Definition
A dimensionless number that expresses how efficiently a wing produces lift at a given angle of attack, in a given configuration, under a given set of airflow conditions. It captures the combined effect of the wing's shape, its angle to the oncoming air, and the surface condition into a single value used in the lift equation: Lift = CL × ½ρV² × S, where ρ is air density, V is airspeed, and S is wing area.
Plain English
A single number that tells you how good a wing is at making lift right now. The number changes mainly with how steeply the wing is tilted into the wind. A higher number means more lift for the same speed and air.
Context Anchor
Seen in aerodynamics, stall, angle-of-attack, flap, and aircraft performance discussions.
Derivation
Coefficient comes from Latin roots meaning 'working together' — a number that works alongside other factors in an equation. So 'coefficient of lift' is the number that works together with speed, air density, and wing area to give you the actual lift.
Why Pilots Care
It directly affects stall speed, takeoff distance, climb performance, and the airspeed at which maximum lift occurs.
Grounding Statement
For the same airplane, CL rises as the wing is asked to make more lift, up to a limit.
Intuition Check
Do not read coefficient of lift as the actual amount of lift in pounds. CL is a comparison number; actual lift also depends on airspeed, air density, and wing area.
Example Sentence 1
As the pilot raised the nose, the angle of attack increased and the coefficient of lift rose with it — until the critical angle was reached and the wing stalled.
Example Sentence 2
During preflight planning the student used the coefficient of lift value to estimate the required takeoff speed at the current density altitude.