Calculate lift force from airspeed, wing area, air density, and lift coefficient, or solve for any variable, with altitude density and level-flight checks.
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Lift Force Formula
The following formula calculates signed lift perpendicular to the relative flow. The optional dry-air model uses standard pressure over −500 to 25,000 m geopotential altitude, with temperature lapse layers at 11 and 20 km; blank temperature uses the model temperature. Entered air temperature changes density at that standard pressure, not a prediction of actual weather. The −500 to 0 m segment extends the lowest standard layer. A separate maximum lift coefficient is required for an optional idealized stall-speed comparison.
- Where FL is the force due to lift
- A is the reference area used to define the lift coefficient; Cl is the signed dimensionless lift coefficient
- d is the density of the air
- V is the velocity of the wing through the air
Lift Force Definition
A lift force is a force that is exerted on an object that is moving through a fluid. As the object moves through the fluid, two components of force arise.
One of these is parallel and opposite to the flow of the object. This is known as a drag force. This force will force the object to slow down.
The other component of force is one that is perpendicular to the flow of the object. This component is known as the lift force.
Lift is the net force perpendicular to the relative flow, obtained from pressure and shear forces over the surface. A valid lift coefficient accounts for the chosen reference area, geometry, angle of attack and flow conditions. The optional weight comparison assumes vertical lift and omits other vertical forces; lift exceeding weight does not by itself establish a climb.
Example Problem
How to calculate a lift force?
In this example, we will explore the lift force exerted on an airplane wing. While the lift is very dependent on body shape, inclination, air viscosity, and compressibility, these are all factors taken into consideration with the coefficient of lift (which is usually calculated experimentally).
First, the coefficient of lift is determined to be 1.75.
Next, the density of the air must be determined. For this example, we will say the air is at standard pressure and density, so, the density is 1.225 kg/m^3.
Next, the area of the wing is calculated. In this problem, the wing area is found to be 5 m^2.
Next, use a true airspeed of 80 m/s for this numerical example; this is an assumed input, not a general average take-off speed.
Finally, calculate the lift force using the formula above.
Fl = Cl *A*(d*V^2)/2
= 1.75*5*((1.225*80^2)/2)
= 34,300 N
