Aircraft Motion
Physics of Aircraft
Weight and Thrust
Secondary Controls
Straight and Level
Aircraft Design Features
The Stall
Practice Exam

The Lift Formula

The different factors that change lift are summed up by the lift formula:

Lift = CL ½ ρ V2 S

In this formula:

CL is the coefficient of lift
ρ is the air density
V is the true airspeed (velocity)
S is the surface area of the wing

The wing surface area is chosen by the aircraft designers and the air density depends on the atmosphere so we cannot change these two values. We have already learnt how lift varies with airspeed – but what is the coefficient of lift?

Coefficient of Lift

The Coefficient of Lift is a number that tells us how much lift a wing can create. It is based on many factors and is determined by the engineers who design the aircraft.

We’re not concerned with the actual value of CL. We do however, need to understand how the CL varies with angle of attack:

As angle of attack is increased, the lift coefficient increases up to the point of the Maximum Coefficient of Lift (CLMAX). Beyond this point, any further increase in angle of attack leads to a decrease in the coefficient of lift (and thus a decrease in the total lift created by the wing).
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