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CH03_Anderson 7/25/01 8:56 AM Page 83

Wings 83

Fig. 3.22. Laminar flow turning into turbulent flow when passing through a
plate with holes. (Photo courtesy of Thomas Corke and Hassan Nagib.)

tendency of a laminar boundary layer to become turbulent, things
such as rivets, bugs, and raindrops can trigger boundary-layer
turbulence. A great deal of effort has gone into understanding
boundary-layer turbulence and devising ways to reduce or eliminate
it. Modern wings attempt to maintain laminar flow as far back on the
wing as possible but transition to turbulence before the air has a
chance to separate. If you look at the wing of a jet, you will see that it
is smooth part of the way back and then there is less concern for
smoothness.
A popular home-built airplane
Turbulence does have one beneficial effect. Because the
has had problems flying in rain.
airflow in the boundary layer is churning, it mixes the most
The Vari-EZ and Long-EZ, shown
energetic air with air close to the wing surface. Thus the
in Figure 3.19, have laminar-flow
boundary layer is energized and has increased kinetic energy.
canards. When flown in rain, the
The advantage of this is that the air will stay attached to the
water droplets ruined the
surface longer. A laminar-flow wing will stall at a lower
laminar-flow properties. The
angle of attack than a wing with turbulent flow. Another
aerodynamic changes seen by
method for energizing the boundary layer is to add vortex
the canard were sufficient for
generators. Many airplanes use vortex generators to delay
pilots to notice changes in the
separation of the air, and thus delay stall. Vortex generators
handling characteristics.
are discussed below.