Definition
The portion of parasite drag produced by the shape of an airfoil as it moves through the air. Profile drag is the sum of form drag (caused by the airfoil's cross-sectional shape disturbing the airflow) and skin friction drag (caused by air rubbing along the airfoil's surface). It is independent of lift production and exists any time the airfoil is moving through the air.
Plain English
The drag created by the wing's own shape and surface as it pushes through the air -- the resistance you'd feel even if the wing weren't producing any lift.
Context Anchor
Seen in aerodynamics discussions of wings, propeller blades, and rotor blades, especially when comparing different types of drag.
Derivation
From the Latin 'proficere,' meaning 'to draw forward' or 'outline.' A 'profile' is the side view or outline of a shape. Profile drag is literally the drag caused by the profile -- the shape and surface -- of the airfoil itself.
Why Pilots Care
It adds to the total drag that thrust must overcome, directly affecting cruise speed, fuel use, and glide performance.
Intuition Check
Profile drag is not the airplane’s total drag, and “profile” does not mean a pilot’s personal profile or a paperwork record. Here, it means drag tied to the airfoil’s physical shape and surface.
Example Sentence 1
Dirt, dents, and frost on the wings all increase profile drag and hurt cruise performance.
Example Sentence 2
At high airspeeds profile drag rises and becomes the largest part of total drag.