Definition
An unequal amount of aerodynamic drag produced by the two wings of an airplane during a roll, caused primarily by the difference in lift each wing is generating. The wing producing more lift also produces more induced drag, which yaws the aircraft toward that wing — the source of adverse yaw.
Plain English
When you roll the airplane, one wing creates more drag than the other. That uneven drag pulls the nose sideways, opposite the direction you are trying to turn.
Context Anchor
Seen in discussions of adverse yaw and aileron use during turns.
Derivation
‘Differential’ comes from the Latin differentia, meaning ‘a difference.’ Here it simply means the drag on the two wings is different, not equal — one wing has more, the other has less.
Why Pilots Care
Recognizing differential drag explains why rudder must be applied with aileron to keep the turn coordinated and avoid slipping or skidding.
Analogy
It is like paddling one side of a canoe harder than the other: the extra resistance swings the front of the boat off course.
Grounding Statement
Picture the right wing being held back slightly more than the left wing; the airplane will tend to swing its nose toward the side with more drag.
Intuition Check
Differential drag does not mean “extra drag everywhere.” It means drag is unequal from one side or part of the aircraft to another.
Example Sentence 1
When the pilot rolled into a left turn, differential drag yawed the nose briefly to the right until rudder was applied to coordinate the turn.
Example Sentence 2
The pilot adds right rudder to cancel the differential drag and keep the turn coordinated.