Lift is the component of aerodynamic force acting perpendicular to the direction of flight. It is produced by pressure differences between the upper and lower surfaces of a wing: air accelerates over the curved upper surface, reducing static pressure (per Bernoulli’s principle), while the lower surface experiences higher pressure. The net upward force is lift.
The more complete explanation is circulation-based: a wing deflects the oncoming airflow downward (the “downwash”), and by Newton’s third law, the air pushes the wing upward. The Kutta-Joukowski theorem formalizes this — lift per unit span equals air density × freestream velocity × circulation around the wing section. The Bernoulli and circulation explanations are not competing theories; they are two descriptions of the same physics.
Lift is calculated as:
L = ½ × ρ × V² × S × C_L
where ρ is air density, V is airspeed, S is wing planform area, and C_L is the lift coefficient (a dimensionless number determined by angle of attack, airfoil shape, and Reynolds number).
For level flight, lift must equal weight. This relationship is the starting point for all wing sizing: given a target gross weight and cruise speed, the required wing area follows directly from the achievable lift coefficient. Wing loading (weight/area) is the ratio that captures this relationship.
The lift equation reveals two ways to increase lift: increase speed (lift scales with V²) or increase the lift coefficient (by increasing angle of attack or deploying high-lift devices). Both have limits — speed is constrained by available thrust, and C_L is bounded by stall. The maximum lift coefficient an airfoil can sustain before stalling determines the minimum speed at which the aircraft can fly at a given wing loading — this is the stall speed, and it sets the lower bound of the flight envelope.
For UAVs, the practical consequence is that a heavier aircraft (higher wing loading) must fly faster to generate enough lift, which increases drag, which increases power consumption, which reduces endurance. Every gram of structural weight that could have been saved translates directly into reduced mission capability through this chain of dependencies.
Related terms
- Drag — the aerodynamic force component parallel to flight direction; the cost of producing lift
- Angle of Attack — the primary variable controlling lift coefficient
- Stall — the condition where increasing angle of attack ceases to increase lift
- Wing Loading — weight per unit wing area, governing the lift coefficient required for flight
- Airfoil — the cross-sectional shape that determines how efficiently lift is produced