2 Aerodynamics
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the trailing edge (about 1 time of the span). The axis of the vortices is approximately parallel to the direction of the incoming flow (as shown in Figs. 2.43,
2.44, 2.45 and 2.46). Figures 2.47 and 2.48 show the flow field characteristics
and free vortex structure of bats in flight. Figure 2.49 shows the downwash
of the aircraft wake and Fig. 2.50 shows the dissipation of the aircraft wake.
Figure 2.51 shows the wake evolution of a large airliner during landing.
In order to lift the aircraft, when the gravity of the aircraft is fixed, the
lift of the aircraft must reach the gravity. And because the lift is proportional
to the square of the speed, it needs enough flight speed to make the wing
produce the required lift. If the speed is not enough, the lift generated by it
will not be enough to overcome the gravity of the aircraft. Therefore, before
taking off, the aircraft needs to run a distance on the runway that is to make
Fig. 2.43 Formation mechanism of wake vortex
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the trailing edge (about 1 time of the span). The axis of the vortices is approximately parallel to the direction of the incoming flow (as shown in Figs. 2.43,
2.44, 2.45 and 2.46). Figures 2.47 and 2.48 show the flow field characteristics
and free vortex structure of bats in flight. Figure 2.49 shows the downwash
of the aircraft wake and Fig. 2.50 shows the dissipation of the aircraft wake.
Figure 2.51 shows the wake evolution of a large airliner during landing.
In order to lift the aircraft, when the gravity of the aircraft is fixed, the
lift of the aircraft must reach the gravity. And because the lift is proportional
to the square of the speed, it needs enough flight speed to make the wing
produce the required lift. If the speed is not enough, the lift generated by it
will not be enough to overcome the gravity of the aircraft. Therefore, before
taking off, the aircraft needs to run a distance on the runway that is to make
Fig. 2.43 Formation mechanism of wake vortex