Definition
A secondary flight control that adjusts a small aerodynamic surface (a trim tab) on the elevator, rudder, or aileron so the airplane will hold a desired pitch, yaw, or bank attitude without the pilot having to maintain continuous pressure on the primary flight controls.
Plain English
A small wheel, crank, or switch in the cockpit that takes the constant push or pull off the control yoke or pedals, letting the airplane fly steadily on its own at the attitude you've set.
Context Anchor
Seen and used in the cockpit during attitude flying, especially after changing speed, power, climb, descent, or level-flight settings.
Derivation
From the nautical word 'trim,' meaning to balance or adjust a vessel so it sits properly in the water. The same idea carries into aviation: adjusting the airplane so it sits properly in the air without the pilot having to hold it there.
Why Pilots Care
Correct trim reduces fatigue on long flights, prevents unintended pitch changes, and allows the pilot to make small attitude adjustments more precisely.
Intuition Check
Do not read “trim” as making something neat or decorative. In this context, trim means adjusting the airplane so less steady hand force is needed on the controls.
Example Sentence 1
After leveling off at cruise altitude and setting cruise power, the pilot adjusted the trim control until the yoke could be released without the nose pitching up or down.
Example Sentence 2
During a power change the student adjusted the trim control to remove the new pitch tendency before continuing the climb.