Four Fundamental Forces of Flight
- Lift
- Thrust
- Weight
- Drag
![4 fundamental forces](/images/helicopter-fundamentals-aero4fund.jpg)
The four forces are balanced here in forward flight.
![4 fundamental forces balanced](/images/helicopter-fundamentals-aero4fundbalanced.jpg)
The helicopter is slowing down here because the forces are not balanced (drag is greater than thrust).
![4 fundamental forces slowing](/images/helicopter-fundamentals-aero4fundslowing.jpg)
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.
![airfoil lift](/images/helicopter-fundamentals-aeroairfoillift.jpg)
Lift Equation
L = Cl x P/2 x S x V2
Drag
Induced drag is greatest at slow airspeeds. Induced drag is a by-product of the production of lift.
![induced drag](/images/helicopter-fundamentals-aerodraginduced.jpg)
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.
![ldmax](/images/helicopter-fundamentals-aerodragldmax.jpg)
Form drag of various airfoils.
![drag](/images/helicopter-fundamentals-aerodrag.jpg)