Nashville CFI

Four Fundamental Forces of Flight

4 fundamental forces

The four forces are balanced here in forward flight.

4 fundamental forces balanced

The helicopter is slowing down here because the forces are not balanced (drag is greater than thrust).

4 fundamental forces slowing


Bernoulli's Principle says we have an area of low static pressure above the airfoil. Newton's Third Law tells us we have a force acting opposite (upward) to the air being forced off the bottom of the airflow. These two gentlemen, plus magic, give us lift.

airfoil lift

Lift Equation

L = Cl x P/2 x S x V2


Induced drag is greatest at slow airspeeds. Induced drag is a by-product of the production of lift.

induced drag

Total drag is defined as: Total drag = induced + parasite = profile drag.

We can minimize total drag at some airspeed, usually in the range of Vy. The point at which drag is at a minimum is called LDmax.


Form drag of various airfoils.