Page 66 - Understanding Flight

CH02_Anderson 7/25/01 8:55 AM Page 53

How Airplanes Fly 53

force on wing force on air
(wt + upwash load) (wt + upwash load)

force on upwash weight of
upwash
load plane

Fig. 2.24. Wing out of ground effect.

force on wing force on air
(wt + upwash load) (wt + upwash load)

force on
upwash
upwash weight of
load plane
ground

Fig. 2.25. Wing in ground effect.

the upwash. To compensate for this increased load, the wing must fly
at a greater angle of attack, and thus a greater induced power. As the
wing approaches the ground, the circulation below the wing is
inhibited. As shown in Figure 2.25, there is a reduction in the upwash
and in the additional loading on the wing caused by the upwash. To
compensate, the angle of attack is reduced and so is the induced
power. The wing becomes more efficient.