Definition
A dimensionless number that expresses how effectively an airfoil produces lift at a given angle of attack, in given flow conditions. It is used in the lift equation along with air density, velocity squared, and wing area to calculate the total lift force produced by a wing.
Plain English
A number that tells you how good a wing is at producing lift at a particular angle to the oncoming air. The higher the number, the more lift the wing is generating for the same speed and air density.
Context Anchor
Seen in aerodynamics, wing performance, stall discussions, flap discussions, and aircraft performance calculations.
Derivation
Lift comes from Old Norse 'lypta', meaning to raise. Coefficient comes from Latin 'co-' (together) and 'efficere' (to bring about) — literally a number that works together with other factors to produce a result. In the lift equation, the coefficient is the factor that ties the wing's shape and angle to the lift it produces.
Why Pilots Care
It governs how much lift a wing can produce before stalling and directly affects takeoff, landing, and maneuvering distances.
Analogy
It is like an efficiency rating for the wing. Two wings may be moving through the same air at the same speed, but the one with the higher lift coefficient is producing more lift for those conditions.
Grounding Statement
Picture the same airplane at the same speed: if the pilot changes the wing’s angle or extends flaps, the lift coefficient changes even though the wing size has not.
Intuition Check
Do not read lift coefficient as the total amount of lift. It is a comparison number that describes how strongly the wing is producing lift under the current conditions.
Example Sentence 1
As the pilot increased the angle of attack on final approach, the lift coefficient rose, allowing the aircraft to maintain flight at a lower airspeed.
Example Sentence 2
Flaps increase the wing's maximum lift coefficient, allowing slower approach speeds.