Definition
A dimensionless number that represents the amount of drag produced by a body moving through a fluid, accounting for the shape of the body and its angle relative to the airflow. It is used in the drag equation to calculate total drag force, where drag equals the coefficient of drag multiplied by dynamic pressure and reference area.
Plain English
A single number that captures how much an object resists moving through the air based on its shape and how it is angled. A streamlined wing has a low number; a flat plate held face-on has a high one.
Context Anchor
Seen in aerodynamics, aircraft performance, and discussions of how flaps, landing gear, or aircraft shape affect drag.
Derivation
Coefficient comes from Latin meaning 'working together' — a number that works together with other values in a formula. Drag is the rearward force resisting motion through air. Together: a number that, combined with speed and size, gives you the drag force.
Why Pilots Care
Directly affects required thrust, fuel burn, and maximum speed; a lower value improves efficiency and range.
Analogy
Think of it as a slipperiness number for air. A clean, smooth shape has a lower number; a bulky or dirty shape has a higher number.
Grounding Statement
A smaller coefficient of drag means the airplane needs less power to maintain the same speed.
Intuition Check
Coefficient of drag is not the drag force itself. It is the number that describes how strongly a shape or aircraft setup tends to create drag.
Example Sentence 1
As the pilot increased the angle of attack, the coefficient of drag rose steeply, and the airplane required more power to maintain altitude.
Example Sentence 2
Adding wheel fairings lowered the coefficient of drag and increased the airplane's cruise speed by several knots.