Aerodynamic forces on aircraft

One of the major goals of aerodynamics is to predict the aerodynamic forces on aircraft.

The four basic forces that act on a powered aircraft are lift, weight, thrust, and drag.

Weight is the force due to gravity and thrust is the force generated by the engine. Lift and drag are aerodynamic forces. Lift is defined as the aerodynamic force acting perpendicular to the relative airflow and drag is defined as the aerodynamic force acting parallel to the relative airflow. Lift is positive upwards and drag is positive rearwards.