Function
An airplane rudder controls the yaw, or side to side motion, of an aircraft.
Misconceptions
Unlike the rudder on a ship, the rudder of an airplane is not the primary control surface involved in making a turn. The airplane rudder counteracts adverse yaw when making a turn or p-factor, a force that pulls the airplane to one side when the propeller is at a high angle of attack (such as takeoff and climbing).
Benefits
Use of the rudder aids the pilot in changing the direction of the airplane. If the pilot only used the aerilons to roll the airplane along the vertical axis the airplane.
Coordinating a Turn
A coordinated (non-slipping or skidding) turn in an airplane uses aerilons that roll, or bank, the airplane and the rudder to point the nose in the direction of the turn. Cockpit instruments provide a visual cue to the pilot when the airplane is slipping or skidding by way of a ball that is pushed or pulled out of center.
Using the Rudder
When the indicator ball in the turn coordinator instrument is not centered the pilot can depress the rudder pedal on the floor on the same side to which the ball has moved.
Warning
Excessive application of the rudder can result in a spin that can cause the airplane to lose altitude rapidly.