Definition
The aerodynamic loads acting on the flight controls that the pilot must counter through stick or yoke pressure when the airplane is not trimmed for the current flight condition. When the trim system is set for one configuration or airspeed and the airplane then transitions to another, the elevator (or other control surface) is held out of its trimmed position by airflow, producing a steady force the pilot feels in the controls.
Plain English
The push or pull you feel on the controls when the airplane is set up to fly hands-off at one speed or attitude, but you're now flying at a different one. The airplane is trying to return to its trimmed condition, and you're holding the controls against that pull.
Context Anchor
Seen in elevator trim stall training, especially during go-arounds or other moments when a large nose-up trim setting can make the airplane pitch up quickly.
Derivation
Trim comes from Old English trymman, meaning to set in order or arrange properly. In aviation, trimming the airplane means arranging the controls so it flies steady on its own. Trim forces, then, are the forces that show up when that arrangement no longer matches the flight condition.
Why Pilots Care
Understanding trim forces helps pilots anticipate control pressures during maneuvers like go-arounds or stalls, preventing loss of control or excessive workload.
Intuition Check
Trim forces are not the same thing as engine power or lift. They are the push or pull on the controls created by the trim setting.
Example Sentence 1
When the pilot advanced to full power for the go-around, the strong nose-up trim forces required firm forward pressure on the yoke until the airplane could be retrimmed.
Example Sentence 2
In the elevator trim stall exercise, releasing the controls with excessive nose-up trim caused a rapid pitch-up due to the unbalanced trim forces.