Definition
The movement of an aileron up or down from its neutral position when the pilot turns the control wheel or moves the stick sideways. One aileron deflects upward while the opposite aileron deflects downward, changing the lift produced by each wing and causing the airplane to roll.
Plain English
How far the ailerons are tilted away from their flat, resting position. When you turn the yoke, the ailerons move — one goes up, the other goes down — and that movement is the deflection.
Context Anchor
Seen in stall and spin discussions, especially when explaining why pilots are usually taught not to try to pick up a dropped wing with aileron during a stall or spin.
Derivation
Deflection comes from the Latin deflectere, meaning to bend or turn aside. The aileron is being turned aside from its neutral, streamlined position.
Why Pilots Care
Correct aileron deflection is essential for coordinated roll and for avoiding aggravation of spins during recovery.
Intuition Check
Do not read deflection as damage or bending of the wing itself. Here it means normal control-surface movement away from center.
Example Sentence 1
During the stall, the instructor cautioned against large aileron deflection and told the student to use the rudder to keep the wings level.
Example Sentence 2
Full aileron deflection at low speed produces a rapid roll but also increases adverse yaw.