It has been observed that most aircraft accidents occur during the take-off or landing phase of the flight. Lift is a major part of takeoff. Before getting technical and diving right into the, let’s understand what lift is in simple terms. This will make it easier to grasp the concepts involved in the equation itself.
So, what is lift? Basically, lift is a force that causes an aircraft to fly. It either equals or exceeds gravitational force to create a tendency to rise into the air. The force that pushes up under the wings of an aeroplane, given the right circumstances and conditions, is lift.
What is the Lift Equation?
The lift equation is a mathematical representation which can be used to properly measure an aircraft’s lifting capabilities. The lift generated by an aircraft depends on a number of factors that are listed below:
- Air density
- Velocity between the air and the object
- Compressibility and viscosity of air
- The surface area of the wing of the aircraft
- Shape of the body under consideration
- And finally, the angle of attack (e. the body’s inclination relative to the flow)
Who uses the lift equation?
The lift equation is required to calculate the lift Coefficient used by aerodynamicists, to design all of the complex dependencies of inclination, some flow conditions, and shape of lift.
Definition of the lift Equation
In reality, the calculation of precise lift values on an aircraft’s wing is very complex, involving factors and parameters such as body shape and air viscosity. Therefore, a simplified model is often used, with the equation:
L=1/2 ρv2 Sref CL
- L denotes lift force.
- V defines the velocity of aircraft expressed in m/s.
- ρ is air density, affected by altitude.
- Sref is the reference area or the wing area of an aircraft measured in square metres.
- CL is the coefficient of lift, depending on the angle of attack and the type of aerofoil.
In the lift equation, v is also known as the true airspeed. This is defined as the real, measured speed that the aircraft attains in flight.
Similarly, ρ is air density, so the value of this variable depends on the height at which you want to find the lift and if it changes, altitude is influenced too.
We know that the lift formula is dependent on its component properties. So, if you change any one of these variables then the amount of lift will also change. Consider the following example, if you just change the velocity, keeping everything else constant in the lift equation, the amount of lift force will change, and the altitude of the aircraft will start to vary. Therefore, precise take off speeds are very important when flying and aircraft.
The inner workings of the lift equation – everything you need to know
Now, let’s break down the lift equation and examine it’s constituent parts.
Dynamic energy, (1/2 V2)
Air density multiplied by true airspeed will result in dynamic energy. Dynamic energy is caused by the aircraft movement which disturbs the surrounding air stream.
Coefficient lift (CL)
The lift coefficient CL is influenced by air viscosity and compressibility. It is a dimensionless value which is dependent on the air craft being examined.
Any given aircraft wing always lifts at the same CL max (with a specific angle of attack) for that configuration.
Angle of Attack, (AOA)
Angle of Attack also referred to as AOA, is basically the angle at which wind moves against an aerofoil. It is formed by a chord of the aerofoil and the direction of the vector defining the motion. In non-technical language, angle of attack is the difference between the direction a wing is pointing and where it is actually heading.
Wing area, (Sref)
Wing Area, denoted by Sref, is the surface area. Changing it will result in a change in the amount of lift experienced by the air craft.
To sum it all up, the lift equation has made things very easy for aerodynamicists and engineers. If you use the modern lift equation, and consider the lift coefficient given above, you can easily calculate the amount of lift produced at a given velocity for a given wing area.
In a different scenario, where wing area is not mentioned, and where we have been given velocity, we can also determine how large the wings need to be to be able to lift a certain weight, using the lift equation.