Page 84 - Understanding Flight

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Wings 71

root stalls. If the tip stalled first, the pilot would lose roll con- Philanthropist Daniel Guggenheim
trol during the stall. This could lead to an uncontrolled stall- was an aviation enthusiast. The
spin. If wings are designed such that the root stalls first, the Daniel Guggenheim Fund
pilot can control the airplane and prevent the spin. established seven aeronautical
Though mechanically twisting the wing is common on schools in the late 1920s. These
general-aviation aircraft, commercial transports and other high- were MIT, Caltech, University of
performance airplanes use an aerodynamic twist. Aerodynamic Michigan, NYU, Stanford, Georgia
twist results when the wing sections are changed from root to tip. School of Technology (now
In other words, different wing section designs are selected for Georgia Tech), and the University
different positions along the span of the wing. For example, a of Washington. Of the seven
designer might reduce the camber of the wing sections from root original, only NYU no longer has
to tip. The goal is to select a wing that is more lightly loaded at a program in aeronautics.
the tip and will not stall at the same angle that the wing root
stalls. The result is that the wing behaves as though it is twisted,
although it is twisted aerodynamically and not mechanically.

Wing Configuration

There is still more to a wing than its airfoil and planform. The config-
uration of the wing, as viewed from the front, can affect stability, effi-
ciency, and practicality. Why are wings sometimes slanted up or down
from the root to the wingtip? Should the airplane have a low wing, a
high wing, or a midwing? What type of wingtip is best? When should
one consider a biplane?

Dihedral
Roll and yaw stability are desirable characteristics for trainers and trans-
ports, both of which can be enhanced by adding dihedral to the wings.
Dihedral is the upward angle of the wing along the span against the
horizon, as shown in Figure 3.14. Many are taught that the reason dihe-
dral adds stability is that as the airplane rolls gravity pulls the
Manfred Von Richthofen (the Red
upward wing back to horizontal. Unfortunately, the truth is
Baron) flew the Fokker triplane,
more complex.
for which he is famous, for only
When an airplane enters a roll, there is a tendency to yaw
6 weeks and 19 of his 80
in the opposite direction. For example, if the airplane rolls to
victories.
the right, it is accompanied by a yaw to the left. That is, the