Definition
A number that expresses how much lift a wing produces for a given angle of attack, wing shape, and flap configuration, at a given airspeed and air density. A higher lift coefficient means the wing is producing more lift for the same airspeed and air density. The lift coefficient changes with angle of attack and with the use of high-lift devices such as flaps and slats.
Plain English
A number that describes how good the wing is at making lift in its current shape and position. Raise the nose or lower the flaps and the number goes up. Stall the wing and the number drops sharply.
Context Anchor
Seen when studying how flaps let an airplane produce more lift during takeoff, approach, and landing.
Derivation
Coefficient comes from Latin co- (together) and efficere (to bring about). In math and physics, a coefficient is a number that scales another quantity. Here it scales the basic lift equation, telling you how effective the wing is at turning airspeed and air density into lift.
Why Pilots Care
Flap extension raises the wing's lift coefficient, allowing slower flight speeds before stall and shorter takeoff and landing distances.
Grounding Statement
When flaps go down, the wing changes shape and can make more lift at a slower speed.
Intuition Check
Do not read “lift coefficient” as the actual amount of lift in pounds. It is a comparison number that shows how strongly the wing is producing lift under those conditions.
Example Sentence 1
Lowering the flaps increases the wing's lift coefficient, which is why the airplane can maintain flight at a slower approach speed.
Example Sentence 2
Knowing the maximum wing's lift coefficient helps the pilot calculate the stall speed for the current flap setting.