#### Four Fundamental Forces of Flight

- Lift
- Thrust
- Weight
- Drag

The four forces are balanced here in forward flight.

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

**Lift**

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.

**Lift Equation**

L = C

_{l}x P/2 x S x V

^{2}

**Drag**

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

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

We can minimize total drag at some airspeed, usually in the range of V

_{y}. The point at which drag is at a minimum is called LD

_{max}.

Form drag of various airfoils.