Definition
A cyclic-mounted switch in a helicopter that temporarily releases the artificial spring-loaded centering force on the cyclic control, allowing the pilot to reposition the cyclic without fighting the trim system, and then re-engages the springs to hold the new position as the new neutral reference point.
Plain English
A button on the cyclic stick that lets the pilot move the stick freely for a moment. When released, the stick stays put in the new spot and the springs hold it there.
Context Anchor
Seen in helicopter instrument flying when using stabilization or an automatic flight control system to reduce control pressure and help hold a steady attitude.
Derivation
Force' refers to the spring pressure pushing the cyclic toward a set position. 'Trim' comes from the older sailing and aviation idea of adjusting controls so the craft holds a steady attitude without constant pilot effort. 'Force trim' literally means trimming by means of a holding force.
Why Pilots Care
Reduces pilot workload by allowing stable hands-off flight attitudes once trimmed, which is especially useful in instrument conditions.
Analogy
It is like resetting the resting position of a spring-loaded handle. You move the handle to where you want it, then let the system hold that new spot.
Intuition Check
Do not read force trim as adding engine power or forcing the helicopter to fly a path. It mainly changes the control pressure and the position the controls tend to hold.
Example Sentence 1
Before starting the approach, the pilot pressed the force trim switch, repositioned the cyclic for level flight, and released it so the springs would hold the new attitude.
Example Sentence 2
During an ILS approach in turbulence, the pilot used the force trim switch to relieve control pressure and maintain a stable descent.