by Jonathan M. Stern
Primary Flight Controls
The airplane is controllable around three axes—the yaw axis, the pitch axis, and the roll axis. The rudder moves the airplane about its yaw axis (see Figure 2.3).
Figure 2.3. The arrow points to the rudder, which, while deflected to the left, causes the airplane to yaw to the left.
The elevator moves the airplane about its pitch axis. And the ailerons move the airplane about its roll axis.
The elevator is manipulated by fore and aft movement of the control yoke (the airplane's equivalent of a steering wheel) while the rudder is manipulated by pressing on the rudder pedals (see Figure 2.4).
Figure 2.4. The ailerons and elevator are controlled with the yoke while the rudder is manipulated with the rudder pedals.
The rudder causes the airplane to yaw left or right. The control yoke is connected to the ailerons and elevator through a series of cables and bell cranks or, in some airplanes, through metal tubes. When the control yoke is pulled aft (toward the pilot), the trailing edge of the elevator moves upward (see Figure 2.5).
Figure 2.5. With sufficient airspeed, the up elevator causes the nose to pitch up.
This causes the empennage to move downward and, accordingly, the nose of the airplane to move upward. Assuming sufficient speed and control movement, aft movement of the control yoke causes the airplane to climb while forward movement of the control yoke causes the airplane to descend.
The ailerons, hinged on the trailing outboard edge of each wing, move in the opposite direction of one another (see Figure 2.6).
Figure 2.6. When the right aileron is lowered (as pointed out by the arrow), the left aileron is raised.
When the control yoke is rotated counterclockwise, the left aileron moves up and the right down. The lowered aileron produces more lift than the raised aileron, causing the airplane to bank to the left. When the control yoke is rotated clockwise, the right aileron moves up and the left down.
The ailerons are the controls primarily responsible for making the airplane turn. The rudder is used in a turn solely to overcome what is known as adverse aileron yaw, explained in the next sections.