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How It Works
The lift equation L = ½ρv²ACL determines the aerodynamic lift generated by a wing. Lift depends on air density (ρ), airspeed (v), wing area (A), and the lift coefficient (CL). Doubling the airspeed quadruples the lift because lift is proportional to v².
Standard sea-level air density is 1.225 kg/m³. The lift coefficient is a dimensionless number that depends on the airfoil shape and angle of attack.
Example Problem
A small aircraft wing has A = 16 m², CL = 1.2, and flies at 60 m/s at sea level. What lift does it generate?
- L = ½ × 1.225 × 60² × 16 × 1.2
- L = 0.5 × 1.225 × 3,600 × 16 × 1.2 = 42,336 N
That is about 4,318 kgf of lift — enough for a light aircraft.
Frequently Asked Questions
What is a lift coefficient?
The lift coefficient (CL) is a dimensionless number that describes how effectively an airfoil generates lift. It depends on the shape, angle of attack, and Reynolds number. Typical values range from 0 to about 2.0 for conventional airfoils.
Why does lift decrease at high altitude?
Air density decreases with altitude. Since lift is proportional to ρ, an aircraft must fly faster or increase the angle of attack to maintain the same lift at higher altitudes.
How do flaps increase lift?
Flaps increase both the wing area and the lift coefficient by changing the airfoil shape. This allows slower takeoff and landing speeds but also increases drag.
Related Calculators
- Density Calculator — find air density at different conditions.
- Force Equation Calculator — general force calculations.
- Projectile Motion Calculator — analyze flight paths.
- Bernoulli Theorem Calculator — the pressure-velocity relationship behind airfoil lift.
- Speed Unit Converter — convert airspeed between knots, mph, km/h, and m/s.
Reference: Lindeburg, Michael R. 1992. Engineer In Training Reference Manual. Professional Publication, Inc. 8th Edition.