4 Forces Acting on an Airplane: Lift, Gravity, Thrust, Drag

Aeronautical Terms Defined
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There are four main forces that act on an airplane in flight: lift, weight, thrust, and drag. Understanding these forces and how they interact is essential to the safe and efficient operation of an aircraft.


Lift is the force that opposes gravity and holds the airplane in the air. It is generated by the wings and is proportional to the speed of the aircraft and the angle of attack. The angle of attack is the angle between the wing and the oncoming air, and it determines the amount of lift generated by the wings.

Gravity (Weight)

Weight, also known as gravity, is the force that pulls an aircraft towards the center of the earth. It is equal to the mass of the aircraft multiplied by the acceleration due to gravity. The weight of the aircraft is constant and acts vertically downwards.


Thrust is the force that propels the aircraft forward. It is generated by the engine and opposes the drag force. The amount of thrust required to maintain a steady speed depends on the airspeed, altitude, and aircraft weight.

In a glider, thrust is generated by the movement of the glider through the air. It is not provided by an engine as in a powered aircraft, but instead by the glider gaining altitude through thermal currents or by being towed into the air.


Drag is the force that opposes the thrust and slows the aircraft down. It is caused by the friction and pressure differences in the air as it moves over the surface of the aircraft. The amount of drag depends on the airspeed, altitude, and aircraft design.

In flight, the four forces acting on an aircraft must be balanced in order to maintain stability and control. Pilots must continuously adjust the thrust and angle of attack to maintain a stable flight. Understanding the interplay of these four forces is essential for safe and efficient flight operations.



Posted February 4, 2023