# Lift Force

on . Posted in Fluid Dynamics

Lift force, abbreviated as L, also called lift, for an body moving through a fluid (gas or liquid) or air, is the force exerted perpendicular to the direction of travel.  It's a fundamental aerodynamic phenomenon that describes the force exerted on an object (such as an aircraft wing or a rotor blade) perpendicular to the direction of an oncoming fluid flow, typically air.  Lift is what allows aircraft to generate upward motion and counteract the force of gravity.

Lift is primarily generated due to differences in air pressure on the upper and lower surfaces of a wing or airfoil.  When an airfoil moves through the air at a non-zero angle of attack (the angle between the chord line of the airfoil and the oncoming airflow), it causes the air to flow over and under the airfoil, creating different pressure distributions.

The Bernoulli's principle, which relates the speed of a fluid flow to its pressure, helps explain the lift generation.  As the air moves faster over the curved upper surface of the airfoil, its pressure decreases.  Meanwhile, the slower-moving air beneath the airfoil has higher pressure.  This pressure difference results in an upward force, perpendicular to the direction of the airflow, known as lift.

Key factors that influence lift include the shape of the airfoil, the angle of attack, the speed of the airflow, the density of the air, and the wing area.  Engineers and designers carefully consider these factors to optimize the lift-to-drag ratio and achieve desired aircraft performance.

Lift is crucial for aircraft to become airborne and stay aloft.  However, it's important to note that lift is just one component of the aerodynamic forces at play.  Another significant force is drag, which opposes the aircraft's forward motion through the air.  Balancing lift and drag is essential for achieving efficient and stable flight.

### Lift Force formula

$$L = \frac{1}{2} \; C_l \; \rho \; v^2 \; A$$     (Lift Force)

$$C_l = 2 \; L \;/\; \rho \; v^2 \; A$$

$$\rho = L \;/\; 2$$

$$v = \sqrt{ 2 \; L \; ( 1 \;/\; C_l \; \rho \; A ) }$$

$$A = 2 \; L \;/\; C_l \; \rho \; v^2$$

Symbol English Metric
$$L$$ = lift force $$lbf$$ $$N$$
$$C_l$$ = lift coefficient $$dimensionless$$
$$\rho$$  (Greek symbol rho) = density  $$lbm \;/\; ft^3$$ $$kg \;/\; m^3$$
$$v$$ = velocity $$ft \;/\; sec$$ $$m \;/\; s$$
$$A$$ = area $$ft^2$$ $$m^2$$

Tags: Pressure Force Air