Forces Acting on the Aircraft

Four Forces

There are four main forces acting on an aircraft in flight:

• Lift
• Weight
• Thrust
• Drag

Lift

Lift is produced when air flows over an aerofoil, such as a wing or rotor blade.

Lift acts at 90° to the Relative Airflow.

Drag

Drag is the aerodynamic force which opposes the aircraft's movement through the air.

Drag acts parallel to the Relative Airflow and opposite to the direction of flight.

Weight

Weight is the force of gravity acting on the aircraft.

It acts vertically towards the centre of the Earth through the aircraft's Centre of Gravity (CoG).

Thrust

In an aeroplane or gyrocopter, thrust is normally produced by the propeller or jet engine and provides the force required to overcome drag.

In a helicopter, the rotor provides the aerodynamic force required to support and move the aircraft.

Straight and Level

For an aircraft to remain in steady straight and level flight, it must maintain a constant:

• height
• airspeed
• direction

In straight and level flight:

Lift = Weight

and

Thrust = Drag

The aircraft is in a state of equilibrium, meaning there is no acceleration.

Turning

An aircraft travelling in a straight line will continue in that direction unless acted upon by a force.