An airplane rolls on its longitudinal axis, and yaws on an axis normal to the plane. However, the roll and yaw are not independent of each other. In short, “Roll causes yaw, and yaw causes roll.” An aircraft yaw occurs, without any input from the pilot, when an airplane is banked.
A vertical stabilizer at the tail of an aircraft provides directional stability to the plane and an airplane rudder attached to it delivers positive control over the yaw movements of an aircraft. On the other hand, ailerons attached to the airplane wings provide lateral stability to the aircraft and help the airplane to roll.
Aircraft Yaw as a Consequence of Roll
Aircraft yaw is generally initiated via airplane rudders. However, as an aircraft goes into a roll, it acquires a tendency to yaw into the turn, or towards its lower wing. An aircraft having higher directional stability characteristics would exhibit greater aircraft yaw during the roll. Here is how it happens:
- An aircraft initiates a roll to its left.
- The left aileron (attached to the wing) goes up to produce drag.
- The right aileron moves downward to produce more lift.
- As a consequence of increased drag on the left wing, and increased lift on the right wing, the left wing rolls downward while the right wing rolls upward.
- During this phase (with the left wing down and the right wing up), the right wing travels faster through the air and contributes more to the production of lift.
- This increased lift acts diagonally and is divided into two components. The horizontal component of lift enables an airplane to roll in the desired direction.
- The increased production of lift due to the right wing’s relatively higher airspeed and its aileron in down position induces an aircraft yaw towards the left.
This automatic aircraft yaw is desirable and helps the airplane to turn at a higher rate. It is noteworthy that the primary factor that enables an airplane to turn is the horizontal component of lift however, the aircraft yaw assists the plane during a turn.
Aircraft Yaw Causing Roll
Similar to the automated aircraft yaw effect, a roll is also triggered during the yaw of an airplane. If an airplane were to yaw towards the left using its rudder during straight and level flight:
- The nose of the aircraft would yaw to the left.
- The right wing would be exposed to an increased relative airflow thereby producing more lift.
- The increased lift production would cause it to roll upwards, whereas the left wing would roll downwards.
- This automated roll would therefore induce a bank towards the left.
Aircraft yaw and roll must always be considered together since they fundamentally cause one another. In order to turn efficiently, a pilot must necessarily roll to bank in the desired direction, coordinating the bank with rudder to keep in check the aircraft yaw produced as a consequence.
NASA Glenn Research Center. The Beginner’s Guide to Aeronautics. Accessed on December 12, 2011.
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).
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