12.60 Straight and Level Flight

12.60.2 Define the four main forces acting in flight.

The four main forces acting in flight are lift, weight, thrust, and drag. Lift is the force that opposes gravity and keeps the aircraft in the air. It is generated by the wings of the aircraft as they move through the air. Weight is the force of gravity acting on the aircraft. It is the force that pulls the aircraft towards the ground. Thrust is the force that propels the aircraft forward. It is generated by the engines of the aircraft. Drag is the force that opposes the motion of the aircraft through the air. It is caused by the friction between the aircraft and the air, as well as other factors such as turbulence and the shape of the aircraft. In order for an aircraft to fly, the forces of lift and weight must be balanced, and the forces of thrust and drag must be balanced. If these forces are not balanced, the aircraft will either climb or descend, or speed up or slow down. In summary, the four main forces acting in flight are lift, weight, thrust, and drag. These forces must be balanced in order for the aircraft to fly.

12.60.4 For level flight describe how the four main forces change as IAS is varied.