løfteforhold

Løfteforhold is a term used in aerodynamics to describe the lift-to-weight ratio of an object moving through a fluid. It indicates how much lifting force generated by the fluid flow compares with the object's weight, and it is a central parameter for assessing flight capability and performance in aviation and related fields.

In practical terms, the lifting force (lift) L is often expressed as L = q S C_L, where q is the dynamic pressure (q = 0.5 ρ v^2), ρ is air density, v is velocity, S is the planform area (wing area), and C_L is the lift coefficient, which depends on the angle of attack and wing geometry. The weight W equals m g, with m the mass and g the acceleration due to gravity. The løfteforhold is L/W. For level flight, L ≈ W, so L/W ≈ 1. A løfteforhold greater than 1 allows climb, while a løfteforhold less than 1 leads to descent.

Factors influencingløfteforhold include air density (which decreases with altitude), velocity, wing area, and the lift coefficient determined by wing design and configuration. High-lift devices such as flaps and slats increase C_L at given speeds, improving the løfteforhold. Aircraft performance calculations routinely use this ratio to determine takeoff and landing performance, rate of climb, and required thrust or power margins. While related concepts include lift coefficient and lift-to-drag ratio, the løfteforhold focuses on the balance between lifting force and weight under prevailing flight conditions.