Plain English Meaning

Four pushes and pulls act on every airplane in the air: one lifts it up, one pulls it down, one pushes it forward, and one holds it back. When they're balanced, the airplane keeps doing whatever it's already doing — flying level, climbing steadily, or descending steadily.

Full Definition

The four aerodynamic forces that act on an airplane in flight: lift, weight, thrust, and drag. Lift acts upward, opposing weight, which acts downward toward the center of the earth. Thrust acts forward along the flight path, and drag acts rearward, opposing thrust. In steady, unaccelerated flight these forces are in equilibrium — lift equals weight and thrust equals drag.

Context Anchor

Seen in basic flight theory, aircraft control, , , , and discussions about why the airplane responds the way it does.