A fundamental aircraft motion is a banking turn. This
maneuver is used to change the aircraft heading.
Using the Wright
as an example,
the turn is initiated by
warping the wings to
roll, or bank, the aircraft to
one side. On the figure, the aircraft is banked to the right
by lowering the right wing tip and raising the left wing tip,
as viewed from behind the aircraft. The
lift of the wings of the aircraft
is a vector quantity which is always directed perpendicular to the
flight path and perpendicular to the wings generating the lift.
As the aircraft is rolled, the lift vector is tilted in the direction
of the roll. We can break the lift vector into two components. One
component is vertical and opposed to the
which is always directed
towards the center of the earth. The other component is an unopposed side
force which is in the direction of the roll, and perpendicular to the
As long as the aircraft is banked, the side force is a constant, unopposed
force on the aircraft. The resulting motion of the
center of gravity of the aircraft is a
circular arc. When the wings are brought level
by removing the warp, the side force is eliminated
and the aircraft continues to fly in a straight line along a new heading.
Notice that the
is not used to turn the aircraft. The aircraft is turned through the action of
the side component of the lift force. The rudder is used during the turn
to coordinate the turn, i.e. to keep the nose of the aircraft pointed
along the flight path.
If the rudder is not used, one can encounter an
adverse yaw in which the drag on the outer wing pulls the aircraft
nose away from the flight path.
The Wright brothers first encountered adverse yaw on their
which had no rudder. During the winter of 1901, as they designed their 1902
aircraft, they decided to include a fixed rudder. But they found during early
flight tests that the fixed rudder actually made the adverse yaw worse.
Orville decided that the rudder should move to keep the nose pointed along
the flight path. Wilbur suggested connecting the controls
of the rudder to the wing warping to make the pilot's job easier.
- Re-Living the Wright Way
- Beginner's Guide to Aeronautics
- NASA Home Page