Lift is the key aerodynamic force in flight. According to Newton's Third Law, every action has an equal and opposite reaction. Lift opposes weight and enables flight in birds, airplanes and other objects. The coefficient of lift (Cl) measures lift as it relates to the angle between the shape of a wing and the direction of the wind. This angle increases as Cl increases until reaching a peak, at which point lift is quickly lost and a wing stalls. The lift equation can be used to calculate how much weight a given wing can carry.
How to Calculate Lift Coefficient
Determine the object's velocity (V) in miles per hour, density (r) in pounds per square inch, wing area (A) in feet squared and the amount of lift (L) in pounds.
Calculate the dynamic pressure, which equals one half the density multiplied by the velocity squared, or q = .5 * r * V^2.
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Divide the lift by the dynamic pressure multiplied by the wing area. In other words, Cl = L / (q * A). This expresses the coefficient of lift.
You can measure Cl mathematically at slow speeds under sea level conditions using the equation 2 times pi (3.14159) multiplied by the angle between the mid-line of the wing and the relative wind. However, Cl is typically determined through wind tunnel tests where the velocity, density and area can be controlled.