Representing diagrammatically the relative strengths of the cyclic systems as the sides of a parallelogram (Fig. 85), we arrive at an indication of the manner in which the vortices will spread as they are left behind by an aerodrome in flight.
Following the matter further we may represent the interaction of the vortices on each other in the manner shown in plan in Fig. 86. This figure is merely a diagram, the motion indicated being based on the known properties of vortices (§ 93).
Fig. 86. The filaments will evidently wind round one another like the strands
of a rope, being involved in common in the resultant cyclic disturbance. The two vortex trunks springing respectively from the right and left hand wings, owing to their rotation being opposite, do not wind round each other but precess downwards as in Fig. 79. The motion is represented as becoming incoherent in Fig. 86, as undoubtedly must sooner or later be the case.
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