Page 61 - Understanding Flight

CH02_Anderson 7/25/01 8:55 AM Page 48

48 CHAPTER TWO

X
Heavy loading

Light loading X
Fig. 2.20. The effect of wing loading on the airflow behind a wing.

lower load. The tightness of the bend reflects the rate of change in the
load along the wing. At the end of the wing the lift goes to zero very
rapidly and there is some airflow around the wingtip. This causes the
tightest curl in the wing vortex, creating the wingtip vortex. The
details of the wing vortex can be clearly seen in Figure 2.7 of a jet
flying over fog. The center of the trough formed by the downwash
sheet has smooth sides terminating in the tight curl of the
wingtip vortex.
At the end of the wing the lift
The wingtip is usually the place on the wing with the
goes to zero very rapidly,
greatest change in lift and thus produces the most visible
causing the tightest curl in the
vortex. This is not always at the wingtip. Figure 2.21 shows a
wing vortex and creating the
landing airplane producing flap vortices. In this example the
wingtip vortex.
change in lift is greatest at the outer edge of the wing’s flap.

Circulation

As mentioned before, circulation is a measure of the rotation of the air
around the wing, when seen from the rest frame where the air is ini-
tially standing still and the wing is moving. Circulation has been mis-