailing edge, rather than just at the wing-tips. However, by using the model with a reduced effective span but same midplane circulation, the flows induced far from the aircraft can be adequately modelled.