Page 18 - Understanding Flight

CH01_Anderson PFS2 7/25/01 8:55 AM Page 5

Basic Concepts 5

A useful measure of a wing is its aspect ratio. The aspect The Boeing B-314 Flying Boats
ratio is defined as the wing’s span divided by the average or were so large that there was a
mean chord length. The span is the length of the wing catwalk in the wings so the
measured from wingtip to wingtip. The mean chord length is mechanics could service the
the average chord length along the wing. The area of the wing engines in flight.
is just the span times the mean chord length. Most wings on
small general-aviation airplanes have aspect ratios of about 6 to 8.
This means that the wing is 6 to 8 times longer than its average width.

Axes of Control
An airplane moves in three dimensions called roll, pitch, and yaw,
illustrated in Figure 1.5. Roll is rotation about the longitudinal axis that
goes down the center of the fuselage. The ailerons control rotation
about the roll axis. Pitch is rotation about the lateral axis of rotation,
which is an axis parallel to the long dimension of the wings. The ele-
vators control the pitch of the airplane. By controlling the pitch of the
airplane, the elevators also control the angle of attack of the wing. To
increase the angle of attack, the entire airplane is rotated up. As we
will see, this control or the angle of attack is key in the adjustment of

Yaw axis
(vertical axis)

Roll axis
(longitudinal axis)
Pitch axis
(lateral axis)
Fig. 1.5. Axis of rotation of an airplane.