Definition
Ailerons rigged so that the up-going aileron deflects significantly more than the down-going aileron during a roll input. This unequal deflection is designed to reduce adverse yaw by lowering the drag produced on the inside of the turn relative to the drag produced on the outside.
Plain English
An aileron setup where one side moves up much more than the other side moves down when you turn the control wheel. This uneven movement helps the airplane turn more smoothly by reducing the tendency of the nose to swing the wrong way.
Context Anchor
Seen in discussions of airplane flight controls and how aileron design helps the airplane roll smoothly.
Derivation
Differential' comes from the Latin differentia, meaning 'a difference.' Here it points to the deliberate difference between how far the two ailerons deflect. 'Highly' indicates the difference is large rather than subtle.
Why Pilots Care
Reduces the tendency for the nose to swing opposite the intended turn direction.
Intuition Check
“Differential” does not mean the ailerons are different parts. It means the two ailerons move by different amounts: more upward movement and less downward movement.
Example Sentence 1
Because the trainer has highly differential ailerons, the student noticed the nose stayed closer to the turn direction with only light rudder input.
Example Sentence 2
During preflight, the pilot checked that the highly differential ailerons moved farther upward than downward.