Microlight » Aircraft Tech Knowledge » Forces acting on the aircraft
There are four forces which act upon an aircraft in flight.
Lift, weight, thrust and drag.
Lift is produced when air flows over an aerofoil, be it a wing or rotor blade.
Lift acts at 90 degrees to the Relative Airflow.
The price we pay for the lifting force on a wing or rotor blade is drag.
Drag is the aerodynamic force parallel to the relative airflow.
The weight of the aircraft may be represented by a single vector acting towards the centre of the earth, through the aircraft's centre of gravity (CoG).
In an Aeroplane or Gyrocopter thrust is provided by the propeller or jet airflow and is the force to overcome drag.
In a helicopter, the thrust is provided by the rotor blades.
Straight and Level
For an aircraft to fly straight and level, it must maintain a constant height, speed and direction.
Thrust must equal drag; and
lift must equal weight.
A state of equilibrium or zero acceleration .