Secondary Effects of Controls

Primary vs Secondary Effects

Each control surface is designed for a primary effect:

• Ailerons: Roll (longitudinal axis)
• Elevator: Pitch (lateral axis)
• Rudder: Yaw (vertical axis)

However, moving a control surface almost always causes at least one secondary effect due to aerodynamic interactions and changes in airflow.

Aileron Secondary Effects

When you deflect the ailerons, the aircraft rolls, but the downward-moving aileron increases lift and drag on that wing. The increased drag causes the nose to yaw in the opposite direction of the roll—this is adverse yaw. Pilots must use coordinated rudder input to counteract this yaw and maintain balanced flight.

Rudder Secondary Effects

Applying rudder primarily yaws the aircraft, but this also causes the outer wing (in the direction of the yaw) to move faster, generating more lift and causing the aircraft to roll in the same direction as the yaw. To keep the wings level during rudder input, opposite aileron may be needed.

Elevator Secondary Effects

Elevator input mainly changes pitch, with negligible secondary effects under normal conditions. However, at high angles of attack or low speeds, elevator-induced pitch changes can alter airflow over the wings and tail, potentially affecting stability and control.

Operational Importance

Secondary effects become more pronounced at low speeds and high angles of attack, where control effectiveness is reduced and larger control inputs are needed. Pilots must anticipate and counteract these effects to avoid uncoordinated flight, especially during take-off, landing, and slow flight.