Page 64 - Understanding Flight

CH02_Anderson 7/25/01 8:55 AM Page 51

How Airplanes Fly 51

cause of upwash. When an airplane is traveling at Mach 1 or faster,
information cannot communicate forward and the wing has no
upwash. But at the speed common for small airplanes, upwash is
quite pronounced. If Figure 2.22 were expanded so more of the air
could be seen, one would see that the air is going almost straight
down far behind the wing, and that the effect of the wing extends far
above the wing.
Something to notice in the simulations of circulation is that there is
very little action below the wing. Most of the work is being done
above the wing. This is why the bottom side of military aircraft can be
so cluttered with munitions and fuel tanks, as in the F-16 fighter
shown in Figure 2.23. These obstructions cause an increase in
parasitic power but do little to affect the efficiency of the wing. The
top of the wing is a different story. Obstructions above the wing
interfere with lift. This explains why struts are common on the bottom
of wings but are historically rare on the top of the wing.

Flight of Insects

Statements have been made that classical aerodynamic
theory proves that insects cannot fly. In all cases that we are
familiar with, the flight of insects is expressed in terms of
circulation. Circulation is a model developed for large
aircraft that does not apply to small insects, by blowing air
down. Insects obey the same laws of physics as airplanes.
Insects produce lift just like airplanes, by blowing air down.
When you have a chance, observe a bumblebee feeding on
flowers.You will see that when it flies over a leaf on the
plant, the leaf is depressed just as if it had landed on it. It
clearly is producing lift the same way an airplane does.

Ground Effect
Insects produce lift just like
The concept of circulation is necessary for the understanding of
airplanes, by blowing air down.
ground effect. This effect is the increase in efficiency of a wing as it