Stability and control are much
more complex for an airplane, which can move freely in three dimensions, than
for cars or boats, which only move in two. A change in any one of the three
types of motion affects the other two.
Imagine three lines running
through an airplane and intersecting at right angles at the airplane’s center of gravity.
● Rotation around the front-to-back axis is
called roll.
● Rotation around the side-to-side axis is
called pitch.
● Rotation around the vertical axis is
called yaw.
● The Ailerons Control Roll
● On the outer rear edge of each wing, the
two ailerons move in opposite directions, up and down, decreasing lift on one
wing while increasing it on the other. This causes the airplane to roll to the
left or right. To turn the airplane, the pilot uses the ailerons to tilt the
wings in the desired direction.
● The Elevator Controls Pitch
● On the horizontal tail surface, the
elevator tilts up or down, decreasing or increasing lift on the tail. This
tilts the nose of the airplane up and down.
● The Rudder Controls Yaw
● On the vertical tail fin, the rudder
swivels from side to side, pushing the tail in a left or right direction. A
pilot usually uses the rudder along with the ailerons to turn the airplane.