Definition
The imaginary straight line along which the propeller or engine produces its forward pulling or pushing force. It runs through the propeller hub, parallel to the direction the thrust acts, and its position relative to the aircraft's center of gravity affects pitch behavior when power changes.
Plain English
It is the direction the engine is pulling the aircraft, drawn as a straight line through the propeller. Where this line sits compared to the aircraft's balance point decides whether adding power makes the nose want to rise or drop.
Context Anchor
Seen in pitch stability discussions when comparing the engine’s thrust path with the airplane’s balance point.
Derivation
Thrust' comes from Old Norse 'thrysta', meaning to push or press. Combined with 'line', it simply names the straight path along which the engine's push acts. Knowing this helps because the term is exactly what it says — a line showing the direction of the push.
Why Pilots Care
The thrust line's vertical position relative to the center of gravity produces nose-up or nose-down moments that influence trim and stability.
Grounding Statement
Picture adding power: the airplane does not just speed up; depending on where that push acts, the nose may also try to move.
Intuition Check
Do not think of line of thrust as a visible line on the airplane. It is an imaginary reference line showing where the engine’s force acts.
Example Sentence 1
Because the line of thrust passes above the center of gravity in this aircraft, applying full power during a go-around produces a noticeable nose-down tendency.
Example Sentence 2
Designers align the line of thrust near the center of gravity to reduce unwanted pitch changes when power is added or reduced.