Pilot’s Handbook of Aeronautical Knowledge FAA-H-8083-25A – Single PDF

Chapter 4 Aerodynamics of Flight

Thrust—the forward force produced by the powerplant/propeller or rotor. It opposes or overcomes the force of drag. As a general rule, it acts parallel to the longitudinal axis. However, this is not always the case, as explained later.

Drag—a rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects. Drag opposes thrust, and acts rearward parallel to the relative wind.

Weight—the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Weight pulls the aircraft downward because of the force of gravity. It opposes lift, and acts vertically downward through the aircraft’s center of gravity (CG).

Lift—opposes the downward force of weight, is produced by the dynamic effect of the air acting on the airfoil, and acts perpendicular to the flightpath through the center of lift.

Therefore, in steady flight: • The sum of all upward forces (not just lift) equals the sum of all downward forces (not just weight). • The sum of all forward forces (not just thrust) equals the sum of all backward forces (not just drag).

angle of attack (AOA)—the acute angle between the chord line of the airfoil and the direction of the relative wind

When the airspeed is low, the AOA must be relatively high if the balance between lift and weight is to be maintained.