lyftkraft

Lyftkraft is the aerodynamic force that acts on an object moving through a fluid, directed perpendicular to the relative flow. In aviation and other wind-driven systems, lift counters gravity and enables sustained flight for airplanes and rotorcraft, and contributes to propulsion effects on sails.

The magnitude of lift is commonly expressed as L = 1/2 ρ v^2 S C_L, where ρ is fluid density, v is the relative velocity between the object and the fluid, S is the reference area (such as wing area), and C_L is the lift coefficient, which depends on surface shape, angle of attack, Reynolds number, and surface roughness.

Lift is generated primarily by pressure differences between the upper and lower surfaces of a wing or airfoil, as well as by the reaction forces on rotor blades or sails that push the fluid backward. The lift coefficient generally increases with angle of attack up to a critical point where stall occurs, after which lift declines. Designers modulate lift through wing geometry (camber, aspect ratio), surface smoothness, and control surfaces; rotorcraft adjust lift with blade pitch; sails generate lift with sail shape and apparent wind.

In practice, lift must be balanced by weight, drag, and thrust to determine flight performance. The concept is foundational in aerodynamics and is taught alongside related forces such as drag and propulsion.

Etymology: lyftkraft derives from Swedish lyfta (to lift) and kraft (force). In other languages, the term for lift uses different words, but the physical concept remains the same.