Secondary Effects of Controls

When a primary control is operated, unwanted or additional effects also occur. The pilot must know and compensate these secondary effects.

Aileron — secondary effects

Adverse yaw

Main secondary effect (see separate lesson).
Cause: unequal drag left/right on aileron deflection.
Result: yaw opposite to roll direction.
Compensation: rudder in roll direction.

Roll secondary effect via bank

Bank → lift vector tilts → slip downward → lift component against gravity decreases → altitude loss.
Compensation: pitch-up (yoke slightly back) during turn.

Elevator — secondary effects

Speed change

Pitch-up → α rises → CL rises → more induced drag → speed drops.
Pitch-down → α drops → CD drops → speed rises.
Mantra: "Pitch for speed, power for altitude" (in climb/descent/approach).

Bank effect in turn

Pitch-up in turn: lift rises → vertical component maintains altitude, but horizontal component (centripetal) also rises → turn tightens (turn rate rises, radius drops).
Important in steep turns (>30° bank).

Rudder — secondary effects

Roll via dihedral

Yaw induces sideslip.
Sideslip induces via dihedral (see lesson "Lateral Stability") a roll moment.
Result: rudder alone produces roll in the same direction (left pedal → slight roll left).
Strength: depends on dihedral and wing position.
In trainers like PA-28 (5° dihedral): clearly noticeable.

Pitch effect

Small: rudder produces some lift sideways at tail → pitching moment.
In normal GA practically negligible.

Speed loss via rudder

Heavy rudder deflection: produces extra drag → speed drops.
Avoid in cruise.

When both controls used at once

Coordinated turn

Aileron + rudder together:

Aileron initiates roll.
Rudder compensates adverse yaw.
Elevator maintains altitude.
Ball in slip indicator centred.

Slip

Aileron + opposite rudder:

More aileron than needed for bank.
Rudder prevents yaw → aircraft flies skewed (nose not in motion direction).
Ball moves to the bank side (aileron side).
Use: crosswind landing (see Subject 070), rapid descent without speed gain.

Skid

More rudder than for coordinated turn:

Aircraft "slides" outside the turn direction.
Ball moves opposite to the bank side.
Very dangerous: can lead to stall-spin.
Classic accident: base-to-final approach with skidding turn → uncoordinated stall → spin.

Operational consequences

Approach mantra

Maintain coordinated flight: ball centred.
Compensate adverse yaw: rudder with aileron coordinated.
Avoid skids: too much rudder can be fatal at low speed.

Cruise mantra

Small inputs: less secondary-effect compensation needed.
Set trim: aircraft flies nearly itself.

Exercises for secondary-effect awareness

Aileron-only: roll aircraft without rudder — feel adverse yaw.
Rudder-only: pedals without yoke — feel roll via dihedral.
Coordinated turns: 30°/45° bank with ball centred.
Slip/skid demo: deliberately initiate slip or skid and feel effect.

These exercises are standard in the PPL skill test (FCL.235).