# Airplane Rudders Provide Directional Control in Aircraft

The vertical stabilizer of a Royal Jordanian A319, with the rudder installed at the trialing edge of the vertical stabilizer. Photo Credit: Irfan Jaffry

Certain surfaces capable of interacting with the airflow in a productive manner (airfoils) are installed to control an airplane along the three axes of rotation. For directional control, airplane rudders are used. Directional motion of an aircraft is termed as “yaw.” In order for an aircraft to yaw, the plane must have a surface to initiate and control the yaw movement.

This surface is a typical airfoil installed at the trailing edge of the vertical stabilizer. Airplane rudders function by generating a force and providing for that force as a point of application. In simpler words:

1. Airplane rudders produce an aerodynamic force.
2. This aerodynamic force acts from the rudder surface.
3. The applied force creates a movement and the aircraft yaws to the intended direction.

### How Airplane Rudders Work?

Airplane rudders, installed at the trailing edge of the vertical stabilizer, move either left or right to create the desired aerodynamic force. The creation of this force is similar to the production of lift by the aircraft wings. Rudders function in the following manner:

1. When in flight, if the rudder is made to move towards the left, the airflow around the vertical stabilizer is affected.

The massive vetical stabilizer of an Airbus A380, attached to which is the airplane rudder. Photo Credit: Motohide Miwa

2. The now-left rudder is exposed to a sideways angle of attack.
3. Static pressure on the left side of the rudder is increased while that on the right side is decreased.
4. The region of decreased static pressure on the right side pulls the vertical stabilizer towards the right.
5. This pull is basically an aerodynamic force generated by the pressure differential between the left and right side of the rudder.
6. This aerodynamic force acts via the rudder.
7. A moment is created and the aircraft rotates over its center of gravity.
8. The tail of the aircraft moves right, while the nose yaws to the left.
9. Left deflection of the rudder yaws the plane to the left.

The effective functionality of airplane rudders is directly proportional to its immediate airflow. The higher the speed of air flowing around the rudder, the higher would be its efficiency. Hence, aircraft have effective directional control at higher airspeeds. Similarly, propeller slipstream over the rudder would also increase its efficiency.

The following video explains the concept of yawing and how airplane rudders influence movement in this plane.

Resources

Federal Aviation Administration, Flight standards Service. Airplane Flying Handbook. (2004).

Federal Aviation Administration, Flight standards Service. Pilot’s Handbook of Aeronautical Knowledge. (2008).

Trevor, T. Aeroplane General Knowledge and Aerodynamics. Aviation Theory Centre. (2004).